ref: c175fd8cdf3b905bb27b2bbc7d09db825d7c1516
dir: /src/ztriangle.h/
/*
* An eXtReMeLy complicated, delicate, tuned triangle rasterizer
* Aight, so basically this is the most complicated code you'll ever read in your life.
* The lifetime of variables has been... SUPER Optimized, that's why there's so many random ass curly braces everywhere.
* Yes, it is necessary to do that. This code is extremely delicate
* and even a minor fuck-up is gonna tank the framerate
Before committing any changes, run gears, model, and texture on your changed code to make sure you didn't
fuck up!
Things to keep in mind:
1) Tight control of the lifetimes, scopes, and usage of variables lets us use registers more often and memory less
2) Doing the same operation on multiple items is faster than doing different things on different items, generally, because
they will be able to take advantage of any/all applicable SIMD/vector ops on your hardware.
3) Divide operations are vastly more expensive than add/sub/bitwise/etc
4) Bit shifting is your friend, it's the fast way to multiply or divide by 2.
5) Fixed point math is used for the depth "z" buffer
6) We're not just using floats for everything because this is still supposed to be fast on platforms without SSE2
7) Fewer variables is usually better
*/
{
GLfloat fdx1, fdx2, fdy1, fdy2;
GLushort* pz1;
PIXEL* pp1;
GLint dx1, dy1, dx2, dy2;
#if TGL_FEATURE_POLYGON_STIPPLE == 1
GLushort the_y;
#endif
GLint error, derror;
GLint x1, dxdy_min, dxdy_max;
/* warning: x2 is multiplied by 2^16 */
GLint x2, dx2dy2;
#ifdef INTERP_Z
GLint z1, dzdx, dzdy, dzdl_min, dzdl_max;
#endif
#ifdef INTERP_RGB
GLint r1, drdx, drdy, drdl_min, drdl_max;
GLint g1, dgdx, dgdy, dgdl_min, dgdl_max;
GLint b1, dbdx, dbdy, dbdl_min, dbdl_max;
#endif
#ifdef INTERP_ST
GLint s1, dsdx, dsdy, dsdl_min, dsdl_max;
GLint t1, dtdx, dtdy, dtdl_min, dtdl_max;
#endif
#ifdef INTERP_STZ
GLfloat sz1, dszdx, dszdy, dszdl_min, dszdl_max;
GLfloat tz1, dtzdx, dtzdy, dtzdl_min, dtzdl_max;
GLfloat fdzdx, fndzdx, ndszdx, ndtzdx;
#endif
/* we sort the vertex with increasing y */
if (p1->y < p0->y) {
ZBufferPoint *t = p0;
p0 = p1;
p1 = t;
}
if (p2->y < p0->y) {
ZBufferPoint *t = p2;
p2 = p1;
p1 = p0;
p0 = t;
} else if (p2->y < p1->y) {
ZBufferPoint *t = p1;
p1 = p2;
p2 = t;
}
/* we compute dXdx and dXdy for all GLinterpolated values */
fdx1 = p1->x - p0->x;//fdx1 first usage (VALUE_FDX1_USED)
fdy1 = p1->y - p0->y;//fdy1 first usage (VALUE_FDY1_USED)
fdx2 = p2->x - p0->x;
fdy2 = p2->y - p0->y;
GLfloat fz = fdx1 * fdy2 - fdx2 * fdy1;//fz first usage
if (fz == 0)
return;
fz = 1.0 / fz; //value of fz is used (VALUE_FZ_USED)
//for these (VALUE_FZ_USED)
fdx1 *= fz;
fdy1 *= fz;
fdx2 *= fz;
fdy2 *= fz;
//and then
{
GLfloat d1, d2;
#ifdef INTERP_Z
{
d1 = p1->z - p0->z; //d1 first usage
d2 = p2->z - p0->z;
dzdx = (GLint)(fdy2 * d1 - fdy1 * d2);
dzdy = (GLint)(fdx1 * d2 - fdx2 * d1);
}
#endif
#ifdef INTERP_RGB
{
d1 = p1->r - p0->r;
d2 = p2->r - p0->r;
drdx = (GLint)(fdy2 * d1 - fdy1 * d2);
drdy = (GLint)(fdx1 * d2 - fdx2 * d1);
}
{
d1 = p1->g - p0->g;
d2 = p2->g - p0->g;
dgdx = (GLint)(fdy2 * d1 - fdy1 * d2);
dgdy = (GLint)(fdx1 * d2 - fdx2 * d1);
}
{
d1 = p1->b - p0->b;
d2 = p2->b - p0->b;
dbdx = (GLint)(fdy2 * d1 - fdy1 * d2);
dbdy = (GLint)(fdx1 * d2 - fdx2 * d1);
}
#endif
#ifdef INTERP_ST
{
d1 = p1->s - p0->s;
d2 = p2->s - p0->s;
dsdx = (GLint)(fdy2 * d1 - fdy1 * d2);
dsdy = (GLint)(fdx1 * d2 - fdx2 * d1);
}
{
d1 = p1->t - p0->t;
d2 = p2->t - p0->t;
dtdx = (GLint)(fdy2 * d1 - fdy1 * d2);
dtdy = (GLint)(fdx1 * d2 - fdx2 * d1);
}
#endif
#ifdef INTERP_STZ
{
GLfloat zedzed;
zedzed = (GLfloat)p0->z;
p0->sz = (GLfloat)p0->s * zedzed;
p0->tz = (GLfloat)p0->t * zedzed;
zedzed = (GLfloat)p1->z;
p1->sz = (GLfloat)p1->s * zedzed;
p1->tz = (GLfloat)p1->t * zedzed;
zedzed = (GLfloat)p2->z;
p2->sz = (GLfloat)p2->s * zedzed;
p2->tz = (GLfloat)p2->t * zedzed;
}
{
d1 = p1->sz - p0->sz;
d2 = p2->sz - p0->sz;
dszdx = (fdy2 * d1 - fdy1 * d2);
dszdy = (fdx1 * d2 - fdx2 * d1);
}
{
d1 = p1->tz - p0->tz;
d2 = p2->tz - p0->tz;
dtzdx = (fdy2 * d1 - fdy1 * d2);
dtzdy = (fdx1 * d2 - fdx2 * d1);
}
#endif
} //EOF d1, d2 lifetimes.
/* screen coordinates */
pp1 = (PIXEL*)(zb->pbuf) + zb->xsize * p0->y; //pp1 first usage
#if TGL_FEATURE_POLYGON_STIPPLE == 1
the_y = p0->y;
#endif
pz1 = zb->zbuf + p0->y * zb->xsize;
DRAW_INIT();
//part used here and down.
//TODO: #pragma omp parallel for private(a, b, c)
//Required reading:
//http://jakascorner.com/blog/2016/06/omp-data-sharing-attributes.html
//I'd also like to figure out if the main while() loop over raster lines can be OMP parallelized, but I suspect it isn't worth it.
for (GLint part = 0; part < 2; part++) {
GLint nb_lines;
{ZBufferPoint *pr1, *pr2, *l1, *l2; //BEGINNING OF LIFETIME FOR ZBUFFERPOINT VARS!!!
register GLint update_left, update_right; //update_left decl
if (part == 0) {
if (fz > 0) { //Here! (VALUE_FZ_USED)
update_left = 1; //update_left first usage.
update_right = 1;
l1 = p0; //MARK l1 first usage
l2 = p2; //MARK l2 first usage
pr1 = p0; //MARK first usage of pr1
pr2 = p1; //MARK first usage pf pr2
} else {
update_left = 1; //update_left second usage.
update_right = 1;
l1 = p0;
l2 = p1;
pr1 = p0;
pr2 = p2;
}
nb_lines = p1->y - p0->y;
} else { //SECOND PART~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/* second part */
if (fz > 0) { //fz last usage (VALUE_FZ_USED)
update_left = 0; //update left third usage.
update_right = 1;
pr1 = p1;
pr2 = p2;
} else {
update_left = 1; //4th
update_right = 0;
l1 = p1;
l2 = p2;
}
nb_lines = p2->y - p1->y + 1;
} //EOF SECOND PART
/* compute the values for the left edge */
//pr1 and pr2 are not used inside this area.
if (update_left) { //5th usage
{
register GLint tmp;
dy1 = l2->y - l1->y;
dx1 = l2->x - l1->x;
if (dy1 > 0)
tmp = (dx1 << 16) / dy1;
else
tmp = 0;
x1 = l1->x;
error = 0;
derror = tmp & 0x0000ffff;
dxdy_min = tmp >> 16;
}
dxdy_max = dxdy_min + 1;
#ifdef INTERP_Z
z1 = l1->z;
dzdl_min = (dzdy + dzdx * dxdy_min);
dzdl_max = dzdl_min + dzdx;
#endif
#ifdef INTERP_RGB
r1 = l1->r;
drdl_min = (drdy + drdx * dxdy_min);
drdl_max = drdl_min + drdx;
g1 = l1->g;
dgdl_min = (dgdy + dgdx * dxdy_min);
dgdl_max = dgdl_min + dgdx;
b1 = l1->b;
dbdl_min = (dbdy + dbdx * dxdy_min);
dbdl_max = dbdl_min + dbdx;
#endif
#ifdef INTERP_ST
s1 = l1->s;
dsdl_min = (dsdy + dsdx * dxdy_min);
dsdl_max = dsdl_min + dsdx;
t1 = l1->t;
dtdl_min = (dtdy + dtdx * dxdy_min);
dtdl_max = dtdl_min + dtdx;
#endif
#ifdef INTERP_STZ
sz1 = l1->sz;
dszdl_min = (dszdy + dszdx * dxdy_min);
dszdl_max = dszdl_min + dszdx;
tz1 = l1->tz;
dtzdl_min = (dtzdy + dtzdx * dxdy_min);
dtzdl_max = dtzdl_min + dtzdx;
#endif
} //EOF update left
//Is l1 used after update_left?
