| EAX | Scratch register | |
| EBX | Scanline length | |
| ECX | 1/z | |
| EDX | Scratch register | |
| ESI | Pixel-buffer pixel address | |
| EBP | Span list pointer | |
| EDI | Z-buffer pixel address | |
| ESP | Stack pointer | |
| MM0 | Previous span (u0, v0) | |
| MM1 | Previous span (u1, v1) | |
| MM2 | Gouraud GB components | |
| MM3 | Gouraud AR components | |
| MM4 | Specular GB components | |
| MM5-MM7 | Scratch registers | |
| XMM0 | 1/w | |
| XMM1 | u0,v0,u1,v1 | |
| XMM2 | 1/w2 | |
| XMM3 | Left edge 1/w2 | |
| XMM4 | Left edge 1/w | |
| XMM5 | Left edge u0, v0, u1, v1 | |
| XMM6-XMM7 | Scratch registers |