Start work on porting cell shader

kitty/shaders/cell.slang

@@ -0,0 +1,104 @@
+#language slang 2026
+// Copyright (C) 2026 Kovid Goyal <kovid at kovidgoyal.net>
+// Distributed under terms of the GPLv3 license.
+
+// https://github.com/shader-slang/slang/issues/11874
+// warnings-disable: 41012
+
+#define NUM_COLORS 256
+
+extern static const bool DO_FG_OVERRIDE;
+extern static const uint FG_OVERRIDE_ALGO;
+extern static const float FG_OVERRIDE_THRESHOLD;
+extern static const bool TEXT_NEW_GAMMA;
+extern static const bool ONLY_FOREGROUND;
+extern static const bool ONLY_BACKGROUND;
+
+// Inputs {{{
+struct CellRenderDataStruct
+{
+    float use_cell_bg_for_selection_fg, use_cell_fg_for_selection_fg, use_cell_for_selection_bg;
+
+    uint default_fg, highlight_fg, highlight_bg, main_cursor_fg, main_cursor_bg, url_color, url_style, inverted, extra_cursor_fg, extra_cursor_bg;
+
+    uint columns, lines, sprites_xnum, sprites_ynum, cursor_shape, cell_width, cell_height;
+    uint cursor_x1, cursor_x2, cursor_y1, cursor_y2;
+    float cursor_opacity, inactive_text_alpha, dim_opacity, blink_opacity;
+
+    // must have unique entries with 0 being default_bg and unset being UINT32_MAX
+    uint bg_colors0, bg_colors1, bg_colors2, bg_colors3, bg_colors4, bg_colors5, bg_colors6, bg_colors7;
+    float bg_opacities0, bg_opacities1, bg_opacities2, bg_opacities3, bg_opacities4, bg_opacities5, bg_opacities6, bg_opacities7;
+};
+
+// Uniform Blocks (adjust binding slots as needed for your pipeline layout)
+ConstantBuffer<CellRenderDataStruct> CellRenderData;
+
+struct ColorTableStruct
+{
+    uint color_table[NUM_COLORS + MARK_MASK + MARK_MASK + 2];
+};
+
+ConstantBuffer<ColorTableStruct> ColorTable;
+
+uniform float gamma_lut[256];
+uniform Sampler2D<uint4> sprite_decorations_map;
+//
+
+static const int fg_index_map[3] = {0, 1, 0};
+static const uint2 cell_pos_map[4] = {
+    uint2(1u, 0u),  // right, top
+    uint2(1u, 1u),  // right, bottom
+    uint2(0u, 1u),  // left, bottom
+    uint2(0u, 0u)   // left, top
+};
+static const uint cursor_shape_map[] = {  // maps cursor shape to foreground sprite index
+   0u,  // NO_CURSOR
+   0u,  // BLOCK  (this is rendered as background)
+   2u,  // BEAM
+   3u,  // UNDERLINE
+   4u   // UNFOCUSED
+};
+
+// Vertex Input Attributes with explicit fixed locations
+struct VertexInput
+{
+    [[vk::location(0)]] uint3 colors       : COLORS;
+    [[vk::location(1)]] uint2 sprite_idx   : SPRITE_IDX;
+    [[vk::location(2)]] uint  is_selected  : IS_SELECTED;
+};
+
+struct VSOutput {
+    float4 position : SV_Position;
+
+    float3 background;
+    float4 effective_background_premul;
+    float  effective_text_alpha;
+    float3 sprite_pos;
+    float3 underline_pos;
+    float3 cursor_pos;
+    float3 strike_pos;
+    nointerpolation uint underline_exclusion_pos;
+    float3 cell_foreground;
+    float4 cursor_color_premult;
+    float3 decoration_fg;
+    float  colored_sprite;
+};
+
+
+[shader("vertex")]
+VSOutput vertex_main(
+    VertexInput vi,
+    uint vertex_id : SV_VertexID,
+    uniform uint draw_bg_bitfield,
+    uniform float row_offset,
+) {
+    int width, height;
+    sprite_decorations_map.GetDimensions(width, height);
+    uint4 data = sprite_decorations_map.Load(int3(1,2,0));
+    VSOutput r;
+    r.position = float4(vertex_id + draw_bg_bitfield, data[0] / width * height, row_offset, CellRenderData.cursor_opacity);
+    r.background = float3(ColorTable.color_table[vertex_id], vi.is_selected, 2);
+    return r;
+}
+
+

kitty/shaders/slang.py

@@ -62,6 +62,7 @@ def is_dir_slangc_version_ok(path: str) -> bool:
 
 def ensure_cache_dir(path: str) -> None:
     os.makedirs(path, exist_ok=True)
+    # slang IR is version dependent and the compiler often crashes when loading .slang-module from another version
     if not is_dir_slangc_version_ok(path):
         shutil.rmtree(path)
         os.makedirs(path, exist_ok=True)