1 files changed, 36 insertions, 0 deletions
diff --git a/gfx/layers/d3d11/mlgshaders/blend-ps-generated.hlslh.tpl b/gfx/layers/d3d11/mlgshaders/blend-ps-generated.hlslh.tpl
new file mode 100644
index 0000000000..a24577a09a
--- /dev/null
+++ b/gfx/layers/d3d11/mlgshaders/blend-ps-generated.hlslh.tpl
@@ -0,0 +1,36 @@
+float4 Blend{BLEND_FUNC}PS(const VS_BLEND_OUTPUT aInput) : SV_Target
+{
+  if (!RectContainsPoint(aInput.vClipRect, aInput.vPosition.xy)) {
+    discard;
+  }
+
+  float4 backdrop = tBackdrop.Sample(sSampler, aInput.vBackdropCoords);
+  float4 source = simpleTex.Sample(sSampler, aInput.vTexCoords);
+
+  // Apply masks to the source texture, not the result.
+  source *= ReadMask(aInput.vMaskCoords);
+
+  // Shortcut when the backdrop or source alpha is 0, otherwise we may leak
+  // infinity into the blend function and return incorrect results.
+  if (backdrop.a == 0.0) {
+    return source;
+  }
+  if (source.a == 0.0) {
+    return float4(0, 0, 0, 0);
+  }
+
+  // The spec assumes there is no premultiplied alpha. The backdrop and
+  // source are both render targets and always premultiplied, so we undo
+  // that here.
+  backdrop.rgb /= backdrop.a;
+  source.rgb /= source.a;
+
+  float4 result;
+  result.rgb = Blend{BLEND_FUNC}(backdrop.rgb, source.rgb);
+  result.a = source.a;
+
+  // Factor backdrop alpha, then premultiply for the final OP_OVER.
+  result.rgb = (1.0 - backdrop.a) * source.rgb + backdrop.a * result.rgb;
+  result.rgb *= result.a;
+  return result;
+}