/* compute values for the right edge */
if (update_right) { //Update right tested
dx2 = (pr2->x - pr1->x);
dy2 = (pr2->y - pr1->y); //LAST USAGE OF PR2
if (dy2 > 0)
dx2dy2 = (dx2 << 16) / dy2;
else
dx2dy2 = 0;
x2 = pr1->x << 16; //LAST USAGE OF PR1
} //EOF update right
} //End of lifetime for ZBufferpoints
/* we draw all the scan line of the part */
while (nb_lines > 0) {
nb_lines--;
#ifndef DRAW_LINE
/* generic draw line */
{
register PIXEL* pp;
register GLint n;
#ifdef INTERP_Z
register GLushort* pz;
register GLuint z;
#endif
#ifdef INTERP_RGB
register GLint or1, og1, ob1;
#endif
#ifdef INTERP_ST
register GLuint s, t;
#endif
#ifdef INTERP_STZ
//GLfloat sz, tz; //These variables go unused in this draw line function.
#endif
n = (x2 >> 16) - x1;
//pp = (PIXEL*)((GLbyte*)pp1 + x1 * PS_ZB);
pp = (PIXEL*)pp1 + x1;
#ifdef INTERP_Z
pz = pz1 + x1;
z = z1;
#endif
#ifdef INTERP_RGB
or1 = r1;
og1 = g1;
ob1 = b1;
#endif
#ifdef INTERP_ST
s = s1;
t = t1;
#endif
#ifdef INTERP_STZ
// sz = sz1; //What is SZ used for?
// tz = tz1; //What is TZ used for?
#endif
while (n >= 3) {
PUT_PIXEL(0); /*the_x++;*/
PUT_PIXEL(1); /*the_x++;*/
PUT_PIXEL(2); /*the_x++;*/
PUT_PIXEL(3); /*the_x++;*/
#ifdef INTERP_Z
pz += 4;
#endif
// pp = (PIXEL*)((GLbyte*)pp + 4 * PS_ZB);
pp += 4;
n -= 4;
}
while (n >= 0) {
PUT_PIXEL(0); /*the_x++;*/
#ifdef INTERP_Z
//pz += 1;
pz++;
#endif
/*pp = (PIXEL*)((GLbyte*)pp + PS_ZB);*/
pp++;
n--;
}
}
#else
DRAW_LINE();
#endif
/* left edge */
error += derror;
if (error > 0) {
error -= 0x10000;
x1 += dxdy_max;
#ifdef INTERP_Z
z1 += dzdl_max;
#endif
#ifdef INTERP_RGB
r1 += drdl_max;
g1 += dgdl_max;
b1 += dbdl_max;
#endif
#ifdef INTERP_ST
s1 += dsdl_max;
t1 += dtdl_max;
#endif
#ifdef INTERP_STZ
sz1 += dszdl_max;
tz1 += dtzdl_max;
#endif
} else {
x1 += dxdy_min;
#ifdef INTERP_Z
z1 += dzdl_min;
#endif
#ifdef INTERP_RGB
r1 += drdl_min;
g1 += dgdl_min;
b1 += dbdl_min;
#endif
#ifdef INTERP_ST
s1 += dsdl_min;
t1 += dtdl_min;
#endif
#ifdef INTERP_STZ
sz1 += dszdl_min;
tz1 += dtzdl_min;
#endif
}
/* right edge */
x2 += dx2dy2;
/* screen coordinates */
//pp1 = (PIXEL*)((GLbyte*)pp1 + zb->linesize);
pp1 += zb->xsize;
#if TGL_FEATURE_POLYGON_STIPPLE == 1
the_y++;
#endif
pz1 += zb->xsize;
}
}
}
#undef INTERP_Z
#undef INTERP_RGB
#undef INTERP_ST
#undef INTERP_STZ
#undef DRAW_INIT
#undef DRAW_LINE
#undef PUT_PIXEL