const std = @import("std");
const builtin = @import("builtin");
const glfw = @import("glfw");
const xev = @import("xev");
const apprt = @import("../apprt.zig");
const configpkg = @import("../config.zig");
const font = @import("../font/main.zig");
const os = @import("../os/main.zig");
const terminal = @import("../terminal/main.zig");
const renderer = @import("../renderer.zig");
const math = @import("../math.zig");
const Surface = @import("../Surface.zig");
const link = @import("link.zig");
const fgMode = @import("cell.zig").fgMode;
const isCovering = @import("cell.zig").isCovering;
const shadertoy = @import("shadertoy.zig");
const assert = std.debug.assert;
const Allocator = std.mem.Allocator;
const ArenaAllocator = std.heap.ArenaAllocator;
const Terminal = terminal.Terminal;
const Health = renderer.Health;

const macos = switch (builtin.os.tag) {
    .macos => @import("macos"),
    else => void,
};

const DisplayLink = switch (builtin.os.tag) {
    .macos => *macos.video.DisplayLink,
    else => void,
};

const log = std.log.scoped(.generic_renderer);

/// Create a renderer type with the provided graphics API wrapper.
///
/// The graphics API wrapper must provide the interface outlined below.
/// Specific details for the interfaces are documented on the existing
/// implementations (`Metal` and `OpenGL`).
///
/// Hierarchy of graphics abstractions:
///
/// [ GraphicsAPI ] - Responsible for configuring the runtime surface
///    |     |        and providing render `Target`s that draw to it,
///    |     |        as well as `Frame`s and `Pipeline`s.
///    |     V
///    | [ Target ] - Represents an abstract target for rendering, which
///    |              could be a surface directly but is also used as an
///    |              abstraction for off-screen frame buffers.
///    V
/// [ Frame ] - Represents the context for drawing a given frame,
///    |        provides `RenderPass`es for issuing draw commands
///    |        to, and reports the frame health when complete.
///    V
/// [ RenderPass ] - Represents a render pass in a frame, consisting of
///   :              one or more `Step`s applied to the same target(s),
/// [ Step ] - - - - each describing the input buffers and textures and
///   :              the vertex/fragment functions and geometry to use.
///   :_ _ _ _ _ _ _ _ _ _/
///   v
/// [ Pipeline ] - Describes a vertex and fragment function to be used
///                for a `Step`; the `GraphicsAPI` is responsible for
///                these and they should be constructed and cached
///                ahead of time.
///
/// [ Buffer ] - An abstraction over a GPU buffer.
///
/// [ Texture ] - An abstraction over a GPU texture.
///
pub fn Renderer(comptime GraphicsAPI: type) type {
    return struct {
        const Self = @This();

        const Target = GraphicsAPI.Target;
        const Buffer = GraphicsAPI.Buffer;
        const Texture = GraphicsAPI.Texture;
        const RenderPass = GraphicsAPI.RenderPass;
        const shaderpkg = GraphicsAPI.shaders;

        const cellpkg = GraphicsAPI.cellpkg;
        const imagepkg = GraphicsAPI.imagepkg;
        const Image = imagepkg.Image;
        const ImageMap = imagepkg.ImageMap;

        const Shaders = shaderpkg.Shaders;

        const ImagePlacementList = std.ArrayListUnmanaged(imagepkg.Placement);

        /// Allocator that can be used
        alloc: std.mem.Allocator,

        /// This mutex must be held whenever any state used in `drawFrame` is
        /// being modified, and also when it's being accessed in `drawFrame`.
        draw_mutex: std.Thread.Mutex = .{},

        /// The configuration we need derived from the main config.
        config: DerivedConfig,

        /// The mailbox for communicating with the window.
        surface_mailbox: apprt.surface.Mailbox,

        /// Current font metrics defining our grid.
        grid_metrics: font.Metrics,

        /// The size of everything.
        size: renderer.Size,

        /// True if the window is focused
        focused: bool,

        /// The foreground color set by an OSC 10 sequence. If unset then
        /// default_foreground_color is used.
        foreground_color: ?terminal.color.RGB,

        /// Foreground color set in the user's config file.
        default_foreground_color: terminal.color.RGB,

        /// The background color set by an OSC 11 sequence. If unset then
        /// default_background_color is used.
        background_color: ?terminal.color.RGB,

        /// Background color set in the user's config file.
        default_background_color: terminal.color.RGB,

        /// The cursor color set by an OSC 12 sequence. If unset then
        /// default_cursor_color is used.
        cursor_color: ?terminal.color.RGB,

        /// Default cursor color when no color is set explicitly by an OSC 12 command.
        /// This is cursor color as set in the user's config, if any. If no cursor color
        /// is set in the user's config, then the cursor color is determined by the
        /// current foreground color.
        default_cursor_color: ?terminal.color.RGB,

        /// When `cursor_color` is null, swap the foreground and background colors of
        /// the cell under the cursor for the cursor color. Otherwise, use the default
        /// foreground color as the cursor color.
        cursor_invert: bool,

        /// The current set of cells to render. This is rebuilt on every frame
        /// but we keep this around so that we don't reallocate. Each set of
        /// cells goes into a separate shader.
        cells: cellpkg.Contents,

        /// The last viewport that we based our rebuild off of. If this changes,
        /// then we do a full rebuild of the cells. The pointer values in this pin
        /// are NOT SAFE to read because they may be modified, freed, etc from the
        /// termio thread. We treat the pointers as integers for comparison only.
        cells_viewport: ?terminal.Pin = null,

        /// Set to true after rebuildCells is called. This can be used
        /// to determine if any possible changes have been made to the
        /// cells for the draw call.
        cells_rebuilt: bool = false,

        /// The current GPU uniform values.
        uniforms: shaderpkg.Uniforms,

        /// The font structures.
        font_grid: *font.SharedGrid,
        font_shaper: font.Shaper,
        font_shaper_cache: font.ShaperCache,

        /// The images that we may render.
        images: ImageMap = .{},
        image_placements: ImagePlacementList = .{},
        image_bg_end: u32 = 0,
        image_text_end: u32 = 0,
        image_virtual: bool = false,

        /// Graphics API state.
        api: GraphicsAPI,

        /// The CVDisplayLink used to drive the rendering loop in
        /// sync with the display. This is void on platforms that
        /// don't support a display link.
        display_link: ?DisplayLink = null,

        /// Health of the most recently completed frame.
        health: std.atomic.Value(Health) = .{ .raw = .healthy },

        /// Our swap chain (multiple buffering)
        swap_chain: SwapChain,

        /// This value is used to force-update swap chain targets in the
        /// event of a config change that requires it (such as blending mode).
        target_config_modified: usize = 0,

        /// If something happened that requires us to reinitialize our shaders,
        /// this is set to true so that we can do that whenever possible.
        reinitialize_shaders: bool = false,

        /// Whether or not we have custom shaders.
        has_custom_shaders: bool = false,

        /// Our shader pipelines.
        shaders: Shaders,

        /// Swap chain which maintains multiple copies of the state needed to
        /// render a frame, so that we can start building the next frame while
        /// the previous frame is still being processed on the GPU.
        const SwapChain = struct {
            // The count of buffers we use for double/triple buffering.
            // If this is one then we don't do any double+ buffering at all.
            // This is comptime because there isn't a good reason to change
            // this at runtime and there is a lot of complexity to support it.
            const buf_count = GraphicsAPI.swap_chain_count;

            /// `buf_count` structs that can hold the
            /// data needed by the GPU to draw a frame.
            frames: [buf_count]FrameState,
            /// Index of the most recently used frame state struct.
            frame_index: std.math.IntFittingRange(0, buf_count) = 0,
            /// Semaphore that we wait on to make sure we have an available
            /// frame state struct so we can start working on a new frame.
            frame_sema: std.Thread.Semaphore = .{ .permits = buf_count },

            /// Set to true when deinited, if you try to deinit a defunct
            /// swap chain it will just be ignored, to prevent double-free.
            ///
            /// This is required because of `displayUnrealized`, since it
            /// `deinits` the swapchain, which leads to a double-free if
            /// the renderer is deinited after that.
            defunct: bool = false,

            pub fn init(api: GraphicsAPI, custom_shaders: bool) !SwapChain {
                var result: SwapChain = .{ .frames = undefined };

                // Initialize all of our frame state.
                for (&result.frames) |*frame| {
                    frame.* = try FrameState.init(api, custom_shaders);
                }

                return result;
            }

            pub fn deinit(self: *SwapChain) void {
                if (self.defunct) return;
                self.defunct = true;

                // Wait for all of our inflight draws to complete
                // so that we can cleanly deinit our GPU state.
                for (0..buf_count) |_| self.frame_sema.wait();
                for (&self.frames) |*frame| frame.deinit();
            }

            /// Get the next frame state to draw to. This will wait on the
            /// semaphore to ensure that the frame is available. This must
            /// always be paired with a call to releaseFrame.
            pub fn nextFrame(self: *SwapChain) error{Defunct}!*FrameState {
                if (self.defunct) return error.Defunct;

                self.frame_sema.wait();
                errdefer self.frame_sema.post();
                self.frame_index = (self.frame_index + 1) % buf_count;
                return &self.frames[self.frame_index];
            }

            /// This should be called when the frame has completed drawing.
            pub fn releaseFrame(self: *SwapChain) void {
                self.frame_sema.post();
            }
        };

        /// State we need duplicated for every frame. Any state that could be
        /// in a data race between the GPU and CPU while a frame is being drawn
        /// should be in this struct.
        ///
        /// While a draw is in-process, we "lock" the state (via a semaphore)
        /// and prevent the CPU from updating the state until our graphics API
        /// reports that the frame is complete.
        ///
        /// This is used to implement double/triple buffering.
        const FrameState = struct {
            uniforms: UniformBuffer,
            cells: CellTextBuffer,
            cells_bg: CellBgBuffer,

            grayscale: Texture,
            grayscale_modified: usize = 0,
            color: Texture,
            color_modified: usize = 0,

            target: Target,
            /// See property of same name on Renderer for explanation.
            target_config_modified: usize = 0,

            /// Custom shader state, this is null if we have no custom shaders.
            custom_shader_state: ?CustomShaderState = null,

            /// A buffer containing the uniform data.
            const UniformBuffer = Buffer(shaderpkg.Uniforms);
            const CellBgBuffer = Buffer(shaderpkg.CellBg);
            const CellTextBuffer = Buffer(shaderpkg.CellText);

            pub fn init(api: GraphicsAPI, custom_shaders: bool) !FrameState {
                // Uniform buffer contains exactly 1 uniform struct. The
                // uniform data will be undefined so this must be set before
                // a frame is drawn.
                var uniforms = try UniformBuffer.init(api.uniformBufferOptions(), 1);
                errdefer uniforms.deinit();

                // Create GPU buffers for our cells.
                //
                // We start them off with a size of 1, which will of course be
                // too small, but they will be resized as needed. This is a bit
                // wasteful but since it's a one-time thing it's not really a
                // huge concern.
                var cells = try CellTextBuffer.init(api.fgBufferOptions(), 1);
                errdefer cells.deinit();
                var cells_bg = try CellBgBuffer.init(api.bgBufferOptions(), 1);
                errdefer cells_bg.deinit();

