renderer/metal: load custom shaders

src/config/Config.zig

@@ -599,6 +599,29 @@ keybind: Keybinds = .{},
 /// need KAM, you don't need it.
 @"vt-kam-allowed": bool = false,
 
+/// Custom shaders to run after the default shaders. This is a file path
+/// to a GLSL-syntax shader for all platforms.
+///
+/// WARNING: Invalid shaders can cause Ghostty to become unusable such as by
+/// causing the window to be completely black. If this happens, you can
+/// unset this configuration to disable the shader.
+///
+/// The shader API is identical to the ShaderToy API: you specify a `mainImage`
+/// function and the available uniforms match ShaderToy. The iChannel0 uniform
+/// is a texture containing the rendered terminal screen.
+///
+/// If the shader fails to compile, the shader will be ignored. Any errors
+/// related to shader compilation will not show up as configuration errors
+/// and only show up in the log, since shader compilation happens after
+/// configuration loading on the dedicated render thread. If your shader is
+/// not working, another way to debug is to run the `ghostty
+/// +custom-shader-compile` command which will compile the shader and show any
+/// errors. For interactive development, use ShaderToy.com.
+///
+/// This can be repeated multiple times to load multiple shaders. The shaders
+/// will be run in the order they are specified.
+@"custom-shader": RepeatablePath = .{},
+
 /// If anything other than false, fullscreen mode on macOS will not use the
 /// native fullscreen, but make the window fullscreen without animations and
 /// using a new space. It's faster than the native fullscreen mode since it

src/main.zig

@@ -4,6 +4,7 @@ const Allocator = std.mem.Allocator;
 const build_config = @import("build_config.zig");
 const options = @import("build_options");
 const glfw = @import("glfw");
+const glslang = @import("glslang");
 const macos = @import("macos");
 const tracy = @import("tracy");
 const cli = @import("cli.zig");
@@ -267,6 +268,9 @@ pub const GlobalState = struct {
         // We need to make sure the process locale is set properly. Locale
         // affects a lot of behaviors in a shell.
         try internal_os.ensureLocale(self.alloc);
+
+        // Initialize glslang for shader compilation
+        try glslang.init();
     }
 
     /// Cleans up the global state. This doesn't _need_ to be called but

src/renderer/Metal.zig

@@ -10,6 +10,7 @@ const glfw = @import("glfw");
 const objc = @import("objc");
 const macos = @import("macos");
 const imgui = @import("imgui");
+const glslang = @import("glslang");
 const apprt = @import("../apprt.zig");
 const configpkg = @import("../config.zig");
 const font = @import("../font/main.zig");
@@ -17,8 +18,10 @@ const terminal = @import("../terminal/main.zig");
 const renderer = @import("../renderer.zig");
 const math = @import("../math.zig");
 const Surface = @import("../Surface.zig");
+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 mtl = @import("metal/api.zig");
@@ -116,8 +119,10 @@ texture_color: objc.Object, // MTLTexture
 /// 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_features: std.ArrayList([]const u8),
+    font_features: std.ArrayListUnmanaged([]const u8),
     font_styles: font.Group.StyleStatus,
     cursor_color: ?terminal.color.RGB,
     cursor_opacity: f64,
@@ -128,17 +133,21 @@ pub const DerivedConfig = struct {
     selection_background: ?terminal.color.RGB,
     selection_foreground: ?terminal.color.RGB,
     invert_selection_fg_bg: bool,
+    custom_shaders: std.ArrayListUnmanaged([]const u8),
 
     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".value.list.clone(alloc);
+
         // Copy our font features
-        var font_features = features: {
-            var clone = try config.@"font-feature".list.clone(alloc_gpa);
-            break :features clone.toManaged(alloc_gpa);
-        };
-        errdefer font_features.deinit();
+        const font_features = try config.@"font-feature".list.clone(alloc);
 
         // Get our font styles
         var font_styles = font.Group.StyleStatus.initFill(true);
@@ -177,11 +186,15 @@ pub const DerivedConfig = struct {
                 bg.toTerminalRGB()
             else
                 null,
+
+            .custom_shaders = custom_shaders,
+
+            .arena = arena,
         };
     }
 
     pub fn deinit(self: *DerivedConfig) void {
-        self.font_features.deinit();
+        self.arena.deinit();
     }
 };
 
@@ -203,6 +216,10 @@ pub fn surfaceInit(surface: *apprt.Surface) !void {
 }
 
 pub fn init(alloc: Allocator, options: renderer.Options) !Metal {
+    var arena = ArenaAllocator.init(alloc);
+    defer arena.deinit();
+    const arena_alloc = arena.allocator();
+
     // Initialize our metal stuff
     const device = objc.Object.fromId(mtl.MTLCreateSystemDefaultDevice());
     const queue = device.msgSend(objc.Object, objc.sel("newCommandQueue"), .{});
@@ -256,6 +273,17 @@ pub fn init(alloc: Allocator, options: renderer.Options) !Metal {
     });
     errdefer buf_instance.deinit();
 
+    // Load our custom shaders
+    const custom_shaders: []const [:0]const u8 = shadertoy.loadFromFiles(
+        arena_alloc,
+        options.config.custom_shaders.items,
+        .msl,
+    ) catch |err| err: {
+        log.warn("error loading custom shaders err={}", .{err});
+        break :err &.{};
+    };
+    _ = custom_shaders;
+
     // Initialize our shaders
     var shaders = try Shaders.init(alloc, device, &.{
         @embedFile("shaders/temp3.metal"),

src/renderer/shadertoy.zig

@@ -2,9 +2,81 @@ const std = @import("std");
 const builtin = @import("builtin");
 const assert = std.debug.assert;
 const Allocator = std.mem.Allocator;
+const ArenaAllocator = std.heap.ArenaAllocator;
 const glslang = @import("glslang");
 const spvcross = @import("spirv_cross");
 
+const log = std.log.scoped(.shadertoy);
+
+/// The target to load shaders for.
+pub const Target = enum { msl };
+
+/// Load a set of shaders from files and convert them to the target
+/// format. The shader order is preserved.
+pub fn loadFromFiles(
+    alloc_gpa: Allocator,
+    paths: []const []const u8,
+    target: Target,
+) ![]const [:0]const u8 {
+    var list = std.ArrayList([:0]const u8).init(alloc_gpa);
+    defer list.deinit();
+    errdefer for (list.items) |shader| alloc_gpa.free(shader);
+
+    for (paths) |path| {
+        const shader = try loadFromFile(alloc_gpa, path, target);
+        log.info("loaded custom shader path={s}", .{path});
+        try list.append(shader);
+    }
+
+    return try list.toOwnedSlice();
+}
+
+/// Load a single shader from a file and convert it to the target language
+/// ready to be used with renderers.
+pub fn loadFromFile(
+    alloc_gpa: Allocator,
+    path: []const u8,
+    target: Target,
+) ![:0]const u8 {
+    var arena = ArenaAllocator.init(alloc_gpa);
+    defer arena.deinit();
+    const alloc = arena.allocator();
+
+    // Load the shader fiel
+    const cwd = std.fs.cwd();
+    const file = try cwd.openFile(path, .{});
+    defer file.close();
+
+    // Read it all into memory -- we don't expect shaders to be large.
+    var buf_reader = std.io.bufferedReader(file.reader());
+    const src = try buf_reader.reader().readAllAlloc(
+        alloc,
+        4 * 1024 * 1024, // 4MB
+    );
+
+    // Convert to full GLSL
+    const glsl: [:0]const u8 = glsl: {
+        var list = std.ArrayList(u8).init(alloc);
+        try glslFromShader(list.writer(), src);
+        try list.append(0);
+        break :glsl list.items[0 .. list.items.len - 1 :0];
+    };
+
+    // Convert to SPIR-V
+    const spirv: []const u8 = spirv: {
+        var list = std.ArrayList(u8).init(alloc);
+        try spirvFromGlsl(list.writer(), null, glsl);
+        break :spirv list.items;
+    };
+
+    // Convert to MSL
+    return switch (target) {
+        // Important: using the alloc_gpa here on purpose because this
+        // is the final result that will be returned to the caller.
+        .msl => try mslFromSpv(alloc_gpa, spirv),
+    };
+}
+
 /// Convert a ShaderToy shader into valid GLSL.
 ///
 /// ShaderToy shaders aren't full shaders, they're just implementing a