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Document an obscure bug in J3DGDSetTexCoordScale2

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LagoLunatic
2024-06-24 23:21:48 -04:00
parent f9d40ebad8
commit 93a883fabf
1 changed files with 3 additions and 0 deletions
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src/JSystem/J3DGraphBase/J3DGD.cpp
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@@ -278,6 +278,9 @@ void J3DGDSetTexCoordGen(GXTexGenType type, GXTexGenSrc src) {
void J3DGDSetTexCoordScale2(GXTexCoordID id, u16 scaleS, u8 biasS, u8 wrapS, u16 scaleT, u8 biasT, u8 wrapT) {
GDOverflowCheck(15);
J3DGDWriteBPCmd(0xFE03FFFF);
// Bug: When id is GX_TEXCOORD_NULL (0xFF), the calculation below winds up producing the wrong
// BP register ID. Instead of a SU_SSIZE and SU_TSIZE register, it effectively negatively
// overflows to the previous registers: RAS1_TREF6 and RAS1_TREF7, potentially corrupting them.
J3DGDWriteBPCmd((scaleS - 1) | (biasS << 16) | (wrapS << 17) | (0x30 + id * 2) << 24);
J3DGDWriteBPCmd((scaleT - 1) | (biasT << 16) | (wrapT << 17) | (0x31 + id * 2) << 24);
}