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Read the CLUT8 depal byte of an 8888 framebuffer exactly

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int(t * 254.99) gave each byte value minus one: c / 255 * 254.99 lands just
below c. With 255.99 it's c for every byte. The texel also gets the best
available precision: in fp16 the product rounds, and 16 of the 256 bytes
came out one low. Burnout Dominator's car select lens flare gets closer to the
PSP on Vulkan (57 -> 48 px); nothing else in the frame dump set changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Henrik RydgårdandClaude Opus 5.5 committed 2026-10-10 01:04:23 +02:00
1 parent a404f2ae7c
commit 70bc01925e
1 file changed
+6 -5
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GPU/Common/FragmentShaderGenerator.cpp
+6 -5
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@@ -829,15 +829,16 @@ bool GenerateFragmentShader(const FShaderID &id, char *buffer, const ShaderLangu
p.C(" uv_round.x = floor(uv_round.x * 0.5);\n");
}
p.C(" uv_round = (uv_round + 0.5) / tsize;\n");
p.C(" vec4 t = ").SampleTexture2D("tex", "uv_round").C(";\n");
// The byte decodes below are exact in fp32, but the product rounding in fp16 makes 16 of 256 bytes come out one low.
p.F(" %s vec4 t = ", prec).SampleTexture2D("tex", "uv_round").C(";\n");
p.C(" int index;\n");
switch (shaderDepalFmt) {
case GE_FORMAT_8888:
p.C(" switch (component) {\n");
p.C(" case 0: index = int(t.x * 254.99); break;\n"); // TODO: Not sure why 254.99 instead of 255.99, but it's currently needed.
p.C(" case 1: index = int(t.y * 254.99); break;\n");
p.C(" case 2: index = int(t.z * 254.99); break;\n");
p.C(" case 3: index = int(t.w * 254.99); break;\n");
p.C(" case 0: index = int(t.x * 255.99); break;\n");
p.C(" case 1: index = int(t.y * 255.99); break;\n");
p.C(" case 2: index = int(t.z * 255.99); break;\n");
p.C(" case 3: index = int(t.w * 255.99); break;\n");
p.C(" }\n");
break;
default: