Add support for customizing background image offset

src/config.zig

@@ -34,6 +34,7 @@ pub const Path = Config.Path;
 pub const ShellIntegrationFeatures = Config.ShellIntegrationFeatures;
 pub const WindowPaddingColor = Config.WindowPaddingColor;
 pub const BackgroundImageMode = Config.BackgroundImageMode;
+pub const BackgroundImagePosition = Config.BackgroundImagePosition;
 
 // Alternate APIs
 pub const CAPI = @import("config/CAPI.zig");

src/config/Config.zig

@@ -474,18 +474,25 @@ foreground: Color = .{ .r = 0xFF, .g = 0xFF, .b = 0xFF },
 ///   * `cover` - Image is centered in the window, preserving the aspect ratio
 ///     but cropping the image to fill the window, as needed.
 ///   * `tiled` - Image is repeated horizontally and vertically to fill the window.
-///   * `centered` - Image is centered in the window and displayed 1-to-1 pixel
-///     scale, preserving both the aspect ratio and the image size.
-///   * `top-left` - Image is anchored to the top left corner of the window,
-///     preserving the aspect ratio.
-///   * `top-right` - Image is anchored to the top right corner of the window,
-///     preserving the aspect ratio.
-///   * `bottom-left` - Image is anchored to the bottom left corner of the window,
-///     preserving the aspect ratio.
-///   * `bottom-right` - Image is anchored to the bottom right corner of the window,
-///     preserving the aspect ratio.
+///   * `none` - Image is displayed 1-to-1 pixel scale, preserving both the aspect
+///     ratio and the image size.
 ///
-@"background-image-mode": BackgroundImageMode = .contain,
+@"background-image-mode": BackgroundImageMode = .none,
+
+/// Background image position.
+///
+/// Valid values are:
+///   * `top-left`
+///   * `top-center`
+///   * `top-right`
+///   * `center-left`
+///   * `center`
+///   * `center-right`
+///   * `bottom-left`
+///   * `bottom-center`
+///   * `bottom-right`
+///
+@"background-image-position": BackgroundImagePosition = .center,
 
 /// The foreground and background color for selection. If this is not set, then
 /// the selection color is just the inverted window background and foreground
@@ -6197,10 +6204,24 @@ pub const BackgroundImageMode = enum(u8) {
     fill = 1,
     cover = 2,
     tiled = 3,
-    centered = 4,
-    @"top-left" = 5,
-    @"top-right" = 6,
-    @"bottom-left" = 7,
+    none = 4,
+};
+
+/// See background-image-position
+///
+/// This enum is used to set the background image position. The shader expects
+/// a `uint`, so we use `u8` here. The values for each position should be kept
+/// in sync with the values in the vertex shader used to render the
+/// background image (`bgimage`).
+pub const BackgroundImagePosition = enum(u8) {
+    @"top-left" = 0,
+    @"top-center" = 1,
+    @"top-right" = 2,
+    @"center-left" = 3,
+    center = 4,
+    @"center-right" = 5,
+    @"bottom-left" = 6,
+    @"bottom-center" = 7,
     @"bottom-right" = 8,
 };
 

src/renderer/OpenGL.zig

@@ -149,6 +149,9 @@ background_image_opacity: f32,
 /// The background image mode to use.
 background_image_mode: configpkg.BackgroundImageMode,
 
+/// The background image position to use.
+background_image_position: configpkg.BackgroundImagePosition,
+
 /// The current background image to draw. If it is null, then we will not
 /// draw any background image.
 current_background_image: ?Image = null,
@@ -302,6 +305,7 @@ pub const DerivedConfig = struct {
     background_image: ?configpkg.Path,
     background_image_opacity: f32,
     background_image_mode: configpkg.BackgroundImageMode,
+    background_image_position: configpkg.BackgroundImagePosition,
     foreground: terminal.color.RGB,
     selection_background: ?terminal.color.RGB,
     selection_foreground: ?terminal.color.RGB,
@@ -370,6 +374,7 @@ pub const DerivedConfig = struct {
             .background_image = background_image,
             .background_image_opacity = config.@"background-image-opacity",
             .background_image_mode = config.@"background-image-mode",
+            .background_image_position = config.@"background-image-position",
 
