No support for gSPFogPosition command & inaccurate combine/LERP

[MegaMech]

F3DEX1
Issue 1

Machine code: BC00000800000000

From hack64:

G_MW_FOG | 0x08 | Specifies the multiplier and offset for fog effects.

Byte-matching C code:

gSPFogPosition(gDisplayListHead++, (s16)0-1000, (s16)0-1000);

In mk64 the args match as two s16s. iirc they are minimum and maximum values for fog thickness.
Dunno if it actually asks for s16. That's just what mk64 does.

Issue 2
Mips to C output:

    temp_v0_11->unk4 = -0x7C8;
    temp_v0_11->unk0 = 0xFC127FFF;

gfxdis: FC127FFF00000000
output:

gDPSetCombineLERP(gDisplayListHead++, TEXEL0, COMBINED, SHADE, COMBINED, 0, COMBINED, 0, COMBINED, 0, COMBINED, 0, COMBINED, COMBINED, COMBINED, LOD_FRACTION, COMBINED);

Matching C:

gDPSetCombineMode(gDisplayListHead++, G_CC_MODULATERGB, G_CC_PASS2);

Note that G_CC_MODULATEIA appears to be the default flag that gfxdis outputs. This case required G_CC_MODULATERGB dunno if that's a thing that gfxdis can realize (I'm assuming not, so we can ignore that. Just wanted to point that out in-case that's important)

[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.