                // Initialize our textures for our font atlas.
                //
                // As with the buffers above, we start these off as small
                // as possible since they'll inevitably be resized anyway.
                const grayscale = try api.initAtlasTexture(&.{
                    .data = undefined,
                    .size = 1,
                    .format = .grayscale,
                });
                errdefer grayscale.deinit();
                const color = try api.initAtlasTexture(&.{
                    .data = undefined,
                    .size = 1,
                    .format = .rgba,
                });
                errdefer color.deinit();

                var custom_shader_state =
                    if (custom_shaders)
                        try CustomShaderState.init(api)
                    else
                        null;
                errdefer if (custom_shader_state) |*state| state.deinit();

                // Initialize the target. Just as with the other resources,
                // start it off as small as we can since it'll be resized.
                const target = try api.initTarget(1, 1);

                return .{
                    .uniforms = uniforms,
                    .cells = cells,
                    .cells_bg = cells_bg,
                    .grayscale = grayscale,
                    .color = color,
                    .target = target,
                    .custom_shader_state = custom_shader_state,
                };
            }

            pub fn deinit(self: *FrameState) void {
                self.uniforms.deinit();
                self.cells.deinit();
                self.cells_bg.deinit();
                self.grayscale.deinit();
                self.color.deinit();
                if (self.custom_shader_state) |*state| state.deinit();
            }

            pub fn resize(
                self: *FrameState,
                api: GraphicsAPI,
                width: usize,
                height: usize,
            ) !void {
                if (self.custom_shader_state) |*state| {
                    try state.resize(api, width, height);
                }
                const target = try api.initTarget(width, height);
                self.target.deinit();
                self.target = target;
            }
        };

        /// State relevant to our custom shaders if we have any.
        const CustomShaderState = struct {
            /// When we have a custom shader state, we maintain a front
            /// and back texture which we use as a swap chain to render
            /// between when multiple custom shaders are defined.
            front_texture: Texture,
            back_texture: Texture,

            uniforms: shaderpkg.PostUniforms,

            /// The first time a frame was drawn.
            /// This is used to update the time uniform.
            first_frame_time: std.time.Instant,

            /// The last time a frame was drawn.
            /// This is used to update the time uniform.
            last_frame_time: std.time.Instant,

            /// Swap the front and back textures.
            pub fn swap(self: *CustomShaderState) void {
                std.mem.swap(Texture, &self.front_texture, &self.back_texture);
            }

            pub fn init(api: GraphicsAPI) !CustomShaderState {
                // Initialize the front and back textures at 1x1 px, this
                // is slightly wasteful but it's only done once so whatever.
                const front_texture = try Texture.init(
                    api.textureOptions(),
                    1,
                    1,
                    null,
                );
                errdefer front_texture.deinit();
                const back_texture = try Texture.init(
                    api.textureOptions(),
                    1,
                    1,
                    null,
                );
                errdefer back_texture.deinit();
                return .{
                    .front_texture = front_texture,
                    .back_texture = back_texture,

                    .uniforms = .{
                        .resolution = .{ 0, 0, 1 },
                        .time = 1,
                        .time_delta = 1,
                        .frame_rate = 1,
                        .frame = 1,
                        .channel_time = @splat(@splat(0)),
                        .channel_resolution = @splat(@splat(0)),
                        .mouse = .{ 0, 0, 0, 0 },
                        .date = .{ 0, 0, 0, 0 },
                        .sample_rate = 1,
                    },

                    .first_frame_time = try std.time.Instant.now(),
                    .last_frame_time = try std.time.Instant.now(),
                };
            }

            pub fn deinit(self: *CustomShaderState) void {
                self.front_texture.deinit();
                self.back_texture.deinit();
            }

            pub fn resize(
                self: *CustomShaderState,
                api: GraphicsAPI,
                width: usize,
                height: usize,
            ) !void {
                const front_texture = try Texture.init(
                    api.textureOptions(),
                    @intCast(width),
                    @intCast(height),
                    null,
                );
                errdefer front_texture.deinit();
                const back_texture = try Texture.init(
                    api.textureOptions(),
                    @intCast(width),
                    @intCast(height),
                    null,
                );
                errdefer back_texture.deinit();

                self.front_texture.deinit();
                self.back_texture.deinit();

                self.front_texture = front_texture;
                self.back_texture = back_texture;

                self.uniforms.resolution = .{
                    @floatFromInt(width),
                    @floatFromInt(height),
                    1,
                };
                self.uniforms.channel_resolution[0] = .{
                    @floatFromInt(width),
                    @floatFromInt(height),
                    1,
                    0,
                };
            }
        };

        /// The configuration for this renderer that is derived from the main
        /// configuration. This must be exported so that we don't need to
        /// pass around Config pointers which makes memory management a pain.
        pub const DerivedConfig = struct {
            arena: ArenaAllocator,

            font_thicken: bool,
            font_thicken_strength: u8,
            font_features: std.ArrayListUnmanaged([:0]const u8),
            font_styles: font.CodepointResolver.StyleStatus,
            cursor_color: ?terminal.color.RGB,
            cursor_invert: bool,
            cursor_opacity: f64,
            cursor_text: ?terminal.color.RGB,
            background: terminal.color.RGB,
            background_opacity: f64,
            foreground: terminal.color.RGB,
            selection_background: ?terminal.color.RGB,
            selection_foreground: ?terminal.color.RGB,
            invert_selection_fg_bg: bool,
            bold_is_bright: bool,
            min_contrast: f32,
            padding_color: configpkg.WindowPaddingColor,
            custom_shaders: configpkg.RepeatablePath,
            links: link.Set,
            vsync: bool,
            colorspace: configpkg.Config.WindowColorspace,
            blending: configpkg.Config.AlphaBlending,

            pub fn init(
                alloc_gpa: Allocator,
                config: *const configpkg.Config,
            ) !DerivedConfig {
                var arena = ArenaAllocator.init(alloc_gpa);
                errdefer arena.deinit();
                const alloc = arena.allocator();

                // Copy our shaders
                const custom_shaders = try config.@"custom-shader".clone(alloc);

                // Copy our font features
                const font_features = try config.@"font-feature".clone(alloc);

                // Get our font styles
                var font_styles = font.CodepointResolver.StyleStatus.initFill(true);
                font_styles.set(.bold, config.@"font-style-bold" != .false);
                font_styles.set(.italic, config.@"font-style-italic" != .false);
                font_styles.set(.bold_italic, config.@"font-style-bold-italic" != .false);

                // Our link configs
                const links = try link.Set.fromConfig(
                    alloc,
                    config.link.links.items,
                );

                const cursor_invert = config.@"cursor-invert-fg-bg";

                return .{
                    .background_opacity = @max(0, @min(1, config.@"background-opacity")),
                    .font_thicken = config.@"font-thicken",
                    .font_thicken_strength = config.@"font-thicken-strength",
                    .font_features = font_features.list,
                    .font_styles = font_styles,

                    .cursor_color = if (!cursor_invert and config.@"cursor-color" != null)
                        config.@"cursor-color".?.toTerminalRGB()
                    else
                        null,

                    .cursor_invert = cursor_invert,

                    .cursor_text = if (config.@"cursor-text") |txt|
                        txt.toTerminalRGB()
                    else
                        null,

                    .cursor_opacity = @max(0, @min(1, config.@"cursor-opacity")),

                    .background = config.background.toTerminalRGB(),
                    .foreground = config.foreground.toTerminalRGB(),
                    .invert_selection_fg_bg = config.@"selection-invert-fg-bg",
                    .bold_is_bright = config.@"bold-is-bright",
                    .min_contrast = @floatCast(config.@"minimum-contrast"),
                    .padding_color = config.@"window-padding-color",

                    .selection_background = if (config.@"selection-background") |bg|
                        bg.toTerminalRGB()
                    else
                        null,

                    .selection_foreground = if (config.@"selection-foreground") |bg|
                        bg.toTerminalRGB()
                    else
                        null,

                    .custom_shaders = custom_shaders,
                    .links = links,
                    .vsync = config.@"window-vsync",
                    .colorspace = config.@"window-colorspace",
                    .blending = config.@"alpha-blending",
                    .arena = arena,
                };
            }

            pub fn deinit(self: *DerivedConfig) void {
                const alloc = self.arena.allocator();
                self.links.deinit(alloc);
                self.arena.deinit();
            }
        };

        /// Returns the hints that we want for this window.
        pub fn glfwWindowHints(config: *const configpkg.Config) glfw.Window.Hints {
            // If our graphics API provides hints, use them,
            // otherwise fall back to generic hints.
            if (@hasDecl(GraphicsAPI, "glfwWindowHints")) {
                return GraphicsAPI.glfwWindowHints(config);
            }

            return .{
                .client_api = .no_api,
                .transparent_framebuffer = config.@"background-opacity" < 1,
            };
        }

        pub fn init(alloc: Allocator, options: renderer.Options) !Self {
            // Initialize our graphics API wrapper, this will prepare the
            // surface provided by the apprt and set up any API-specific
            // GPU resources.
            var api = try GraphicsAPI.init(alloc, options);
            errdefer api.deinit();

            const has_custom_shaders = options.config.custom_shaders.value.items.len > 0;

            // Prepare our swap chain
            var swap_chain = try SwapChain.init(
                api,
                has_custom_shaders,
            );
            errdefer swap_chain.deinit();

            // Create the font shaper.
            var font_shaper = try font.Shaper.init(alloc, .{
                .features = options.config.font_features.items,
            });
            errdefer font_shaper.deinit();

            // Initialize all the data that requires a critical font section.
            const font_critical: struct {
                metrics: font.Metrics,
            } = font_critical: {
                const grid: *font.SharedGrid = options.font_grid;
                grid.lock.lockShared();
                defer grid.lock.unlockShared();
                break :font_critical .{
                    .metrics = grid.metrics,
                };
            };

            const display_link: ?DisplayLink = switch (builtin.os.tag) {
                .macos => if (options.config.vsync)
                    try macos.video.DisplayLink.createWithActiveCGDisplays()
                else
                    null,
                else => null,
            };
            errdefer if (display_link) |v| v.release();

            var result: Self = .{
                .alloc = alloc,
                .config = options.config,
                .surface_mailbox = options.surface_mailbox,
                .grid_metrics = font_critical.metrics,
                .size = options.size,
                .focused = true,
                .foreground_color = null,
                .default_foreground_color = options.config.foreground,
                .background_color = null,
                .default_background_color = options.config.background,
                .cursor_color = null,
                .default_cursor_color = options.config.cursor_color,
                .cursor_invert = options.config.cursor_invert,

                // Render state
                .cells = .{},
                .uniforms = .{
                    .projection_matrix = undefined,
                    .cell_size = undefined,
                    .grid_size = undefined,
                    .grid_padding = undefined,
                    .padding_extend = .{},
                    .min_contrast = options.config.min_contrast,
                    .cursor_pos = .{ std.math.maxInt(u16), std.math.maxInt(u16) },
                    .cursor_color = undefined,
                    .bg_color = .{
                        options.config.background.r,
                        options.config.background.g,
                        options.config.background.b,
                        @intFromFloat(@round(options.config.background_opacity * 255.0)),
                    },
                    .bools = .{
                        .cursor_wide = false,
                        .use_display_p3 = options.config.colorspace == .@"display-p3",
                        .use_linear_blending = options.config.blending.isLinear(),
                        .use_linear_correction = options.config.blending == .@"linear-corrected",
                    },
                },

                // Fonts
                .font_grid = options.font_grid,
                .font_shaper = font_shaper,
                .font_shaper_cache = font.ShaperCache.init(),

                // Shaders (initialized below)
                .shaders = undefined,

                // Graphics API stuff
                .api = api,
                .swap_chain = swap_chain,
                .display_link = display_link,
            };

            try result.initShaders();

