No support for `gSPFogPosition` command & inaccurate combine/LERP about n64

[glankk]

Issue 1 happens because gfxdis is rejecting SPFogPosition macros with a zero in the z multiplier as invalid, since there's no input in the normal range that can produce that output. This has been fixed in libgfxd, where a macro with invalid values for SPFogPosition is replaced by an equivalent SPFogFactor. I'll port the fix over to gfxdis.

For issue 2, substituting -0x7C8 for the second half of the input produces the correct output:

$ gfxdis.f3dex -d FC127FFF FFFFF838
{
    gsDPSetCombineMode(G_CC_MODULATEI, G_CC_PASS2),
}

Note that G_CC_MODULATEI is equivalent to G_CC_MODULATERGB, and FFFFF838 is equal to -0x7C8.

[MegaMech]

Should I be using libgfxd instead of gfxdis?

[glankk]

No, libgfxd is just a library based on gfxdis, but its a separate thing at the moment when ideally gfxdis would be built on top of libgfxd.