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37 lines
1.1 KiB
Smarty
37 lines
1.1 KiB
Smarty
float4 Blend{BLEND_FUNC}PS(const VS_BLEND_OUTPUT aInput) : SV_Target
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{
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if (!RectContainsPoint(aInput.vClipRect, aInput.vPosition.xy)) {
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discard;
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}
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float4 backdrop = tBackdrop.Sample(sSampler, aInput.vBackdropCoords);
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float4 source = simpleTex.Sample(sSampler, aInput.vTexCoords);
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// Apply masks to the source texture, not the result.
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source *= ReadMask(aInput.vMaskCoords);
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// Shortcut when the backdrop or source alpha is 0, otherwise we may leak
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// infinity into the blend function and return incorrect results.
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if (backdrop.a == 0.0) {
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return source;
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}
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if (source.a == 0.0) {
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return float4(0, 0, 0, 0);
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}
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// The spec assumes there is no premultiplied alpha. The backdrop and
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// source are both render targets and always premultiplied, so we undo
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// that here.
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backdrop.rgb /= backdrop.a;
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source.rgb /= source.a;
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float4 result;
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result.rgb = Blend{BLEND_FUNC}(backdrop.rgb, source.rgb);
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result.a = source.a;
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// Factor backdrop alpha, then premultiply for the final OP_OVER.
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result.rgb = (1.0 - backdrop.a) * source.rgb + backdrop.a * result.rgb;
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result.rgb *= result.a;
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return result;
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}
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