            // Ensure our undefined values above are correctly initialized.
            result.updateFontGridUniforms();
            result.updateScreenSizeUniforms();

            return result;
        }

        pub fn deinit(self: *Self) void {
            self.swap_chain.deinit();

            if (DisplayLink != void) {
                if (self.display_link) |display_link| {
                    display_link.stop() catch {};
                    display_link.release();
                }
            }

            self.cells.deinit(self.alloc);

            self.font_shaper.deinit();
            self.font_shaper_cache.deinit(self.alloc);

            self.config.deinit();

            {
                var it = self.images.iterator();
                while (it.next()) |kv| kv.value_ptr.image.deinit(self.alloc);
                self.images.deinit(self.alloc);
            }
            self.image_placements.deinit(self.alloc);

            self.deinitShaders();

            self.api.deinit();

            self.* = undefined;
        }

        fn deinitShaders(self: *Self) void {
            self.shaders.deinit(self.alloc);
        }

        fn initShaders(self: *Self) !void {
            var arena = ArenaAllocator.init(self.alloc);
            defer arena.deinit();
            const arena_alloc = arena.allocator();

            // Load our custom shaders
            const custom_shaders: []const [:0]const u8 = shadertoy.loadFromFiles(
                arena_alloc,
                self.config.custom_shaders,
                GraphicsAPI.custom_shader_target,
            ) catch |err| err: {
                log.warn("error loading custom shaders err={}", .{err});
                break :err &.{};
            };

            const has_custom_shaders = custom_shaders.len > 0;

            var shaders = try self.api.initShaders(
                self.alloc,
                custom_shaders,
            );
            errdefer shaders.deinit(self.alloc);

            self.shaders = shaders;
            self.has_custom_shaders = has_custom_shaders;
        }

        /// This is called early right after surface creation.
        pub fn surfaceInit(surface: *apprt.Surface) !void {
            // If our API has to do things here, let it.
            if (@hasDecl(GraphicsAPI, "surfaceInit")) {
                try GraphicsAPI.surfaceInit(surface);
            }
        }

        /// This is called just prior to spinning up the renderer thread for
        /// final main thread setup requirements.
        pub fn finalizeSurfaceInit(self: *Self, surface: *apprt.Surface) !void {
            // If our API has to do things to finalize surface init, let it.
            if (@hasDecl(GraphicsAPI, "finalizeSurfaceInit")) {
                try self.api.finalizeSurfaceInit(surface);
            }
        }

        /// Callback called by renderer.Thread when it begins.
        pub fn threadEnter(self: *const Self, surface: *apprt.Surface) !void {
            // If our API has to do things on thread enter, let it.
            if (@hasDecl(GraphicsAPI, "threadEnter")) {
                try self.api.threadEnter(surface);
            }
        }

        /// Callback called by renderer.Thread when it exits.
        pub fn threadExit(self: *const Self) void {
            // If our API has to do things on thread exit, let it.
            if (@hasDecl(GraphicsAPI, "threadExit")) {
                self.api.threadExit();
            }
        }

        /// Called by renderer.Thread when it starts the main loop.
        pub fn loopEnter(self: *Self, thr: *renderer.Thread) !void {
            // If our API has to do things on loop enter, let it.
            if (@hasDecl(GraphicsAPI, "loopEnter")) {
                self.api.loopEnter();
            }

            // If we don't support a display link we have no work to do.
            if (comptime DisplayLink == void) return;

            // This is when we know our "self" pointer is stable so we can
            // setup the display link. To setup the display link we set our
            // callback and we can start it immediately.
            const display_link = self.display_link orelse return;
            try display_link.setOutputCallback(
                xev.Async,
                &displayLinkCallback,
                &thr.draw_now,
            );
            display_link.start() catch {};
        }

        /// Called by renderer.Thread when it exits the main loop.
        pub fn loopExit(self: *Self) void {
            // If our API has to do things on loop exit, let it.
            if (@hasDecl(GraphicsAPI, "loopExit")) {
                self.api.loopExit();
            }

            // If we don't support a display link we have no work to do.
            if (comptime DisplayLink == void) return;

            // Stop our display link. If this fails its okay it just means
            // that we either never started it or the view its attached to
            // is gone which is fine.
            const display_link = self.display_link orelse return;
            display_link.stop() catch {};
        }

        /// This is called by the GTK apprt after the surface is
        /// reinitialized due to any of the events mentioned in
        /// the doc comment for `displayUnrealized`.
        pub fn displayRealized(self: *Self) !void {
            // If our API has to do things on realize, let it.
            if (@hasDecl(GraphicsAPI, "displayRealized")) {
                self.api.displayRealized();
            }

            // Lock the draw mutex so that we can
            // safely reinitialize our GPU resources.
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            // We assume that the swap chain was deinited in
            // `displayUnrealized`, in which case it should be
            // marked defunct. If not, we have a problem.
            assert(self.swap_chain.defunct);

            // We reinitialize our shaders and our swap chain.
            try self.initShaders();
            self.swap_chain = try SwapChain.init(
                self.api,
                self.has_custom_shaders,
            );
            self.reinitialize_shaders = false;
            self.target_config_modified = 1;
        }

        /// This is called by the GTK apprt when the surface is being destroyed.
        /// This can happen because the surface is being closed but also when
        /// moving the window between displays or splitting.
        pub fn displayUnrealized(self: *Self) void {
            // If our API has to do things on unrealize, let it.
            if (@hasDecl(GraphicsAPI, "displayUnrealized")) {
                self.api.displayUnrealized();
            }

            // Lock the draw mutex so that we can
            // safely deinitialize our GPU resources.
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            // We deinit our swap chain and shaders.
            //
            // This will mark them as defunct so that they
            // can't be double-freed or used in draw calls.
            self.swap_chain.deinit();
            self.shaders.deinit(self.alloc);
        }

        fn displayLinkCallback(
            _: *macos.video.DisplayLink,
            ud: ?*xev.Async,
        ) void {
            const draw_now = ud orelse return;
            draw_now.notify() catch |err| {
                log.err("error notifying draw_now err={}", .{err});
            };
        }

        /// Mark the full screen as dirty so that we redraw everything.
        pub fn markDirty(self: *Self) void {
            self.cells_viewport = null;
        }

        /// Called when we get an updated display ID for our display link.
        pub fn setMacOSDisplayID(self: *Self, id: u32) !void {
            if (comptime DisplayLink == void) return;
            const display_link = self.display_link orelse return;
            log.info("updating display link display id={}", .{id});
            display_link.setCurrentCGDisplay(id) catch |err| {
                log.warn("error setting display link display id err={}", .{err});
            };
        }

        /// True if our renderer has animations so that a higher frequency
        /// timer is used.
        pub fn hasAnimations(self: *const Self) bool {
            return self.has_custom_shaders;
        }

        /// True if our renderer is using vsync. If true, the renderer or apprt
        /// is responsible for triggering draw_now calls to the render thread.
        /// That is the only way to trigger a drawFrame.
        pub fn hasVsync(self: *const Self) bool {
            if (comptime DisplayLink == void) return false;
            const display_link = self.display_link orelse return false;
            return display_link.isRunning();
        }

        /// Callback when the focus changes for the terminal this is rendering.
        ///
        /// Must be called on the render thread.
        pub fn setFocus(self: *Self, focus: bool) !void {
            self.focused = focus;

            // If we're not focused, then we want to stop the display link
            // because it is a waste of resources and we can move to pure
            // change-driven updates.
            if (comptime DisplayLink != void) link: {
                const display_link = self.display_link orelse break :link;
                if (focus) {
                    display_link.start() catch {};
                } else {
                    display_link.stop() catch {};
                }
            }
        }

        /// Callback when the window is visible or occluded.
        ///
        /// Must be called on the render thread.
        pub fn setVisible(self: *Self, visible: bool) void {
            // If we're not visible, then we want to stop the display link
            // because it is a waste of resources and we can move to pure
            // change-driven updates.
            if (comptime DisplayLink != void) link: {
                const display_link = self.display_link orelse break :link;
                if (visible and self.focused) {
                    display_link.start() catch {};
                } else {
                    display_link.stop() catch {};
                }
            }
        }

        /// Set the new font grid.
        ///
        /// Must be called on the render thread.
        pub fn setFontGrid(self: *Self, grid: *font.SharedGrid) void {
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            // Update our grid
            self.font_grid = grid;

            // Update all our textures so that they sync on the next frame.
            // We can modify this without a lock because the GPU does not
            // touch this data.
            for (&self.swap_chain.frames) |*frame| {
                frame.grayscale_modified = 0;
                frame.color_modified = 0;
            }

            // Get our metrics from the grid. This doesn't require a lock because
            // the metrics are never recalculated.
            const metrics = grid.metrics;
            self.grid_metrics = metrics;

            // Reset our shaper cache. If our font changed (not just the size) then
            // the data in the shaper cache may be invalid and cannot be used, so we
            // always clear the cache just in case.
            const font_shaper_cache = font.ShaperCache.init();
            self.font_shaper_cache.deinit(self.alloc);
            self.font_shaper_cache = font_shaper_cache;

            // Update cell size.
            self.size.cell = .{
                .width = metrics.cell_width,
                .height = metrics.cell_height,
            };

            // Update relevant uniforms
            self.updateFontGridUniforms();
        }

        /// Update uniforms that are based on the font grid.
        ///
        /// Caller must hold the draw mutex.
        fn updateFontGridUniforms(self: *Self) void {
            self.uniforms.cell_size = .{
                @floatFromInt(self.grid_metrics.cell_width),
                @floatFromInt(self.grid_metrics.cell_height),
            };
        }

        /// Update the frame data.
        pub fn updateFrame(
            self: *Self,
            state: *renderer.State,
            cursor_blink_visible: bool,
        ) !void {
            // Data we extract out of the critical area.
            const Critical = struct {
                bg: terminal.color.RGB,
                screen: terminal.Screen,
                screen_type: terminal.ScreenType,
                mouse: renderer.State.Mouse,
                preedit: ?renderer.State.Preedit,
                cursor_style: ?renderer.CursorStyle,
                color_palette: terminal.color.Palette,

                /// If true, rebuild the full screen.
                full_rebuild: bool,
            };

            // Update all our data as tightly as possible within the mutex.
            var critical: Critical = critical: {
                // const start = try std.time.Instant.now();
                // const start_micro = std.time.microTimestamp();
                // defer {
                //     const end = std.time.Instant.now() catch unreachable;
                //     // "[updateFrame critical time] <START us>\t<TIME_TAKEN us>"
                //     std.log.err("[updateFrame critical time] {}\t{}", .{start_micro, end.since(start) / std.time.ns_per_us});
                // }

                state.mutex.lock();
                defer state.mutex.unlock();

                // If we're in a synchronized output state, we pause all rendering.
                if (state.terminal.modes.get(.synchronized_output)) {
                    log.debug("synchronized output started, skipping render", .{});
                    return;
                }

                // Swap bg/fg if the terminal is reversed
                const bg = self.background_color orelse self.default_background_color;
                const fg = self.foreground_color orelse self.default_foreground_color;
                defer {
                    if (self.background_color) |*c| {
                        c.* = bg;
                    } else {
                        self.default_background_color = bg;
                    }

                    if (self.foreground_color) |*c| {
                        c.* = fg;
                    } else {
                        self.default_foreground_color = fg;
                    }
                }

                if (state.terminal.modes.get(.reverse_colors)) {
                    if (self.background_color) |*c| {
                        c.* = fg;
                    } else {
                        self.default_background_color = fg;
                    }

                    if (self.foreground_color) |*c| {
                        c.* = bg;
                    } else {
                        self.default_foreground_color = bg;
                    }
                }

