Faster Quake 2 ref_soft
Posted: Thu May 01, 2014 4:45 am
Yes, everyone has been clamoring for a faster software rendered Quake 2 experience, and it's finally here! Also the years of shame will end. Speaking of course about 'D_DrawSpans16' which is really only 'D_DrawSpans8'. Anyway, this is simply a cut-and-paste almost identical to the Quake 1 D_DrawSpans16 discussed elsewhere on this board.
Compared to the original C implementation, the fps improvement is immediately noticable. Since no one will actually use, much less test, this tutorial, let's say it is 2x speed of the original function. Compared to the asm version I would expect speed to be similar. Well-crafted C can come close to the asm code and in some cases produce identical output.
Instructions- pick a Quake 2 port that hasn't forsaken ref_soft (I'd suggest Knigtmare's 3.24) and simply cut-and-paste over D_DrawSpans16 in r_scan.c:
Compared to the original C implementation, the fps improvement is immediately noticable. Since no one will actually use, much less test, this tutorial, let's say it is 2x speed of the original function. Compared to the asm version I would expect speed to be similar. Well-crafted C can come close to the asm code and in some cases produce identical output.
Instructions- pick a Quake 2 port that hasn't forsaken ref_soft (I'd suggest Knigtmare's 3.24) and simply cut-and-paste over D_DrawSpans16 in r_scan.c:
Code: Select all
/*
=============
D_DrawSpans16
FIXME: actually make this subdivide by 16 instead of 8!!! qb: OK!!!!
=============
*/
/*==============================================
//unrolled- mh, MK, qbism
//============================================*/
static int count, spancount;
static byte *pbase, *pdest;
static fixed16_t s, t, snext, tnext, sstep, tstep;
static float sdivz, tdivz, zi, z, du, dv, spancountminus1;
static float sdivzstepu, tdivzstepu, zistepu;
static int izi, izistep; // mankrip
static short *pz; // mankrip
//qbism: pointer to pbase and macroize idea from mankrip
#define WRITEPDEST(i) { pdest[i] = *(pbase + (s >> 16) + (t >> 16) * cachewidth); s+=sstep; t+=tstep;}
void D_DrawSpans16(espan_t *pspan) //qb: up it from 8 to 16. This + unroll = big speed gain!
{
sstep = 0; // keep compiler happy
tstep = 0; // ditto
pbase = (byte *)cacheblock;
sdivzstepu = d_sdivzstepu * 16;
tdivzstepu = d_tdivzstepu * 16;
zistepu = d_zistepu * 16;
do
{
pdest = (byte *)((byte *)d_viewbuffer + (r_screenwidth * pspan->v) + pspan->u);
count = pspan->count >> 4;
spancount = pspan->count % 16;
// calculate the initial s/z, t/z, 1/z, s, and t and clamp
du = (float)pspan->u;
dv = (float)pspan->v;
sdivz = d_sdivzorigin + dv*d_sdivzstepv + du*d_sdivzstepu;
tdivz = d_tdivzorigin + dv*d_tdivzstepv + du*d_tdivzstepu;
zi = d_ziorigin + dv*d_zistepv + du*d_zistepu;
z = (float)0x10000 / zi; // prescale to 16.16 fixed-point
s = (int)(sdivz * z) + sadjust;
if (s < 0) s = 0;
else if (s > bbextents) s = bbextents;
t = (int)(tdivz * z) + tadjust;
if (t < 0) t = 0;
else if (t > bbextentt) t = bbextentt;
while (count-- > 0) // Manoel Kasimier
{
sdivz += sdivzstepu;
tdivz += tdivzstepu;
zi += zistepu;
z = (float)0x10000 / zi; // prescale to 16.16 fixed-point
snext = (int)(sdivz * z) + sadjust;
if (snext < 16) snext = 16;
else if (snext > bbextents) snext = bbextents;
tnext = (int)(tdivz * z) + tadjust;
if (tnext < 16) tnext = 16;
else if (tnext > bbextentt) tnext = bbextentt;
sstep = (snext - s) >> 4;
tstep = (tnext - t) >> 4;
pdest += 16;
WRITEPDEST(-16);
WRITEPDEST(-15);
WRITEPDEST(-14);
WRITEPDEST(-13);
WRITEPDEST(-12);
WRITEPDEST(-11);
WRITEPDEST(-10);
WRITEPDEST(-9);
WRITEPDEST(-8);
WRITEPDEST(-7);
WRITEPDEST(-6);
WRITEPDEST(-5);
WRITEPDEST(-4);
WRITEPDEST(-3);
WRITEPDEST(-2);
WRITEPDEST(-1);
s = snext;
t = tnext;
}
if (spancount > 0)
{
spancountminus1 = (float)(spancount - 1);
sdivz += d_sdivzstepu * spancountminus1;
tdivz += d_tdivzstepu * spancountminus1;
zi += d_zistepu * spancountminus1;
z = (float)0x10000 / zi; // prescale to 16.16 fixed-point
snext = (int)(sdivz * z) + sadjust;
if (snext < 16) snext = 16;
else if (snext > bbextents) snext = bbextents;
tnext = (int)(tdivz * z) + tadjust;
if (tnext < 16) tnext = 16;
else if (tnext > bbextentt) tnext = bbextentt;
if (spancount > 1)
{
sstep = (snext - s) / (spancount - 1);
tstep = (tnext - t) / (spancount - 1);
}
pdest += spancount;
switch (spancount)
{
case 16:
WRITEPDEST(-16);
case 15:
WRITEPDEST(-15);
case 14:
WRITEPDEST(-14);
case 13:
WRITEPDEST(-13);
case 12:
WRITEPDEST(-12);
case 11:
WRITEPDEST(-11);
case 10:
WRITEPDEST(-10);
case 9:
WRITEPDEST(-9);
case 8:
WRITEPDEST(-8);
case 7:
WRITEPDEST(-7);
case 6:
WRITEPDEST(-6);
case 5:
WRITEPDEST(-5);
case 4:
WRITEPDEST(-4);
case 3:
WRITEPDEST(-3);
case 2:
WRITEPDEST(-2);
case 1:
WRITEPDEST(-1);
break;
}
}
} while ((pspan = pspan->pnext) != NULL);
}