Port the blit shader

kitty/shaders/blit.slang

@@ -0,0 +1,32 @@
+#language slang 2026
+// Copyright (C) 2026 Kovid Goyal <kovid at kovidgoyal.net>
+// Distributed under terms of the GPLv3 license.
+
+import blit_common;
+import alpha_blend;
+import utils;
+import linear2srgb;
+
+struct VSOutput {
+    float2 texcoord : TEXCOORD;
+    float4 position : SV_Position;
+};
+
+
+[shader("vertex")]
+VSOutput vertex_main(
+    uint vertex_id : SV_VertexID,
+    uniform float4 src_rect,
+    uniform float4 dest_rect,
+) {
+    BlitOutput ans = get_coords_for_blit(vertex_id, src_rect, dest_rect);
+    return {ans.texcoord, float4(ans.position[0], ans.position[1], 0.0, 1.0)};
+}
+
+uniform Sampler2D image;
+
+[shader("fragment")]
+float4 fragment_main(float2 texcoord : TEXCOORD) : SV_Target {
+    float4 color_premul = image.Sample(texcoord);
+    return vec4_premul(linear2srgb(color_premul.rgb / color_premul.a), color_premul.a);
+}

kitty/shaders/graphics.slang

@@ -24,10 +24,7 @@ VSOutput vertex_main(
     uniform float4 dest_rect,
 ) {
     BlitOutput ans = get_coords_for_blit(vertex_id, src_rect, dest_rect);
-    VSOutput output;
-    output.texcoord = ans.texcoord;
-    output.position = float4(ans.position[0], ans.position[1], 0.0, 1.0);
-    return output;
+    return {ans.texcoord, float4(ans.position[0], ans.position[1], 0.0, 1.0)};
 }
 
 uniform Sampler2D image;

kitty/shaders/linear2srgb.slang

@@ -0,0 +1,38 @@
+#language slang 2026
+// Copyright (C) 2026 Kovid Goyal <kovid at kovidgoyal.net>
+// Distributed under terms of the GPLv3 license.
+
+module linear2srgb;
+
+// Scalar sRGB to Linear conversion
+public float srgb2linear(float x) {
+    float lower = x / 12.92;
+    float upper = pow((x + 0.055f) / 1.055f, 2.4f);
+
+    // GLSL mix() is replaced by Slang's lerp()
+    return lerp(lower, upper, step(0.04045f, x));
+}
+
+// Scalar Linear to sRGB conversion
+public float linear2srgb(float x) {
+    float lower = 12.92 * x;
+    float upper = 1.055 * pow(x, 1.0f / 2.4f) - 0.055f;
+
+    return lerp(lower, upper, step(0.0031308f, x));
+}
+
+// Vector Linear to sRGB conversion
+public float3 linear2srgb(float3 x) {
+    float3 lower = 12.92 * x;
+    float3 upper = 1.055 * pow(x, float3(1.0f / 2.4f)) - 0.055f;
+
+    return lerp(lower, upper, step(float3(0.0031308f), x));
+}
+
+// Vector sRGB to Linear conversion
+public float3 srgb2linear(float3 c) {
+    // You can call the scalar version per-component,
+    // or pass the whole vector if you overload it for float3.
+    return float3(srgb2linear(c.r), srgb2linear(c.g), srgb2linear(c.b));
+}
+