                // Get the viewport pin so that we can compare it to the current.
                const viewport_pin = state.terminal.screen.pages.pin(.{ .viewport = .{} }).?;

                // We used to share terminal state, but we've since learned through
                // analysis that it is faster to copy the terminal state than to
                // hold the lock while rebuilding GPU cells.
                var screen_copy = try state.terminal.screen.clone(
                    self.alloc,
                    .{ .viewport = .{} },
                    null,
                );
                errdefer screen_copy.deinit();

                // Whether to draw our cursor or not.
                const cursor_style = if (state.terminal.flags.password_input)
                    .lock
                else
                    renderer.cursorStyle(
                        state,
                        self.focused,
                        cursor_blink_visible,
                    );

                // Get our preedit state
                const preedit: ?renderer.State.Preedit = preedit: {
                    if (cursor_style == null) break :preedit null;
                    const p = state.preedit orelse break :preedit null;
                    break :preedit try p.clone(self.alloc);
                };
                errdefer if (preedit) |p| p.deinit(self.alloc);

                // If we have Kitty graphics data, we enter a SLOW SLOW SLOW path.
                // We only do this if the Kitty image state is dirty meaning only if
                // it changes.
                //
                // If we have any virtual references, we must also rebuild our
                // kitty state on every frame because any cell change can move
                // an image.
                if (state.terminal.screen.kitty_images.dirty or
                    self.image_virtual)
                {
                    try self.prepKittyGraphics(state.terminal);
                }

                // If we have any terminal dirty flags set then we need to rebuild
                // the entire screen. This can be optimized in the future.
                const full_rebuild: bool = rebuild: {
                    {
                        const Int = @typeInfo(terminal.Terminal.Dirty).@"struct".backing_integer.?;
                        const v: Int = @bitCast(state.terminal.flags.dirty);
                        if (v > 0) break :rebuild true;
                    }
                    {
                        const Int = @typeInfo(terminal.Screen.Dirty).@"struct".backing_integer.?;
                        const v: Int = @bitCast(state.terminal.screen.dirty);
                        if (v > 0) break :rebuild true;
                    }

                    // If our viewport changed then we need to rebuild the entire
                    // screen because it means we scrolled. If we have no previous
                    // viewport then we must rebuild.
                    const prev_viewport = self.cells_viewport orelse break :rebuild true;
                    if (!prev_viewport.eql(viewport_pin)) break :rebuild true;

                    break :rebuild false;
                };

                // Reset the dirty flags in the terminal and screen. We assume
                // that our rebuild will be successful since so we optimize for
                // success and reset while we hold the lock. This is much easier
                // than coordinating row by row or as changes are persisted.
                state.terminal.flags.dirty = .{};
                state.terminal.screen.dirty = .{};
                {
                    var it = state.terminal.screen.pages.pageIterator(
                        .right_down,
                        .{ .screen = .{} },
                        null,
                    );
                    while (it.next()) |chunk| {
                        var dirty_set = chunk.node.data.dirtyBitSet();
                        dirty_set.unsetAll();
                    }
                }

                // Update our viewport pin
                self.cells_viewport = viewport_pin;

                break :critical .{
                    .bg = self.background_color orelse self.default_background_color,
                    .screen = screen_copy,
                    .screen_type = state.terminal.active_screen,
                    .mouse = state.mouse,
                    .preedit = preedit,
                    .cursor_style = cursor_style,
                    .color_palette = state.terminal.color_palette.colors,
                    .full_rebuild = full_rebuild,
                };
            };
            defer {
                critical.screen.deinit();
                if (critical.preedit) |p| p.deinit(self.alloc);
            }

            // Build our GPU cells
            try self.rebuildCells(
                critical.full_rebuild,
                &critical.screen,
                critical.screen_type,
                critical.mouse,
                critical.preedit,
                critical.cursor_style,
                &critical.color_palette,
            );

            // Notify our shaper we're done for the frame. For some shapers,
            // such as CoreText, this triggers off-thread cleanup logic.
            self.font_shaper.endFrame();

            // Acquire the draw mutex because we're modifying state here.
            {
                self.draw_mutex.lock();
                defer self.draw_mutex.unlock();

                // Update our background color
                self.uniforms.bg_color = .{
                    critical.bg.r,
                    critical.bg.g,
                    critical.bg.b,
                    @intFromFloat(@round(self.config.background_opacity * 255.0)),
                };
            }
        }

        /// Draw the frame to the screen.
        ///
        /// If `sync` is true, this will synchronously block until
        /// the frame is finished drawing and has been presented.
        pub fn drawFrame(
            self: *Self,
            sync: bool,
        ) !void {
            // We hold a the draw mutex to prevent changes to any
            // data we access while we're in the middle of drawing.
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            // Let our graphics API do any bookkeeping, etc.
            // that it needs to do before / after `drawFrame`.
            self.api.drawFrameStart();
            defer self.api.drawFrameEnd();

            // Retrieve the most up-to-date surface size from the Graphics API
            const surface_size = try self.api.surfaceSize();

            // If either of our surface dimensions is zero
            // then drawing is absurd, so we just return.
            if (surface_size.width == 0 or surface_size.height == 0) return;

            const size_changed =
                self.size.screen.width != surface_size.width or
                self.size.screen.height != surface_size.height;

            // Conditions under which we need to draw the frame, otherwise we
            // don't need to since the previous frame should be identical.
            const needs_redraw =
                size_changed or
                self.cells_rebuilt or
                self.hasAnimations() or
                sync;

            if (!needs_redraw) {
                // We still need to present the last target again, because the
                // apprt may be swapping buffers and display an outdated frame
                // if we don't draw something new.
                try self.api.presentLastTarget();
                return;
            }
            self.cells_rebuilt = false;

            // Wait for a frame to be available.
            const frame = try self.swap_chain.nextFrame();
            errdefer self.swap_chain.releaseFrame();
            // log.debug("drawing frame index={}", .{self.swap_chain.frame_index});

            // If we need to reinitialize our shaders, do so.
            if (self.reinitialize_shaders) {
                self.reinitialize_shaders = false;
                self.shaders.deinit(self.alloc);
                try self.initShaders();
            }

            // Our shaders should not be defunct at this point.
            assert(!self.shaders.defunct);

            // If we have custom shaders, make sure we have the
            // custom shader state in our frame state, otherwise
            // if we have a state but don't need it we remove it.
            if (self.has_custom_shaders) {
                if (frame.custom_shader_state == null) {
                    frame.custom_shader_state = try .init(self.api);
                    try frame.custom_shader_state.?.resize(
                        self.api,
                        surface_size.width,
                        surface_size.height,
                    );
                }
            } else if (frame.custom_shader_state) |*state| {
                state.deinit();
                frame.custom_shader_state = null;
            }

            // If our stored size doesn't match the
            // surface size we need to update it.
            if (size_changed) {
                self.size.screen = .{
                    .width = surface_size.width,
                    .height = surface_size.height,
                };
                self.updateScreenSizeUniforms();
            }

            // If this frame's target isn't the correct size, or the target
            // config has changed (such as when the blending mode changes),
            // remove it and replace it with a new one with the right values.
            if (frame.target.width != self.size.screen.width or
                frame.target.height != self.size.screen.height or
                frame.target_config_modified != self.target_config_modified)
            {
                try frame.resize(
                    self.api,
                    self.size.screen.width,
                    self.size.screen.height,
                );
                frame.target_config_modified = self.target_config_modified;
            }

            // Upload images to the GPU as necessary.
            {
                var image_it = self.images.iterator();
                while (image_it.next()) |kv| {
                    switch (kv.value_ptr.image) {
                        .ready => {},

                        .pending_gray,
                        .pending_gray_alpha,
                        .pending_rgb,
                        .pending_rgba,
                        .replace_gray,
                        .replace_gray_alpha,
                        .replace_rgb,
                        .replace_rgba,
                        => try kv.value_ptr.image.upload(self.alloc, &self.api),

                        .unload_pending,
                        .unload_replace,
                        .unload_ready,
                        => {
                            kv.value_ptr.image.deinit(self.alloc);
                            self.images.removeByPtr(kv.key_ptr);
                        },
                    }
                }
            }

            // Setup our frame data
            try frame.uniforms.sync(&.{self.uniforms});
            try frame.cells_bg.sync(self.cells.bg_cells);
            const fg_count = try frame.cells.syncFromArrayLists(self.cells.fg_rows.lists);

            // If we have custom shaders, update the animation time.
            if (frame.custom_shader_state) |*state| {
                const now = std.time.Instant.now() catch state.first_frame_time;
                const since_ns: f32 = @floatFromInt(now.since(state.first_frame_time));
                const delta_ns: f32 = @floatFromInt(now.since(state.last_frame_time));
                state.uniforms.time = since_ns / std.time.ns_per_s;
                state.uniforms.time_delta = delta_ns / std.time.ns_per_s;
                state.last_frame_time = now;
            }

            // If our font atlas changed, sync the texture data
            texture: {
                const modified = self.font_grid.atlas_grayscale.modified.load(.monotonic);
                if (modified <= frame.grayscale_modified) break :texture;
                self.font_grid.lock.lockShared();
                defer self.font_grid.lock.unlockShared();
                frame.grayscale_modified = self.font_grid.atlas_grayscale.modified.load(.monotonic);
                try self.syncAtlasTexture(&self.font_grid.atlas_grayscale, &frame.grayscale);
            }
            texture: {
                const modified = self.font_grid.atlas_color.modified.load(.monotonic);
                if (modified <= frame.color_modified) break :texture;
                self.font_grid.lock.lockShared();
                defer self.font_grid.lock.unlockShared();
                frame.color_modified = self.font_grid.atlas_color.modified.load(.monotonic);
                try self.syncAtlasTexture(&self.font_grid.atlas_color, &frame.color);
            }

            // Get a frame context from the graphics API.
            var frame_ctx = try self.api.beginFrame(self, &frame.target);
            defer frame_ctx.complete(sync);

            {
                var pass = frame_ctx.renderPass(&.{.{
                    .target = if (frame.custom_shader_state) |state|
                        .{ .texture = state.back_texture }
                    else
                        .{ .target = frame.target },
                    .clear_color = .{ 0.0, 0.0, 0.0, 0.0 },
                }});
                defer pass.complete();

                // bg images
                try self.drawImagePlacements(&pass, self.image_placements.items[0..self.image_bg_end]);
                // bg
                pass.step(.{
                    .pipeline = self.shaders.cell_bg_pipeline,
                    .uniforms = frame.uniforms.buffer,
                    .buffers = &.{ null, frame.cells_bg.buffer },
                    .draw = .{
                        .type = .triangle,
                        .vertex_count = 3,
                    },
                });
                // mg images
                try self.drawImagePlacements(&pass, self.image_placements.items[self.image_bg_end..self.image_text_end]);
                // text
                pass.step(.{
                    .pipeline = self.shaders.cell_text_pipeline,
                    .uniforms = frame.uniforms.buffer,
                    .buffers = &.{
                        frame.cells.buffer,
                        frame.cells_bg.buffer,
                    },
                    .textures = &.{
                        frame.grayscale,
                        frame.color,
                    },
                    .draw = .{
                        .type = .triangle_strip,
                        .vertex_count = 4,
                        .instance_count = fg_count,
                    },
                });
                // fg images
                try self.drawImagePlacements(&pass, self.image_placements.items[self.image_text_end..]);
            }

            // If we have custom shaders, then we render them.
            if (frame.custom_shader_state) |*state| {
                // We create a buffer on the GPU for our post uniforms.
                // TODO: This should be a part of the frame state tbqh.
                const PostBuffer = Buffer(shaderpkg.PostUniforms);
                const uniform_buffer = try PostBuffer.initFill(
                    self.api.bufferOptions(),
                    &.{state.uniforms},
                );
                defer uniform_buffer.deinit();

                for (self.shaders.post_pipelines, 0..) |pipeline, i| {
                    defer state.swap();

                    var pass = frame_ctx.renderPass(&.{.{
                        .target = if (i < self.shaders.post_pipelines.len - 1)
                            .{ .texture = state.front_texture }
                        else
                            .{ .target = frame.target },
                        .clear_color = .{ 0.0, 0.0, 0.0, 0.0 },
                    }});
                    defer pass.complete();

                    pass.step(.{
                        .pipeline = pipeline,
                        .uniforms = uniform_buffer.buffer,
                        .textures = &.{state.back_texture},
                        .draw = .{
                            .type = .triangle,
                            .vertex_count = 3,
                        },
                    });
                }
            }
        }

        // Callback from the graphics API when a frame is completed.
        pub fn frameCompleted(
            self: *Self,
            health: Health,
        ) void {
            // If our health value hasn't changed, then we do nothing. We don't
            // do a cmpxchg here because strict atomicity isn't important.
            if (self.health.load(.seq_cst) != health) {
                self.health.store(health, .seq_cst);

                // Our health value changed, so we notify the surface so that it
                // can do something about it.
                _ = self.surface_mailbox.push(.{
                    .renderer_health = health,
                }, .{ .forever = {} });
            }

            // Always release our semaphore
            self.swap_chain.releaseFrame();
        }

        fn drawImagePlacements(
            self: *Self,
            pass: *RenderPass,
            placements: []const imagepkg.Placement,
        ) !void {
            if (placements.len == 0) return;

            for (placements) |p| {

                // Look up the image
                const image = self.images.get(p.image_id) orelse {
                    log.warn("image not found for placement image_id={}", .{p.image_id});
                    return;
                };

                // Get the texture
                const texture = switch (image.image) {
                    .ready => |t| t,
                    else => {
                        log.warn("image not ready for placement image_id={}", .{p.image_id});
                        return;
                    },
                };

                // Create our vertex buffer, which is always exactly one item.
                // future(mitchellh): we can group rendering multiple instances of a single image
                var buf = try Buffer(shaderpkg.Image).initFill(
                    self.api.imageBufferOptions(),
                    &.{.{
                        .grid_pos = .{
                            @as(f32, @floatFromInt(p.x)),
                            @as(f32, @floatFromInt(p.y)),
                        },

                        .cell_offset = .{
                            @as(f32, @floatFromInt(p.cell_offset_x)),
                            @as(f32, @floatFromInt(p.cell_offset_y)),
                        },

                        .source_rect = .{
                            @as(f32, @floatFromInt(p.source_x)),
                            @as(f32, @floatFromInt(p.source_y)),
                            @as(f32, @floatFromInt(p.source_width)),
                            @as(f32, @floatFromInt(p.source_height)),
                        },

                        .dest_size = .{
                            @as(f32, @floatFromInt(p.width)),
                            @as(f32, @floatFromInt(p.height)),
                        },
                    }},
                );
                defer buf.deinit();

                pass.step(.{
                    .pipeline = self.shaders.image_pipeline,
                    .buffers = &.{buf.buffer},
                    .textures = &.{texture},
                    .draw = .{
                        .type = .triangle_strip,
                        .vertex_count = 4,
                    },
                });
            }
        }

        /// This goes through the Kitty graphic placements and accumulates the
        /// placements we need to render on our viewport. It also ensures that
        /// the visible images are loaded on the GPU.
        fn prepKittyGraphics(
            self: *Self,
            t: *terminal.Terminal,
        ) !void {
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            const storage = &t.screen.kitty_images;
            defer storage.dirty = false;

            // We always clear our previous placements no matter what because
            // we rebuild them from scratch.
            self.image_placements.clearRetainingCapacity();
            self.image_virtual = false;

            // Go through our known images and if there are any that are no longer
            // in use then mark them to be freed.
            //
            // This never conflicts with the below because a placement can't
            // reference an image that doesn't exist.
            {
                var it = self.images.iterator();
                while (it.next()) |kv| {
                    if (storage.imageById(kv.key_ptr.*) == null) {
                        kv.value_ptr.image.markForUnload();
                    }
                }
            }

            // The top-left and bottom-right corners of our viewport in screen
            // points. This lets us determine offsets and containment of placements.
            const top = t.screen.pages.getTopLeft(.viewport);
            const bot = t.screen.pages.getBottomRight(.viewport).?;
            const top_y = t.screen.pages.pointFromPin(.screen, top).?.screen.y;
            const bot_y = t.screen.pages.pointFromPin(.screen, bot).?.screen.y;

            // Go through the placements and ensure the image is loaded on the GPU.
            var it = storage.placements.iterator();
            while (it.next()) |kv| {
                const p = kv.value_ptr;

                // Special logic based on location
                switch (p.location) {
                    .pin => {},
                    .virtual => {
                        // We need to mark virtual placements on our renderer so that
                        // we know to rebuild in more scenarios since cell changes can
                        // now trigger placement changes.
                        self.image_virtual = true;

                        // We also continue out because virtual placements are
                        // only triggered by the unicode placeholder, not by the
                        // placement itself.
                        continue;
                    },
                }

                // Get the image for the placement
                const image = storage.imageById(kv.key_ptr.image_id) orelse {
                    log.warn(
                        "missing image for placement, ignoring image_id={}",
                        .{kv.key_ptr.image_id},
                    );
                    continue;
                };

                try self.prepKittyPlacement(t, top_y, bot_y, &image, p);
            }

            // If we have virtual placements then we need to scan for placeholders.
            if (self.image_virtual) {
                var v_it = terminal.kitty.graphics.unicode.placementIterator(top, bot);
                while (v_it.next()) |virtual_p| try self.prepKittyVirtualPlacement(
                    t,
                    &virtual_p,
                );
            }

            // Sort the placements by their Z value.
            std.mem.sortUnstable(
                imagepkg.Placement,
                self.image_placements.items,
                {},
                struct {
                    fn lessThan(
                        ctx: void,
                        lhs: imagepkg.Placement,
                        rhs: imagepkg.Placement,
                    ) bool {
                        _ = ctx;
                        return lhs.z < rhs.z or (lhs.z == rhs.z and lhs.image_id < rhs.image_id);
                    }
                }.lessThan,
            );

            // Find our indices. The values are sorted by z so we can find the
            // first placement out of bounds to find the limits.
            var bg_end: ?u32 = null;
            var text_end: ?u32 = null;
            const bg_limit = std.math.minInt(i32) / 2;
            for (self.image_placements.items, 0..) |p, i| {
                if (bg_end == null and p.z >= bg_limit) {
                    bg_end = @intCast(i);
                }
                if (text_end == null and p.z >= 0) {
                    text_end = @intCast(i);
                }
            }

            self.image_bg_end = bg_end orelse 0;
            self.image_text_end = text_end orelse self.image_bg_end;
        }

        fn prepKittyVirtualPlacement(
            self: *Self,
            t: *terminal.Terminal,
            p: *const terminal.kitty.graphics.unicode.Placement,
        ) !void {
            const storage = &t.screen.kitty_images;
            const image = storage.imageById(p.image_id) orelse {
                log.warn(
                    "missing image for virtual placement, ignoring image_id={}",
                    .{p.image_id},
                );
                return;
            };

            const rp = p.renderPlacement(
                storage,
                &image,
                self.grid_metrics.cell_width,
                self.grid_metrics.cell_height,
            ) catch |err| {
                log.warn("error rendering virtual placement err={}", .{err});
                return;
            };

            // If our placement is zero sized then we don't do anything.
            if (rp.dest_width == 0 or rp.dest_height == 0) return;

            const viewport: terminal.point.Point = t.screen.pages.pointFromPin(
                .viewport,
                rp.top_left,
            ) orelse {
                // This is unreachable with virtual placements because we should
                // only ever be looking at virtual placements that are in our
                // viewport in the renderer and virtual placements only ever take
                // up one row.
                unreachable;
            };

            // Send our image to the GPU and store the placement for rendering.
            try self.prepKittyImage(&image);
            try self.image_placements.append(self.alloc, .{
                .image_id = image.id,
                .x = @intCast(rp.top_left.x),
                .y = @intCast(viewport.viewport.y),
                .z = -1,
                .width = rp.dest_width,
                .height = rp.dest_height,
                .cell_offset_x = rp.offset_x,
                .cell_offset_y = rp.offset_y,
                .source_x = rp.source_x,
                .source_y = rp.source_y,
                .source_width = rp.source_width,
                .source_height = rp.source_height,
            });
        }

        fn prepKittyPlacement(
            self: *Self,
            t: *terminal.Terminal,
            top_y: u32,
            bot_y: u32,
            image: *const terminal.kitty.graphics.Image,
            p: *const terminal.kitty.graphics.ImageStorage.Placement,
        ) !void {
            // Get the rect for the placement. If this placement doesn't have
            // a rect then its virtual or something so skip it.
            const rect = p.rect(image.*, t) orelse return;

            // This is expensive but necessary.
            const img_top_y = t.screen.pages.pointFromPin(.screen, rect.top_left).?.screen.y;
            const img_bot_y = t.screen.pages.pointFromPin(.screen, rect.bottom_right).?.screen.y;

            // If the selection isn't within our viewport then skip it.
            if (img_top_y > bot_y) return;
            if (img_bot_y < top_y) return;

            // We need to prep this image for upload if it isn't in the cache OR
            // it is in the cache but the transmit time doesn't match meaning this
            // image is different.
            try self.prepKittyImage(image);

            // Calculate the dimensions of our image, taking in to
            // account the rows / columns specified by the placement.
            const dest_size = p.calculatedSize(image.*, t);

            // Calculate the source rectangle
            const source_x = @min(image.width, p.source_x);
            const source_y = @min(image.height, p.source_y);
            const source_width = if (p.source_width > 0)
                @min(image.width - source_x, p.source_width)
            else
                image.width;
            const source_height = if (p.source_height > 0)
                @min(image.height - source_y, p.source_height)
            else
                image.height;

            // Get the viewport-relative Y position of the placement.
            const y_pos: i32 = @as(i32, @intCast(img_top_y)) - @as(i32, @intCast(top_y));

            // Accumulate the placement
            if (dest_size.width > 0 and dest_size.height > 0) {
                try self.image_placements.append(self.alloc, .{
                    .image_id = image.id,
                    .x = @intCast(rect.top_left.x),
                    .y = y_pos,
                    .z = p.z,
                    .width = dest_size.width,
                    .height = dest_size.height,
                    .cell_offset_x = p.x_offset,
                    .cell_offset_y = p.y_offset,
                    .source_x = source_x,
                    .source_y = source_y,
                    .source_width = source_width,
                    .source_height = source_height,
                });
            }
        }

        fn prepKittyImage(
            self: *Self,
            image: *const terminal.kitty.graphics.Image,
        ) !void {
            // If this image exists and its transmit time is the same we assume
            // it is the identical image so we don't need to send it to the GPU.
            const gop = try self.images.getOrPut(self.alloc, image.id);
            if (gop.found_existing and
                gop.value_ptr.transmit_time.order(image.transmit_time) == .eq)
            {
                return;
            }

