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Comment on L.A. Rush blending problem

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Henrik Rydgård committed 2025-04-09 11:58:31 +02:00
1 parent f168aa3aee
commit 50410d0de3
1 file changed
+19 -2
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GPU/Common/GPUStateUtils.cpp
+19 -2
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@@ -420,8 +420,19 @@ ReplaceBlendType ReplaceBlendWithShader(GEBufferFormat bufferFormat) {
default:
switch (funcB) {
case GE_DSTBLEND_DOUBLESRCALPHA:
// Can't safely double alpha, will clamp.
{
// L.A. Rush ends up here (detail textures at the end of the frame). It uses FIXA = 0 (no src color contribution)
// but I still can't find a way to replicate the formula.
// If our framebuffer was floating point we could make it work (since that turns off clamping before blending)
// by just doubling src_alpha in the shader.
//
// It might be possible to replicate it if we implement a 2-pass decomposition:
// * First pass just does:
// src=ZERO dst=SRC_ALPHA.
// * Second pass renders with white input color. To double the resulting destination color:
// src=DST_COLOR dst=ONE
return REPLACE_BLEND_READ_FRAMEBUFFER;
}
case GE_DSTBLEND_DOUBLEINVSRCALPHA:
// Doubling alpha is safe for the inverse, will clamp to zero either way.
@@ -430,6 +441,7 @@ ReplaceBlendType ReplaceBlendWithShader(GEBufferFormat bufferFormat) {
case GE_DSTBLEND_DOUBLEDSTALPHA:
case GE_DSTBLEND_DOUBLEINVDSTALPHA:
if (bufferFormat == GE_FORMAT_565) {
// Alpha is irrelevant with this format.
return REPLACE_BLEND_STANDARD;
}
return REPLACE_BLEND_READ_FRAMEBUFFER;
@@ -437,9 +449,10 @@ ReplaceBlendType ReplaceBlendWithShader(GEBufferFormat bufferFormat) {
case GE_DSTBLEND_FIXB:
default:
if (gstate.getFixA() == 0xFFFFFF && gstate.getFixB() == 0x000000) {
// Some games specify this. Some cards may prefer blending off entirely.
// Some games specify this. Some GPUs may prefer blending off entirely.
return REPLACE_BLEND_NO;
} else if (gstate.getFixA() == 0xFFFFFF || gstate.getFixA() == 0x000000 || gstate.getFixB() == 0xFFFFFF || gstate.getFixB() == 0x000000) {
// We can represent this with standard factors.
return REPLACE_BLEND_STANDARD;
} else {
// Multiply the src color in the shader, that way it's always accurate.
@@ -467,6 +480,8 @@ ReplaceBlendType ReplaceBlendWithShader(GEBufferFormat bufferFormat) {
// Can't safely double alpha, will clamp. However, a copy may easily be worse due to overlap.
if (gstate_c.Use(GPU_USE_FRAMEBUFFER_FETCH))
return REPLACE_BLEND_READ_FRAMEBUFFER;
// Hm, this is similar to the L.A. Rush case above. This will not be accurate.
// Wonder in which games we encounter this?
return REPLACE_BLEND_PRE_SRC_2X_ALPHA;
} else {
// This means dst alpha/color is used in the src factor.
@@ -474,6 +489,8 @@ ReplaceBlendType ReplaceBlendWithShader(GEBufferFormat bufferFormat) {
// We will just hope that doubling alpha for the dst factor will not clamp too badly.
if (gstate_c.Use(GPU_USE_FRAMEBUFFER_FETCH))
return REPLACE_BLEND_READ_FRAMEBUFFER;
// Hm, this is similar to the L.A. Rush case above. This will not be accurate.
// Wonder in which games we encounter this?
return REPLACE_BLEND_2X_ALPHA;
}