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3D: revise fog calculation to match hardware (emulate precision loss and overflow with big shifts)

This commit is contained in:
StapleButter 2017-08-16 22:20:53 +02:00
parent 0106406aff
commit bc1385e905
2 changed files with 14 additions and 9 deletions
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21
src/GPU3D_Soft.cpp
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@ -185,6 +185,8 @@ public:
// TODO: hardware tests show that this method is too precise
// I haven't yet figured out what the hardware does, though
if (w1factor==0 || w0factor==0) { yfactor = 0; return; }
s64 num = ((s64)x << (shift + 40)) / w1factor;
s64 denw0 = ((s64)(xdiff-x) << 40) / w0factor;
s64 denw1 = num >> shift;
@ -1590,25 +1592,28 @@ void ScanlineFinalPass(s32 y)
}
else
{
// technically: Z difference is shifted left by fog shift
// then bit 0-18 are the fractional part and bit 19-23 are the density index
// things are a little different here to avoid overflow in 32-bit range
// technically: Z difference is shifted right by two, then shifted left by fog shift
// then bit 0-16 are the fractional part and bit 17-31 are the density index
// on hardware, the final value can overflow the 32-bit range with a shift big enough,
// causing fog to 'wrap around' and accidentally apply to larger Z ranges
z -= fogoffset;
densityid = z >> (19-fogshift);
z = (z >> 2) << fogshift;
densityid = z >> 17;
if (densityid >= 32)
{
densityid = 32;
densityfrac = 0;
}
else
densityfrac = (z << fogshift) & 0x7FFFF;
densityfrac = z & 0x1FFFF;
}
// checkme
// checkme (may be too precise?)
u32 density =
((RenderFogDensityTable[densityid] * (0x80000-densityfrac)) +
(RenderFogDensityTable[densityid+1] * densityfrac)) >> 19;
((RenderFogDensityTable[densityid] * (0x20000-densityfrac)) +
(RenderFogDensityTable[densityid+1] * densityfrac)) >> 17;
if (density >= 127) density = 128;
u32 srccolor = ColorBuffer[pixeladdr];

2
src/NDSCart.cpp
View File

@ -618,7 +618,7 @@ void Write(u8 val, u32 hold)
default:
if (DataPos==0)
printf("unknown save SPI command %02X %02X\n", CurCmd, val);
printf("unknown save SPI command %02X %02X %d\n", CurCmd, val, islast);
break;
}