            // Copy the data into the pending state.
            const data = try self.alloc.dupe(u8, image.data);
            errdefer self.alloc.free(data);

            // Store it in the map
            const pending: Image.Pending = .{
                .width = image.width,
                .height = image.height,
                .data = data.ptr,
            };

            const new_image: Image = switch (image.format) {
                .gray => .{ .pending_gray = pending },
                .gray_alpha => .{ .pending_gray_alpha = pending },
                .rgb => .{ .pending_rgb = pending },
                .rgba => .{ .pending_rgba = pending },
                .png => unreachable, // should be decoded by now
            };

            if (!gop.found_existing) {
                gop.value_ptr.* = .{
                    .image = new_image,
                    .transmit_time = undefined,
                };
            } else {
                try gop.value_ptr.image.markForReplace(
                    self.alloc,
                    new_image,
                );
            }

            gop.value_ptr.transmit_time = image.transmit_time;
        }

        /// Update the configuration.
        pub fn changeConfig(self: *Self, config: *DerivedConfig) !void {
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            // We always redo the font shaper in case font features changed. We
            // could check to see if there was an actual config change but this is
            // easier and rare enough to not cause performance issues.
            {
                var font_shaper = try font.Shaper.init(self.alloc, .{
                    .features = config.font_features.items,
                });
                errdefer font_shaper.deinit();
                self.font_shaper.deinit();
                self.font_shaper = font_shaper;
            }

            // We also need to reset the shaper cache so shaper info
            // from the previous font isn't re-used for the new font.
            const font_shaper_cache = font.ShaperCache.init();
            self.font_shaper_cache.deinit(self.alloc);
            self.font_shaper_cache = font_shaper_cache;

            // Set our new minimum contrast
            self.uniforms.min_contrast = config.min_contrast;

            // Set our new color space and blending
            self.uniforms.bools.use_display_p3 = config.colorspace == .@"display-p3";
            self.uniforms.bools.use_linear_blending = config.blending.isLinear();
            self.uniforms.bools.use_linear_correction = config.blending == .@"linear-corrected";

            // Set our new colors
            self.default_background_color = config.background;
            self.default_foreground_color = config.foreground;
            self.default_cursor_color = if (!config.cursor_invert) config.cursor_color else null;
            self.cursor_invert = config.cursor_invert;

            const old_blending = self.config.blending;
            const custom_shaders_changed = !self.config.custom_shaders.equal(config.custom_shaders);

            self.config.deinit();
            self.config = config.*;

            // Reset our viewport to force a rebuild, in case of a font change.
            self.cells_viewport = null;

            const blending_changed = old_blending != config.blending;

            if (blending_changed) {
                // We update our API's blending mode.
                self.api.blending = config.blending;
                // And indicate that we need to reinitialize our shaders.
                self.reinitialize_shaders = true;
                // And indicate that our swap chain targets need to
                // be re-created to account for the new blending mode.
                self.target_config_modified +%= 1;
            }

            if (custom_shaders_changed) {
                self.reinitialize_shaders = true;
            }
        }

        /// Resize the screen.
        pub fn setScreenSize(
            self: *Self,
            size: renderer.Size,
        ) void {
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            // We only actually need the padding from this,
            // everything else is derived elsewhere.
            self.size.padding = size.padding;

            self.updateScreenSizeUniforms();

            log.debug("screen size size={}", .{size});
        }

        /// Update uniforms that are based on the screen size.
        ///
        /// Caller must hold the draw mutex.
        fn updateScreenSizeUniforms(self: *Self) void {
            const terminal_size = self.size.terminal();

            // Blank space around the grid.
            const blank: renderer.Padding = self.size.screen.blankPadding(
                self.size.padding,
                .{
                    .columns = self.cells.size.columns,
                    .rows = self.cells.size.rows,
                },
                .{
                    .width = self.grid_metrics.cell_width,
                    .height = self.grid_metrics.cell_height,
                },
            ).add(self.size.padding);

            // Setup our uniforms
            self.uniforms.projection_matrix = math.ortho2d(
                -1 * @as(f32, @floatFromInt(self.size.padding.left)),
                @floatFromInt(terminal_size.width + self.size.padding.right),
                @floatFromInt(terminal_size.height + self.size.padding.bottom),
                -1 * @as(f32, @floatFromInt(self.size.padding.top)),
            );
            self.uniforms.grid_padding = .{
                @floatFromInt(blank.top),
                @floatFromInt(blank.right),
                @floatFromInt(blank.bottom),
                @floatFromInt(blank.left),
            };
        }

        /// Convert the terminal state to GPU cells stored in CPU memory. These
        /// are then synced to the GPU in the next frame. This only updates CPU
        /// memory and doesn't touch the GPU.
        fn rebuildCells(
            self: *Self,
            wants_rebuild: bool,
            screen: *terminal.Screen,
            screen_type: terminal.ScreenType,
            mouse: renderer.State.Mouse,
            preedit: ?renderer.State.Preedit,
            cursor_style_: ?renderer.CursorStyle,
            color_palette: *const terminal.color.Palette,
        ) !void {
            self.draw_mutex.lock();
            defer self.draw_mutex.unlock();

            // const start = try std.time.Instant.now();
            // const start_micro = std.time.microTimestamp();
            // defer {
            //     const end = std.time.Instant.now() catch unreachable;
            //     // "[rebuildCells time] <START us>\t<TIME_TAKEN us>"
            //     std.log.warn("[rebuildCells time] {}\t{}", .{start_micro, end.since(start) / std.time.ns_per_us});
            // }

            _ = screen_type; // we might use this again later so not deleting it yet

            // Create an arena for all our temporary allocations while rebuilding
            var arena = ArenaAllocator.init(self.alloc);
            defer arena.deinit();
            const arena_alloc = arena.allocator();

            // Create our match set for the links.
            var link_match_set: link.MatchSet = if (mouse.point) |mouse_pt| try self.config.links.matchSet(
                arena_alloc,
                screen,
                mouse_pt,
                mouse.mods,
            ) else .{};

            // Determine our x/y range for preedit. We don't want to render anything
            // here because we will render the preedit separately.
            const preedit_range: ?struct {
                y: terminal.size.CellCountInt,
                x: [2]terminal.size.CellCountInt,
                cp_offset: usize,
            } = if (preedit) |preedit_v| preedit: {
                const range = preedit_v.range(screen.cursor.x, screen.pages.cols - 1);
                break :preedit .{
                    .y = screen.cursor.y,
                    .x = .{ range.start, range.end },
                    .cp_offset = range.cp_offset,
                };
            } else null;

            const grid_size_diff =
                self.cells.size.rows != screen.pages.rows or
                self.cells.size.columns != screen.pages.cols;

            if (grid_size_diff) {
                var new_size = self.cells.size;
                new_size.rows = screen.pages.rows;
                new_size.columns = screen.pages.cols;
                try self.cells.resize(self.alloc, new_size);

                // Update our uniforms accordingly, otherwise
                // our background cells will be out of place.
                self.uniforms.grid_size = .{ new_size.columns, new_size.rows };
            }

            const rebuild = wants_rebuild or grid_size_diff;

            if (rebuild) {
                // If we are doing a full rebuild, then we clear the entire cell buffer.
                self.cells.reset();

                // We also reset our padding extension depending on the screen type
                switch (self.config.padding_color) {
                    .background => {},

                    // For extension, assume we are extending in all directions.
                    // For "extend" this may be disabled due to heuristics below.
                    .extend, .@"extend-always" => {
                        self.uniforms.padding_extend = .{
                            .up = true,
                            .down = true,
                            .left = true,
                            .right = true,
                        };
                    },
                }
            }

            // We rebuild the cells row-by-row because we
            // do font shaping and dirty tracking by row.
            var row_it = screen.pages.rowIterator(.left_up, .{ .viewport = .{} }, null);
            // If our cell contents buffer is shorter than the screen viewport,
            // we render the rows that fit, starting from the bottom. If instead
            // the viewport is shorter than the cell contents buffer, we align
            // the top of the viewport with the top of the contents buffer.
            var y: terminal.size.CellCountInt = @min(
                screen.pages.rows,
                self.cells.size.rows,
            );
            while (row_it.next()) |row| {
                // The viewport may have more rows than our cell contents,
                // so we need to break from the loop early if we hit y = 0.
                if (y == 0) break;

                y -= 1;

                if (!rebuild) {
                    // Only rebuild if we are doing a full rebuild or this row is dirty.
                    if (!row.isDirty()) continue;

                    // Clear the cells if the row is dirty
                    self.cells.clear(y);
                }

                // True if we want to do font shaping around the cursor.
                // We want to do font shaping as long as the cursor is enabled.
                const shape_cursor = screen.viewportIsBottom() and
                    y == screen.cursor.y;

                // We need to get this row's selection, if
                // there is one, for proper run splitting.
                const row_selection = sel: {
                    const sel = screen.selection orelse break :sel null;
                    const pin = screen.pages.pin(.{ .viewport = .{ .y = y } }) orelse
                        break :sel null;
                    break :sel sel.containedRow(screen, pin) orelse null;
                };

                // On primary screen, we still apply vertical padding
                // extension under certain conditions we feel are safe.
                //
                // This helps make some scenarios look better while
                // avoiding scenarios we know do NOT look good.
                switch (self.config.padding_color) {
                    // These already have the correct values set above.
                    .background, .@"extend-always" => {},

                    // Apply heuristics for padding extension.
                    .extend => if (y == 0) {
                        self.uniforms.padding_extend.up = !row.neverExtendBg(
                            color_palette,
                            self.background_color orelse self.default_background_color,
                        );
                    } else if (y == self.cells.size.rows - 1) {
                        self.uniforms.padding_extend.down = !row.neverExtendBg(
                            color_palette,
                            self.background_color orelse self.default_background_color,
                        );
                    },
                }

                // Iterator of runs for shaping.
                var run_iter = self.font_shaper.runIterator(
                    self.font_grid,
                    screen,
                    row,
                    row_selection,
                    if (shape_cursor) screen.cursor.x else null,
                );
                var shaper_run: ?font.shape.TextRun = try run_iter.next(self.alloc);
                var shaper_cells: ?[]const font.shape.Cell = null;
                var shaper_cells_i: usize = 0;

                const row_cells_all = row.cells(.all);

                // If our viewport is wider than our cell contents buffer,
                // we still only process cells up to the width of the buffer.
                const row_cells = row_cells_all[0..@min(row_cells_all.len, self.cells.size.columns)];

                for (row_cells, 0..) |*cell, x| {
                    // If this cell falls within our preedit range then we
                    // skip this because preedits are setup separately.
                    if (preedit_range) |range| preedit: {
                        // We're not on the preedit line, no actions necessary.
                        if (range.y != y) break :preedit;
                        // We're before the preedit range, no actions necessary.
                        if (x < range.x[0]) break :preedit;
                        // We're in the preedit range, skip this cell.
                        if (x <= range.x[1]) continue;
                        // After exiting the preedit range we need to catch
                        // the run position up because of the missed cells.
                        // In all other cases, no action is necessary.
                        if (x != range.x[1] + 1) break :preedit;

                        // Step the run iterator until we find a run that ends
                        // after the current cell, which will be the soonest run
                        // that might contain glyphs for our cell.
                        while (shaper_run) |run| {
                            if (run.offset + run.cells > x) break;
                            shaper_run = try run_iter.next(self.alloc);
                            shaper_cells = null;
                            shaper_cells_i = 0;
                        }

                        const run = shaper_run orelse break :preedit;

                        // If we haven't shaped this run, do so now.
                        shaper_cells = shaper_cells orelse
                            // Try to read the cells from the shaping cache if we can.
                            self.font_shaper_cache.get(run) orelse
                            cache: {
                                // Otherwise we have to shape them.
                                const cells = try self.font_shaper.shape(run);

                                // Try to cache them. If caching fails for any reason we
                                // continue because it is just a performance optimization,
                                // not a correctness issue.
                                self.font_shaper_cache.put(
                                    self.alloc,
                                    run,
                                    cells,
                                ) catch |err| {
                                    log.warn(
                                        "error caching font shaping results err={}",
                                        .{err},
                                    );
                                };

                                // The cells we get from direct shaping are always owned
                                // by the shaper and valid until the next shaping call so
                                // we can safely use them.
                                break :cache cells;
                            };

                        // Advance our index until we reach or pass
                        // our current x position in the shaper cells.
                        while (shaper_cells.?[shaper_cells_i].x < x) {
                            shaper_cells_i += 1;
                        }
                    }

                    const wide = cell.wide;

                    const style = row.style(cell);

                    const cell_pin: terminal.Pin = cell: {
                        var copy = row;
                        copy.x = @intCast(x);
                        break :cell copy;
                    };

                    // True if this cell is selected
                    const selected: bool = if (screen.selection) |sel|
                        sel.contains(screen, .{
                            .node = row.node,
                            .y = row.y,
                            .x = @intCast(
                                // Spacer tails should show the selection
                                // state of the wide cell they belong to.
                                if (wide == .spacer_tail)
                                    x -| 1
                                else
                                    x,
                            ),
                        })
                    else
                        false;

                    const bg_style = style.bg(cell, color_palette);
                    const fg_style = style.fg(color_palette, self.config.bold_is_bright) orelse self.foreground_color orelse self.default_foreground_color;

                    // The final background color for the cell.
                    const bg = bg: {
                        if (selected) {
                            break :bg if (self.config.invert_selection_fg_bg)
                                if (style.flags.inverse)
                                    // Cell is selected with invert selection fg/bg
                                    // enabled, and the cell has the inverse style
                                    // flag, so they cancel out and we get the normal
                                    // bg color.
                                    bg_style
                                else
                                    // If it doesn't have the inverse style
                                    // flag then we use the fg color instead.
                                    fg_style
                            else
                                // If we don't have invert selection fg/bg set then we
                                // just use the selection background if set, otherwise
                                // the default fg color.
                                break :bg self.config.selection_background orelse self.foreground_color orelse self.default_foreground_color;
                        }

                        // Not selected
                        break :bg if (style.flags.inverse != isCovering(cell.codepoint()))
                            // Two cases cause us to invert (use the fg color as the bg)
                            // - The "inverse" style flag.
                            // - A "covering" glyph; we use fg for bg in that
                            //   case to help make sure that padding extension
                            //   works correctly.
                            //
                            // If one of these is true (but not the other)
                            // then we use the fg style color for the bg.
                            fg_style
                        else
                            // Otherwise they cancel out.
                            bg_style;
                    };

                    const fg = fg: {
                        if (selected and !self.config.invert_selection_fg_bg) {
                            // If we don't have invert selection fg/bg set
                            // then we just use the selection foreground if
                            // set, otherwise the default bg color.
                            break :fg self.config.selection_foreground orelse self.background_color orelse self.default_background_color;
                        }

                        // Whether we need to use the bg color as our fg color:
                        // - Cell is inverted and not selected
                        // - Cell is selected and not inverted
                        //    Note: if selected then invert sel fg / bg must be
                        //    false since we separately handle it if true above.
                        break :fg if (style.flags.inverse != selected)
                            bg_style orelse self.background_color orelse self.default_background_color
                        else
                            fg_style;
                    };

                    // Foreground alpha for this cell.
                    const alpha: u8 = if (style.flags.faint) 175 else 255;

                    // Set the cell's background color.
                    {
                        const rgb = bg orelse self.background_color orelse self.default_background_color;

                        // Determine our background alpha. If we have transparency configured
                        // then this is dynamic depending on some situations. This is all
                        // in an attempt to make transparency look the best for various
                        // situations. See inline comments.
                        const bg_alpha: u8 = bg_alpha: {
                            const default: u8 = 255;

                            if (self.config.background_opacity >= 1) break :bg_alpha default;

                            // Cells that are selected should be fully opaque.
                            if (selected) break :bg_alpha default;

                            // Cells that are reversed should be fully opaque.
                            if (style.flags.inverse) break :bg_alpha default;

                            // Cells that have an explicit bg color should be fully opaque.
                            if (bg_style != null) {
                                break :bg_alpha default;
                            }

                            // Otherwise, we use the configured background opacity.
                            break :bg_alpha @intFromFloat(@round(self.config.background_opacity * 255.0));
                        };

                        self.cells.bgCell(y, x).* = .{
                            rgb.r, rgb.g, rgb.b, bg_alpha,
                        };
                    }

                    // If the invisible flag is set on this cell then we
                    // don't need to render any foreground elements, so
                    // we just skip all glyphs with this x coordinate.
                    //
                    // NOTE: This behavior matches xterm. Some other terminal
                    // emulators, e.g. Alacritty, still render text decorations
                    // and only make the text itself invisible. The decision
                    // has been made here to match xterm's behavior for this.
                    if (style.flags.invisible) {
                        continue;
                    }

                    // Give links a single underline, unless they already have
                    // an underline, in which case use a double underline to
                    // distinguish them.
                    const underline: terminal.Attribute.Underline = if (link_match_set.contains(screen, cell_pin))
                        if (style.flags.underline == .single)
                            .double
                        else
                            .single
                    else
                        style.flags.underline;

                    // We draw underlines first so that they layer underneath text.
                    // This improves readability when a colored underline is used
                    // which intersects parts of the text (descenders).
                    if (underline != .none) self.addUnderline(
                        @intCast(x),
                        @intCast(y),
                        underline,
                        style.underlineColor(color_palette) orelse fg,
                        alpha,
                    ) catch |err| {
                        log.warn(
                            "error adding underline to cell, will be invalid x={} y={}, err={}",
                            .{ x, y, err },
                        );
                    };

                    if (style.flags.overline) self.addOverline(@intCast(x), @intCast(y), fg, alpha) catch |err| {
                        log.warn(
                            "error adding overline to cell, will be invalid x={} y={}, err={}",
                            .{ x, y, err },
                        );
                    };

                    // If we're at or past the end of our shaper run then
                    // we need to get the next run from the run iterator.
                    if (shaper_cells != null and shaper_cells_i >= shaper_cells.?.len) {
                        shaper_run = try run_iter.next(self.alloc);
                        shaper_cells = null;
                        shaper_cells_i = 0;
                    }

                    if (shaper_run) |run| glyphs: {
                        // If we haven't shaped this run yet, do so.
                        shaper_cells = shaper_cells orelse
                            // Try to read the cells from the shaping cache if we can.
                            self.font_shaper_cache.get(run) orelse
                            cache: {
                                // Otherwise we have to shape them.
                                const cells = try self.font_shaper.shape(run);

                                // Try to cache them. If caching fails for any reason we
                                // continue because it is just a performance optimization,
                                // not a correctness issue.
                                self.font_shaper_cache.put(
                                    self.alloc,
                                    run,
                                    cells,
                                ) catch |err| {
                                    log.warn(
                                        "error caching font shaping results err={}",
                                        .{err},
                                    );
                                };

                                // The cells we get from direct shaping are always owned
                                // by the shaper and valid until the next shaping call so
                                // we can safely use them.
                                break :cache cells;
                            };

                        const cells = shaper_cells orelse break :glyphs;

                        // If there are no shaper cells for this run, ignore it.
                        // This can occur for runs of empty cells, and is fine.
                        if (cells.len == 0) break :glyphs;

                        // If we encounter a shaper cell to the left of the current
                        // cell then we have some problems. This logic relies on x
                        // position monotonically increasing.
                        assert(cells[shaper_cells_i].x >= x);

                        // NOTE: An assumption is made here that a single cell will never
                        // be present in more than one shaper run. If that assumption is
                        // violated, this logic breaks.

                        while (shaper_cells_i < cells.len and cells[shaper_cells_i].x == x) : ({
                            shaper_cells_i += 1;
                        }) {
                            self.addGlyph(
                                @intCast(x),
                                @intCast(y),
                                cell_pin,
                                cells[shaper_cells_i],
                                shaper_run.?,
                                fg,
                                alpha,
                            ) catch |err| {
                                log.warn(
                                    "error adding glyph to cell, will be invalid x={} y={}, err={}",
                                    .{ x, y, err },
                                );
                            };
                        }
                    }

                    // Finally, draw a strikethrough if necessary.
                    if (style.flags.strikethrough) self.addStrikethrough(
                        @intCast(x),
                        @intCast(y),
                        fg,
                        alpha,
                    ) catch |err| {
                        log.warn(
                            "error adding strikethrough to cell, will be invalid x={} y={}, err={}",
                            .{ x, y, err },
                        );
                    };
                }
            }

            // Setup our cursor rendering information.
            cursor: {
                // By default, we don't handle cursor inversion on the shader.
                self.cells.setCursor(null);
                self.uniforms.cursor_pos = .{
                    std.math.maxInt(u16),
                    std.math.maxInt(u16),
                };

                // If we have preedit text, we don't setup a cursor
                if (preedit != null) break :cursor;

                // Prepare the cursor cell contents.
                const style = cursor_style_ orelse break :cursor;
                const cursor_color = self.cursor_color orelse self.default_cursor_color orelse color: {
                    if (self.cursor_invert) {
                        // Use the foreground color from the cell under the cursor, if any.
                        const sty = screen.cursor.page_pin.style(screen.cursor.page_cell);
                        break :color if (sty.flags.inverse)
                            // If the cell is reversed, use background color instead.
                            (sty.bg(screen.cursor.page_cell, color_palette) orelse self.background_color orelse self.default_background_color)
                        else
                            (sty.fg(color_palette, self.config.bold_is_bright) orelse self.foreground_color orelse self.default_foreground_color);
                    } else {
                        break :color self.foreground_color orelse self.default_foreground_color;
                    }
                };

                self.addCursor(screen, style, cursor_color);

                // If the cursor is visible then we set our uniforms.
                if (style == .block and screen.viewportIsBottom()) {
                    const wide = screen.cursor.page_cell.wide;

                    self.uniforms.cursor_pos = .{
                        // If we are a spacer tail of a wide cell, our cursor needs
                        // to move back one cell. The saturate is to ensure we don't
                        // overflow but this shouldn't happen with well-formed input.
                        switch (wide) {
                            .narrow, .spacer_head, .wide => screen.cursor.x,
                            .spacer_tail => screen.cursor.x -| 1,
                        },
                        screen.cursor.y,
                    };

                    self.uniforms.bools.cursor_wide = switch (wide) {
                        .narrow, .spacer_head => false,
                        .wide, .spacer_tail => true,
                    };

                    const uniform_color = if (self.cursor_invert) blk: {
                        // Use the background color from the cell under the cursor, if any.
                        const sty = screen.cursor.page_pin.style(screen.cursor.page_cell);
                        break :blk if (sty.flags.inverse)
                            // If the cell is reversed, use foreground color instead.
                            (sty.fg(color_palette, self.config.bold_is_bright) orelse self.foreground_color orelse self.default_foreground_color)
                        else
                            (sty.bg(screen.cursor.page_cell, color_palette) orelse self.background_color orelse self.default_background_color);
                    } else if (self.config.cursor_text) |txt|
                        txt
                    else
                        self.background_color orelse self.default_background_color;

                    self.uniforms.cursor_color = .{
                        uniform_color.r,
                        uniform_color.g,
                        uniform_color.b,
                        255,
                    };
                }
            }

            // Setup our preedit text.
            if (preedit) |preedit_v| {
                const range = preedit_range.?;
                var x = range.x[0];
                for (preedit_v.codepoints[range.cp_offset..]) |cp| {
                    self.addPreeditCell(cp, .{ .x = x, .y = range.y }) catch |err| {
                        log.warn("error building preedit cell, will be invalid x={} y={}, err={}", .{
                            x,
                            range.y,
                            err,
                        });
                    };

                    x += if (cp.wide) 2 else 1;
                }
            }

            // Update that our cells rebuilt
            self.cells_rebuilt = true;

            // Log some things
            // log.debug("rebuildCells complete cached_runs={}", .{
            //     self.font_shaper_cache.count(),
            // });
        }

        /// Add an underline decoration to the specified cell
        fn addUnderline(
            self: *Self,
            x: terminal.size.CellCountInt,
            y: terminal.size.CellCountInt,
            style: terminal.Attribute.Underline,
            color: terminal.color.RGB,
            alpha: u8,
        ) !void {
            const sprite: font.Sprite = switch (style) {
                .none => unreachable,
                .single => .underline,
                .double => .underline_double,
                .dotted => .underline_dotted,
                .dashed => .underline_dashed,
                .curly => .underline_curly,
            };

            const render = try self.font_grid.renderGlyph(
                self.alloc,
                font.sprite_index,
                @intFromEnum(sprite),
                .{
                    .cell_width = 1,
                    .grid_metrics = self.grid_metrics,
                },
            );

            try self.cells.add(self.alloc, .underline, .{
                .mode = .fg,
                .grid_pos = .{ @intCast(x), @intCast(y) },
                .constraint_width = 1,
                .color = .{ color.r, color.g, color.b, alpha },
                .glyph_pos = .{ render.glyph.atlas_x, render.glyph.atlas_y },
                .glyph_size = .{ render.glyph.width, render.glyph.height },
                .bearings = .{
                    @intCast(render.glyph.offset_x),
                    @intCast(render.glyph.offset_y),
                },
            });
        }

        /// Add a overline decoration to the specified cell
        fn addOverline(
            self: *Self,
            x: terminal.size.CellCountInt,
            y: terminal.size.CellCountInt,
            color: terminal.color.RGB,
            alpha: u8,
        ) !void {
            const render = try self.font_grid.renderGlyph(
                self.alloc,
                font.sprite_index,
                @intFromEnum(font.Sprite.overline),
                .{
                    .cell_width = 1,
                    .grid_metrics = self.grid_metrics,
                },
            );

            try self.cells.add(self.alloc, .overline, .{
                .mode = .fg,
                .grid_pos = .{ @intCast(x), @intCast(y) },
                .constraint_width = 1,
                .color = .{ color.r, color.g, color.b, alpha },
                .glyph_pos = .{ render.glyph.atlas_x, render.glyph.atlas_y },
                .glyph_size = .{ render.glyph.width, render.glyph.height },
                .bearings = .{
                    @intCast(render.glyph.offset_x),
                    @intCast(render.glyph.offset_y),
                },
            });
        }

        /// Add a strikethrough decoration to the specified cell
        fn addStrikethrough(
            self: *Self,
            x: terminal.size.CellCountInt,
            y: terminal.size.CellCountInt,
            color: terminal.color.RGB,
            alpha: u8,
        ) !void {
            const render = try self.font_grid.renderGlyph(
                self.alloc,
                font.sprite_index,
                @intFromEnum(font.Sprite.strikethrough),
                .{
                    .cell_width = 1,
                    .grid_metrics = self.grid_metrics,
                },
            );

            try self.cells.add(self.alloc, .strikethrough, .{
                .mode = .fg,
                .grid_pos = .{ @intCast(x), @intCast(y) },
                .constraint_width = 1,
                .color = .{ color.r, color.g, color.b, alpha },
                .glyph_pos = .{ render.glyph.atlas_x, render.glyph.atlas_y },
                .glyph_size = .{ render.glyph.width, render.glyph.height },
                .bearings = .{
                    @intCast(render.glyph.offset_x),
                    @intCast(render.glyph.offset_y),
                },
            });
        }

        // Add a glyph to the specified cell.
        fn addGlyph(
            self: *Self,
            x: terminal.size.CellCountInt,
            y: terminal.size.CellCountInt,
            cell_pin: terminal.Pin,
            shaper_cell: font.shape.Cell,
            shaper_run: font.shape.TextRun,
            color: terminal.color.RGB,
            alpha: u8,
        ) !void {
            const rac = cell_pin.rowAndCell();
            const cell = rac.cell;

            // Render
            const render = try self.font_grid.renderGlyph(
                self.alloc,
                shaper_run.font_index,
                shaper_cell.glyph_index,
                .{
                    .grid_metrics = self.grid_metrics,
                    .thicken = self.config.font_thicken,
                    .thicken_strength = self.config.font_thicken_strength,
                },
            );

            // If the glyph is 0 width or height, it will be invisible
            // when drawn, so don't bother adding it to the buffer.
            if (render.glyph.width == 0 or render.glyph.height == 0) {
                return;
            }

            const mode: shaderpkg.CellText.Mode = switch (try fgMode(
                render.presentation,
                cell_pin,
            )) {
                .normal => .fg,
                .color => .fg_color,
                .constrained => .fg_constrained,
                .powerline => .fg_powerline,
            };

            try self.cells.add(self.alloc, .text, .{
                .mode = mode,
                .grid_pos = .{ @intCast(x), @intCast(y) },
                .constraint_width = cell.gridWidth(),
                .color = .{ color.r, color.g, color.b, alpha },
                .glyph_pos = .{ render.glyph.atlas_x, render.glyph.atlas_y },
                .glyph_size = .{ render.glyph.width, render.glyph.height },
                .bearings = .{
                    @intCast(render.glyph.offset_x + shaper_cell.x_offset),
                    @intCast(render.glyph.offset_y + shaper_cell.y_offset),
                },
            });
        }

        fn addCursor(
            self: *Self,
            screen: *terminal.Screen,
            cursor_style: renderer.CursorStyle,
            cursor_color: terminal.color.RGB,
        ) void {
            // Add the cursor. We render the cursor over the wide character if
            // we're on the wide character tail.
            const wide, const x = cell: {
                // The cursor goes over the screen cursor position.
                const cell = screen.cursor.page_cell;
                if (cell.wide != .spacer_tail or screen.cursor.x == 0)
                    break :cell .{ cell.wide == .wide, screen.cursor.x };

                // If we're part of a wide character, we move the cursor back to
                // the actual character.
                const prev_cell = screen.cursorCellLeft(1);
                break :cell .{ prev_cell.wide == .wide, screen.cursor.x - 1 };
            };

            const alpha: u8 = if (!self.focused) 255 else alpha: {
                const alpha = 255 * self.config.cursor_opacity;
                break :alpha @intFromFloat(@ceil(alpha));
            };

            const render = switch (cursor_style) {
                .block,
                .block_hollow,
                .bar,
                .underline,
                => render: {
                    const sprite: font.Sprite = switch (cursor_style) {
                        .block => .cursor_rect,
                        .block_hollow => .cursor_hollow_rect,
                        .bar => .cursor_bar,
                        .underline => .underline,
                        .lock => unreachable,
                    };

                    break :render self.font_grid.renderGlyph(
                        self.alloc,
                        font.sprite_index,
                        @intFromEnum(sprite),
                        .{
                            .cell_width = if (wide) 2 else 1,
                            .grid_metrics = self.grid_metrics,
                        },
                    ) catch |err| {
                        log.warn("error rendering cursor glyph err={}", .{err});
                        return;
                    };
                },

                .lock => self.font_grid.renderCodepoint(
                    self.alloc,
                    0xF023, // lock symbol
                    .regular,
                    .text,
                    .{
                        .cell_width = if (wide) 2 else 1,
                        .grid_metrics = self.grid_metrics,
                    },
                ) catch |err| {
                    log.warn("error rendering cursor glyph err={}", .{err});
                    return;
                } orelse {
                    // This should never happen because we embed nerd
                    // fonts so we just log and return instead of fallback.
                    log.warn("failed to find lock symbol for cursor codepoint=0xF023", .{});
                    return;
                },
            };

            self.cells.setCursor(.{
                .mode = .cursor,
                .grid_pos = .{ x, screen.cursor.y },
                .color = .{ cursor_color.r, cursor_color.g, cursor_color.b, alpha },
                .glyph_pos = .{ render.glyph.atlas_x, render.glyph.atlas_y },
                .glyph_size = .{ render.glyph.width, render.glyph.height },
                .bearings = .{
                    @intCast(render.glyph.offset_x),
                    @intCast(render.glyph.offset_y),
                },
            });
        }

        fn addPreeditCell(
            self: *Self,
            cp: renderer.State.Preedit.Codepoint,
            coord: terminal.Coordinate,
        ) !void {
            // Preedit is rendered inverted
            const bg = self.foreground_color orelse self.default_foreground_color;
            const fg = self.background_color orelse self.default_background_color;

            // Render the glyph for our preedit text
            const render_ = self.font_grid.renderCodepoint(
                self.alloc,
                @intCast(cp.codepoint),
                .regular,
                .text,
                .{ .grid_metrics = self.grid_metrics },
            ) catch |err| {
                log.warn("error rendering preedit glyph err={}", .{err});
                return;
            };
            const render = render_ orelse {
                log.warn("failed to find font for preedit codepoint={X}", .{cp.codepoint});
                return;
            };

            // Add our opaque background cell
            self.cells.bgCell(coord.y, coord.x).* = .{
                bg.r, bg.g, bg.b, 255,
            };
            if (cp.wide and coord.x < self.cells.size.columns - 1) {
                self.cells.bgCell(coord.y, coord.x + 1).* = .{
                    bg.r, bg.g, bg.b, 255,
                };
            }

            // Add our text
            try self.cells.add(self.alloc, .text, .{
                .mode = .fg,
                .grid_pos = .{ @intCast(coord.x), @intCast(coord.y) },
                .color = .{ fg.r, fg.g, fg.b, 255 },
                .glyph_pos = .{ render.glyph.atlas_x, render.glyph.atlas_y },
                .glyph_size = .{ render.glyph.width, render.glyph.height },
                .bearings = .{
                    @intCast(render.glyph.offset_x),
                    @intCast(render.glyph.offset_y),
                },
            });
        }

        /// Sync the atlas data to the given texture. This copies the bytes
        /// associated with the atlas to the given texture. If the atlas no
        /// longer fits into the texture, the texture will be resized.
        fn syncAtlasTexture(
            self: *const Self,
            atlas: *const font.Atlas,
            texture: *Texture,
        ) !void {
            if (atlas.size > texture.width) {
                // Free our old texture
                texture.*.deinit();

                // Reallocate
                texture.* = try self.api.initAtlasTexture(atlas);
            }

            try texture.replaceRegion(0, 0, atlas.size, atlas.size, atlas.data);
        }
    };
}