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SoftGPU: Apply UV scale and offset like the GE

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In UV gen mode 0 the software renderer now decodes UVs without the prescale
and applies u * scale + offset itself: the product as a float24, then the
GE's guard-bit-less add. Bit exact on gpu/probe exp66 for float, 16-bit and
8-bit UVs (which are unsigned).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Henrik RydgårdandClaude Opus 5.5 committed 2026-10-02 15:09:42 -06:00
1 parent abd4c21b9b
commit 2d3c8fa0cb
2 files changed
+27 -5
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GPU/Software/TransformUnit.cpp
+23 -1
View File
@@ -428,13 +428,28 @@ struct TransformState {
uint8_t uvGenMode : 2;
uint8_t matrixMode : 2;
};
// The UV scale and offset, applied in ReadVertex with the GE's arithmetic (the vertex decoder leaves
// them out then, see UsesGEUVScale).
bool geUVScale;
float uvScale[2];
float uvOffset[2];
};
// UV gen mode 0 in transform mode: u * scale + offset as the GE computes it (gpu/probe exp66).
static bool UsesGEUVScale(u32 vertexType) {
return (vertexType & GE_VTYPE_THROUGH_MASK) == 0 && gstate.getUVGenMode() == GE_TEXMAP_TEXTURE_COORDS;
}
void ComputeTransformState(TransformState *state, const VertexReader &vreader) {
state->enableTransform = !vreader.isThrough();
state->enableLighting = gstate.isLightingEnabled();
state->enableFog = gstate.isFogEnabled();
state->readUV = !gstate.isModeClear() && gstate.isTextureMapEnabled() && vreader.hasUV();
state->geUVScale = !vreader.isThrough() && gstate.getUVGenMode() == GE_TEXMAP_TEXTURE_COORDS;
state->uvScale[0] = TruncateToFloat24(getFloat24(gstate.texscaleu));
state->uvScale[1] = TruncateToFloat24(getFloat24(gstate.texscalev));
state->uvOffset[0] = TruncateToFloat24(getFloat24(gstate.texoffsetu));
state->uvOffset[1] = TruncateToFloat24(getFloat24(gstate.texoffsetv));
state->negateNormals = gstate.areNormalsReversed();
state->uvGenMode = gstate.getUVGenMode();
@@ -549,6 +564,13 @@ ClipVertexData TransformUnit::ReadVertex(const VertexReader &vreader, const Tran
if (state.readUV) {
vreader.ReadUV(vertex.v.texturecoords.AsArray());
vertex.v.texturecoords.q() = 0.0f;
if (state.geUVScale) {
// The decoder only normalized them (8 and 16 bit UVs are unsigned).
for (int i = 0; i < 2; ++i) {
const float scaled = ProductToFloat24((double)TruncateToFloat24(vertex.v.texturecoords[i]) * state.uvScale[i]);
vertex.v.texturecoords[i] = TruncateToFloat24(GEAdd(scaled, state.uvOffset[i]));
}
}
lastTC = vertex.v.texturecoords;
} else {
vertex.v.texturecoords = lastTC;
@@ -669,7 +691,7 @@ public:
GetIndexBounds(indices, vertex_count, vertex_type, &lowerBound_, &upperBound_);
if (vertex_count != 0) {
const int count = upperBound_ - lowerBound_ + 1;
const UVScale uvScale = LoadUVScaleOffset(gstate);
const UVScale uvScale = UsesGEUVScale(vertex_type) ? UVScale{ 1.0f, 1.0f, 0.0f, 0.0f } : LoadUVScaleOffset(gstate);
vdecoder.DecodeVerts(base, (const u8 *)vertices + vdecoder.VertexSize() * lowerBound_, &uvScale, count);
}