postfx subpixel

source/core/rendering/sdl3gpu/sdl3gpu_shader.cpp

@@ -61,7 +61,12 @@ fragment float4 postfx_fs(PostVOut                 in    [[stage_in]],
     color.b = scene.sample(samp, in.uv - float2( ca, 0.0)).b;
     color.a = scene.sample(samp, in.uv).a;
 
-    float scan = 0.85 + 0.15 * sin(in.uv.y * 3.14159265 * u.screen_height);
+    float texHeight  = float(scene.get_height());
+    float scaleY     = u.screen_height / texHeight;
+    float screenY    = in.uv.y * u.screen_height;
+    float posInRow   = fmod(screenY, scaleY);
+    float scanLineDY = posInRow / scaleY - 0.5;
+    float scan       = max(1.0 - scanLineDY * scanLineDY * 6.0, 0.12) * 3.5;
     color.rgb *= mix(1.0, scan, u.scanline_strength);
 
     float2 d = in.uv - float2(0.5, 0.5);
@@ -312,6 +317,8 @@ void SDL3GPUShader::render() {
         return;
     }
 
+    uniforms_.screen_height = static_cast<float>(sh);
+
     // ---- Render pass: PostFX → swapchain ----
     SDL_GPUColorTargetInfo color_target = {};
     color_target.texture = swapchain;