blob: a24577a09ad42a5293fe990cddd6824651fa25e2 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
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;
}
|