More work on slangc compilation

kitty/shaders/alpha-blend.slang

@@ -0,0 +1,28 @@
+#language slang 2026
+// Copyright (C) 2026 Kovid Goyal <kovid at kovidgoyal.net>
+// Distributed under terms of the GPLv3 license.
+
+module alpha_blend;
+
+// Alpha blend two colors returning the resulting color pre-multiplied by its alpha
+// and its alpha. See https://en.wikipedia.org/wiki/Alpha_compositing
+public float4 alpha_blend(float4 over, float4 under) {
+    float alpha = lerp(under.a, 1.0f, over.a);
+    float3 combined_color = lerp(under.rgb * under.a, over.rgb, over.a);
+    return float4(combined_color, alpha);
+}
+
+// Same as alpha_blend() except that it assumes over and under are both premultiplied.
+public float4 alpha_blend_premul(float4 over, float4 under) {
+    float inv_over_alpha = 1.0f - over.a;
+    float alpha = over.a + under.a * inv_over_alpha;
+    return float4(over.rgb + under.rgb * inv_over_alpha, alpha);
+}
+
+// Same as alpha_blend_premul with under_alpha = 1 outputs a blended color
+// with alpha 1 which is effectively pre-multiplied since alpha is 1
+public float4 alpha_blend_premul(float4 over, float3 under) {
+    float inv_over_alpha = 1.0f - over.a;
+    return float4(over.rgb + under.rgb * inv_over_alpha, 1.0f);
+}
+

kitty/shaders/graphics.slang

@@ -13,7 +13,7 @@ struct VSOutput
 
 
 [shader("vertex")]
-VSOutput main(
+VSOutput vertex_main(
     uint vertex_id : SV_VertexID,
     uniform float4 src_rect,
     uniform float4 dest_rect,
@@ -25,3 +25,11 @@ VSOutput main(
     return output;
 }
 
+Sampler2D image;
+
+[shader("fragment")]
+float4 fragment_main(float2 texcoord : TEXCOORD) : SV_Target
+{
+    float4 color = image.Sample(texcoord);
+    return color;
+}

kitty/shaders/slang.py

@@ -178,7 +178,7 @@ def iter_entry_point_shaders(sources: dict[str, SlangFile], build_dir: str, dest
 def commands_to_compile_to_spirv(sources: dict[str, SlangFile], build_dir: str, dest_dir: str, built_files: list[str]) -> Iterator[Command]:
     for base_dest, slang_module, cmd, sfile in iter_entry_point_shaders(sources, build_dir, dest_dir):
         dest = f'{base_dest}.spv'
-        cmd += ['-target', 'spirv', '-o', dest]
+        cmd += ['-target', 'spirv', '-capability', 'vk_mem_model', '-fvk-use-entrypoint-name', '-o', dest]
         output_mtime = safe_mtime(dest)
         module_mtime = os.path.getmtime(slang_module)
         needs_build = output_mtime < module_mtime
@@ -189,19 +189,17 @@ def commands_to_compile_to_spirv(sources: dict[str, SlangFile], build_dir: str,
 
 def commands_to_compile_to_glsl(sources: dict[str, SlangFile], build_dir: str, dest_dir: str, built_glsl_files: list[str]) -> Iterator[Command]:
     for base_dest, slang_module, cmd, sfile in iter_entry_point_shaders(sources, build_dir, dest_dir):
-        output_mtime = future()
-        dest_files = []
-        cmd.extend(('-line-directive-mode', 'none'))
-        for ep in sfile.entry_points:
-            dest = f'{base_dest}.{ep.stage.name}.glsl'
-            cmd += ['-entry', ep.name, '-stage', ep.stage.name, '-target', 'glsl', '-profile', 'glsl_330', '-o', dest]
-            dest_files.append(dest)
-            output_mtime = min(output_mtime, safe_mtime(dest))
         module_mtime = os.path.getmtime(slang_module)
-        needs_build = output_mtime < module_mtime
-        if needs_build:
-            built_glsl_files.extend(dest_files)
-        yield Command(needs_build, f'Linking |{os.path.basename(slang_module)}| to GLSL ...', cmd)
+        for ep in sfile.entry_points:
+            c = list(cmd)
+            c.extend(('-line-directive-mode', 'none', '-target', 'glsl', '-profile', 'glsl_330'))
+            dest = f'{base_dest}.{ep.stage.name}.glsl'
+            c += ['-entry', ep.name, '-stage', ep.stage.name, '-o', dest]
+            output_mtime = safe_mtime(dest)
+            needs_build = output_mtime < module_mtime
+            if needs_build:
+                built_glsl_files.append(dest)
+            yield Command(needs_build, f'Linking |{os.path.basename(slang_module)}| to GLSL {ep.stage} shader ...', c)
 
 
 def fixup_opengl_code(glsl_code: str) -> str:
@@ -234,7 +232,7 @@ def fixup_opengl_code(glsl_code: str) -> str:
                 line = '#version 330 core'
             elif line.startswith('#extension ') or line in ('layout(row_major) buffer;', 'layout(push_constant)'):
                 line = '// ' + line
-            elif line.startswith('layout(location ='):
+            elif line.startswith('layout(location =') or line.startswith('layout(binding ='):
                 line = '// ' + line
             else:
                 words = line.split()

kitty/shaders/utils.slang

@@ -0,0 +1,34 @@
+#language slang 2026
+// Copyright (C) 2026 Kovid Goyal <kovid at kovidgoyal.net>
+// Distributed under terms of the GPLv3 license.
+
+module utils;
+
+// Return 0 if x < 1 otherwise 1
+__generic<T : __BuiltinFloatingPointType, int N = 1>
+vector<T, N> zero_or_one(vector<T, N> x) {
+    return step((vector<T, N>)1.0f, x);
+}
+
+// condition must be zero or one. When 1 thenval is returned otherwise elseval
+__generic<T : __BuiltinFloatingPointType, int N = 1>
+vector<T, N> if_one_then(vector<T, N> condition, vector<T, N> thenval, vector<T, N> elseval) {
+    return lerp(elseval, thenval, condition);
+}
+
+// a < b ? thenval : elseval
+__generic<T : __BuiltinFloatingPointType, int N = 1>
+vector<T, N> if_less_than(vector<T, N> a, vector<T, N> b, vector<T, N> thenval, vector<T, N> elseval) {
+    return lerp(thenval, elseval, step(b, a));
+}
+
+// Replaces vec4(rgb * a, a)
+float4 vec4_premul(float3 rgb, float a) {
+    return float4(rgb * a, a);
+}
+
+// Overloaded variation replacing vec4(rgba.rgb * rgba.a, rgba.a)
+float4 vec4_premul(float4 rgba) {
+    return float4(rgba.rgb * rgba.a, rgba.a);
+}
+