README - DOOM assembly code
Okay, I add the DOS assembly module for the historically inclined here (may rec.games.programmer suffer). If anyone feels the urge to port these to GNU GCC; either inline or as separate modules including Makefile support, be my guest.
Module tmap.S includes the inner loops for texture mapping, the interesting one being the floor/ceiling span rendering.
There was another module in the source dump, fpfunc.S, that had both texture mapping and fixed point functions. It contained implementations both for i386 and M68k. For brevity, I include only the i386 fixed point stuff below.
//==================================================== // tmap.S as of January 10th, 1997
//================ // // R_DrawColumn // //================
.dataloopcount .long 0 pixelcount .long 0
.text
.align 16.globl _R_DrawColumn _R_DrawColumn:
pushad
movl ebp,[_dc_yl]
movl ebx,ebp
movl edi,[_ylookup+ebx*4]
movl ebx,[_dc_x]
addl edi,[_columnofs + ebx*4]
movl eax,[_dc_yh]
incl eax
subl eax,ebp // pixel count
movl [pixelcount],eax // save for final pixel
js done // nothing to scale
shrl eax,1 // double pixel count
movl [loopcount],eax
movl ecx,[_dc_iscale]
movl eax,[_centery]
subl eax,ebp
imull ecx
movl ebp,[_dc_texturemid]
subl ebp,eax
shll ebp,9 // 7 significant bits, 25 frac
movl esi,[_dc_source]
movl ebx,[_dc_iscale]
shll ebx,9
movl eax,OFFSET patch1+2 // convice tasm to modify code...
movl [eax],ebx
movl eax,OFFSET patch2+2 // convice tasm to modify code...
movl [eax],ebx// eax aligned colormap // ebx aligned colormap // ecx,edx scratch // esi virtual source // edi moving destination pointer // ebp frac
movl ecx,ebp // begin calculating first pixel
addl ebp,ebx // advance frac pointer
shrl ecx,25 // finish calculation for first pixel
movl edx,ebp // begin calculating second pixel
addl ebp,ebx // advance frac pointer
shrl edx,25 // finish calculation for second pixel
movl eax,[_dc_colormap]
movl ebx,eax
movb al,[esi+ecx] // get first pixel
movb bl,[esi+edx] // get second pixel
movb al,[eax] // color translate first pixel
movb bl,[ebx] // color translate second pixel
testl [pixelcount],0fffffffeh
jnz doubleloop // at least two pixels to map
jmp checklast
.align 16doubleloop: movl ecx,ebp // begin calculating third pixel patch1: addl ebp,12345678h // advance frac pointer movb [edi],al // write first pixel shrl ecx,25 // finish calculation for third pixel movl edx,ebp // begin calculating fourth pixel patch2: addl ebp,12345678h // advance frac pointer movl [edi+SCREENWIDTH],bl // write second pixel shrl edx,25 // finish calculation for fourth pixel movb al,[esi+ecx] // get third pixel addl edi,SCREENWIDTH*2 // advance to third pixel destination movb bl,[esi+edx] // get fourth pixel decl [loopcount] // done with loop? movb al,[eax] // color translate third pixel movb bl,[ebx] // color translate fourth pixel jnz doubleloop
// check for final pixel checklast: testl [pixelcount],1 jz done movb [edi],al // write final pixel
done: popad ret
//================ // // R_DrawSpan // // Horizontal texture mapping // //================
.align 16.globl _R_DrawSpan _R_DrawSpan: pushad
//
// find loop count
//
movl eax,[_ds_x2]
incl eax
subl eax,[_ds_x1] // pixel count
movl [pixelcount],eax // save for final pixel
js hdone // nothing to scale
shrl eax,1 // double pixel count
movl [loopcount],eax
// // build composite position // movl ebp,[_ds_xfrac] shll ebp,10 andl ebp,0ffff0000h movl eax,[_ds_yfrac] shrl eax,6 andl eax,0ffffh orl ebp,eax
movl esi,[_ds_source]// // calculate screen dest // movl edi,[_ds_y] movl edi,[_ylookup+edi4] movl eax,[_ds_x1] addl edi,[_columnofs+eax4]
// // build composite step // movl ebx,[_ds_xstep] shll ebx,10 andl ebx,0ffff0000h movl eax,[_ds_ystep] shrl eax,6 andl eax,0ffffh orl ebx,eax
movl eax,OFFSET hpatch1+2 // convice tasm to modify code...
movl [eax],ebx
movl eax,OFFSET hpatch2+2 // convice tasm to modify code...
movl [eax],ebx// eax aligned colormap // ebx aligned colormap // ecx,edx scratch // esi virtual source // edi moving destination pointer // ebp frac
shldl ecx,ebp,22 // begin calculating third pixel (y units)
shldl ecx,ebp,6 // begin calculating third pixel (x units)
addl ebp,ebx // advance frac pointer
andl ecx,4095 // finish calculation for third pixel
shldl edx,ebp,22 // begin calculating fourth pixel (y units)
shldl edx,ebp,6 // begin calculating fourth pixel (x units)
addl ebp,ebx // advance frac pointer
andl edx,4095 // finish calculation for fourth pixel
movl eax,[_ds_colormap]
movl ebx,eax
movb al,[esi+ecx] // get first pixel
movb bl,[esi+edx] // get second pixel
movb al,[eax] // color translate first pixel
movb bl,[ebx] // color translate second pixel
testl [pixelcount],0fffffffeh
jnz hdoubleloop // at least two pixels to map
jmp hchecklast
.align 16hdoubleloop: shldl ecx,ebp,22 // begin calculating third pixel (y units) shldl ecx,ebp,6 // begin calculating third pixel (x units) hpatch1: addl ebp,12345678h // advance frac pointer movb [edi],al // write first pixel andl ecx,4095 // finish calculation for third pixel shldl edx,ebp,22 // begin calculating fourth pixel (y units) shldl edx,ebp,6 // begin calculating fourth pixel (x units) hpatch2: addl ebp,12345678h // advance frac pointer movb [edi+1],bl // write second pixel andl edx,4095 // finish calculation for fourth pixel movb al,[esi+ecx] // get third pixel addl edi,2 // advance to third pixel destination movb bl,[esi+edx] // get fourth pixel decl [loopcount] // done with loop? movb al,[eax] // color translate third pixel movb bl,[ebx] // color translate fourth pixel jnz hdoubleloop
// check for final pixel hchecklast: testl [pixelcount],1 jz hdone movb [edi],al // write final pixel
hdone: popad ret
//==================================================== // fpfunc.S as of January 10th, 1997 (parts)
.text
.align 4
.globl _FixedMul
_FixedMul:
pushl %ebp
movl %esp,%ebp
movl 8(%ebp),%eax
imull 12(%ebp)
shrdl $16,%edx,%eax
popl %ebp
ret
.align 4.globl _FixedDiv2 _FixedDiv2: pushl %ebp movl %esp,%ebp movl 8(%ebp),%eax cdq shldl $16,%eax,%edx sall $16,%eax idivl 12(%ebp) popl %ebp ret