             .invert_selection_fg_bg = config.@"selection-invert-fg-bg",
             .bold_is_bright = config.@"bold-is-bright",
@@ -438,6 +443,7 @@ pub fn init(alloc: Allocator, options: renderer.Options) !OpenGL {
         .background_image = options.config.background_image,
         .background_image_opacity = options.config.background_image_opacity,
         .background_image_mode = options.config.background_image_mode,
+        .background_image_position = options.config.background_image_position,
         .cursor_invert = options.config.cursor_invert,
         .surface_mailbox = options.surface_mailbox,
         .deferred_font_size = .{ .metrics = grid.metrics },
@@ -2288,6 +2294,7 @@ pub fn changeConfig(self: *OpenGL, config: *DerivedConfig) !void {
     self.background_image = config.background_image;
     self.background_image_opacity = config.background_image_opacity;
     self.background_image_mode = config.background_image_mode;
+    self.background_image_position = config.background_image_position;
     if (self.current_background_image) |*img| {
         img.markForUnload();
     }
@@ -2635,6 +2642,7 @@ fn drawBackgroundImage(
         .terminal_width = self.size.terminal().width,
         .terminal_height = self.size.terminal().height,
         .mode = self.background_image_mode,
+        .position_index = self.background_image_position,
     }, .static_draw);
     try gl_state.bgimage_program.program.setUniform("opacity", self.config.background_image_opacity);
 

src/renderer/opengl/BackgroundImageProgram.zig

@@ -12,6 +12,9 @@ pub const Input = extern struct {
 
     /// uint mode
     mode: configpkg.BackgroundImageMode = .contain,
+
+    /// uint position_index
+    position_index: configpkg.BackgroundImagePosition = .center,
 };
 
 program: gl.Program,
@@ -60,10 +63,14 @@ pub fn init() !BackgroundImageProgram {
     offset += 2 * @sizeOf(u32);
     try vbobind.attributeIAdvanced(1, 1, gl.c.GL_UNSIGNED_BYTE, @sizeOf(Input), offset);
     offset += 1 * @sizeOf(u8);
+    try vbobind.attributeIAdvanced(2, 1, gl.c.GL_UNSIGNED_BYTE, @sizeOf(Input), offset);
+    offset += 1 * @sizeOf(u8);
     try vbobind.enableAttribArray(0);
     try vbobind.enableAttribArray(1);
+    try vbobind.enableAttribArray(2);
     try vbobind.attributeDivisor(0, 1);
     try vbobind.attributeDivisor(1, 1);
+    try vbobind.attributeDivisor(2, 1);
 
     return .{
         .program = program,

src/renderer/shaders/bgimage.v.glsl

@@ -7,14 +7,11 @@ const uint MODE_CONTAIN = 0u;
 const uint MODE_FILL = 1u;
 const uint MODE_COVER = 2u;
 const uint MODE_TILED = 3u;
-const uint MODE_CENTERED = 4u;
-const uint MODE_TOP_LEFT = 5u;
-const uint MODE_TOP_RIGHT = 6u;
-const uint MODE_BOTTOM_LEFT = 7u;
-const uint MODE_BOTTOM_RIGHT = 8u;
+const uint MODE_NONE = 4u;
 
 layout (location = 0) in vec2 terminal_size;
 layout (location = 1) in uint mode;
+layout (location = 2) in uint position_index;
 
 out vec2 tex_coord;
 
@@ -58,12 +55,8 @@ void main() {
 			scale.y = aspect_ratio.x / aspect_ratio.y;
 		}
 		break;
-	case MODE_CENTERED:
-	case MODE_TOP_LEFT:
-	case MODE_TOP_RIGHT:
-	case MODE_BOTTOM_LEFT:
-	case MODE_BOTTOM_RIGHT:
-		// If centered, the final scale of the image should match the actual
+	case MODE_NONE:
+		// If none, the final scale of the image should match the actual
 		// size of the image and should be centered
 		scale.x = image_size.x / terminal_size.x;
 		scale.y = image_size.y / terminal_size.y;
@@ -76,27 +69,10 @@ void main() {
 
 	vec2 final_image_size = terminal_size * position * scale;
 	vec2 offset = vec2(0.0, 0.0);
-	switch (mode) {
-	case MODE_CONTAIN:
-	case MODE_FILL:
-	case MODE_COVER:
-	case MODE_TILED:
-	case MODE_CENTERED:
-		offset = (terminal_size * (1.0 - scale)) / 2.0;
-		break;
-	case MODE_TOP_LEFT:
-		offset = vec2(0.0, 0.0);
-		break;
-	case MODE_TOP_RIGHT:
-		offset = vec2(terminal_size.x - image_size.x, 0.0);
-		break;
-	case MODE_BOTTOM_LEFT:
-		offset = vec2(0.0, terminal_size.y - image_size.y);
-		break;
-	case MODE_BOTTOM_RIGHT:
-		offset = vec2(terminal_size.x - image_size.x, terminal_size.y - image_size.y);
-		break;
-	}
+
+	uint y_pos = position_index / 3u; // 0 = top, 1 = center, 2 = bottom
+	uint x_pos = position_index % 3u; // 0 = left, 1 = center, 2 = right
+	offset = ((terminal_size * (1.0 - scale)) / 2.0) * vec2(x_pos, y_pos);
 	gl_Position = projection * vec4(final_image_size.xy + offset, 0.0, 1.0);
 	tex_coord = position;
 	if (mode == MODE_TILED) {