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Reword a comment about early_ztest a bit.

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NeoBrainX 2013-01-08 16:51:01 +01:00
parent b06f30f845
commit c80f6e8b84
1 changed files with 8 additions and 11 deletions
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19
Source/Core/VideoCommon/Src/PixelShaderGen.cpp
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@ -1216,18 +1216,16 @@ static void WriteAlphaTest(char *&p, API_TYPE ApiType,DSTALPHA_MODE dstAlphaMode
WRITE(p, "ocol1 = 0;\n");
WRITE(p, "depth = 1.f;\n");
// HAXX: zcomploc is a way to control whether depth test is done before
// or after texturing and alpha test. PC GPU does depth test before texturing ONLY if depth value is
// not updated during shader execution.
// HAXX: zcomploc (aka early_ztest) is a way to control whether depth test is done before
// or after texturing and alpha test. PC GPUs have no way to support this
// feature properly as of 2012: depth buffer and depth test are not
// programmable and the depth test is always done after texturing.
// Most importantly, PC GPUs do not allow writing to the z buffer without
// writing a color value (unless color writing is disabled altogether).
// We implement "depth test before texturing" by discarding the fragment
// when the alpha test fail. This is not a correct implementation because
// even if the depth test fails the fragment could be alpha blended.
// this implemnetation is a trick to keep speed.
// the correct, but slow, way to implement a correct zComploc is :
// 1 - if zcomplock is enebled make a first pass, with color channel write disabled updating only
// depth channel.
// 2 - in the next pass disable depth chanel update, but proccess the color data normally
// this way is the only CORRECT way to emulate perfectly the zcomplock behaviour
// even if the depth test fails the fragment could be alpha blended, but
// we don't have a choice.
if (!(bpmem.zcontrol.early_ztest && bpmem.zmode.updateenable))
{
WRITE(p, "discard;\n");
@ -1236,7 +1234,6 @@ static void WriteAlphaTest(char *&p, API_TYPE ApiType,DSTALPHA_MODE dstAlphaMode
}
WRITE(p, "}\n");
}
static const char *tevFogFuncsTable[] =