void GGLAssembler::build_blend_factor(
integer_t& factor, int f, int component,
const pixel_t& dst_pixel,
integer_t& fragment,
integer_t& fb,
Scratch& scratches)
{
integer_t src_alpha(fragment);
// src_factor/dst_factor won't be used after blending,
// so it's fine to mark them as CORRUPTIBLE (if not aliased)
factor.flags |= CORRUPTIBLE;
switch(f) {
case GGL_ONE_MINUS_SRC_ALPHA:
case GGL_SRC_ALPHA:
if (component==GGLFormat::ALPHA && !isAlphaSourceNeeded()) {
// we're processing alpha, so we already have
// src-alpha in fragment, and we need src-alpha just this time.
} else {
// alpha-src will be needed for other components
if (!mBlendFactorCached || mBlendFactorCached==f) {
src_alpha = mAlphaSource;
factor = mAlphaSource;
factor.flags &= ~CORRUPTIBLE;
// we already computed the blend factor before, nothing to do.
if (mBlendFactorCached)
return;
// this is the first time, make sure to compute the blend
// factor properly.
mBlendFactorCached = f;
break;
} else {
// we have a cached alpha blend factor, but we want another one,
// this should really not happen because by construction,
// we cannot have BOTH source and destination
// blend factors use ALPHA *and* ONE_MINUS_ALPHA (because
// the blending stage uses the f/(1-f) optimization
// for completeness, we handle this case though. Since there
// are only 2 choices, this meens we want "the other one"
// (1-factor)
factor = mAlphaSource;
factor.flags &= ~CORRUPTIBLE;
RSB(AL, 0, factor.reg, factor.reg, imm((1<<factor.s)));
mBlendFactorCached = f;
return;
}
}
// fall-through...
case GGL_ONE_MINUS_DST_COLOR:
case GGL_DST_COLOR:
case GGL_ONE_MINUS_SRC_COLOR:
case GGL_SRC_COLOR:
case GGL_ONE_MINUS_DST_ALPHA:
case GGL_DST_ALPHA:
case GGL_SRC_ALPHA_SATURATE:
// help us find out what register we can use for the blend-factor
// CORRUPTIBLE registers are chosen first, or a new one is allocated.
if (fragment.flags & CORRUPTIBLE) {
factor.setTo(fragment.reg, 32, CORRUPTIBLE);
fragment.flags &= ~CORRUPTIBLE;
} else if (fb.flags & CORRUPTIBLE) {
factor.setTo(fb.reg, 32, CORRUPTIBLE);
fb.flags &= ~CORRUPTIBLE;
} else {
factor.setTo(scratches.obtain(), 32, CORRUPTIBLE);
}
break;
}
// XXX: doesn't work if size==1
switch(f) {
case GGL_ONE_MINUS_DST_COLOR:
case GGL_DST_COLOR:
factor.s = fb.s;
ADD(AL, 0, factor.reg, fb.reg, reg_imm(fb.reg, LSR, fb.s-1));
break;
case GGL_ONE_MINUS_SRC_COLOR:
case GGL_SRC_COLOR:
factor.s = fragment.s;
ADD(AL, 0, factor.reg, fragment.reg,
reg_imm(fragment.reg, LSR, fragment.s-1));
break;
case GGL_ONE_MINUS_SRC_ALPHA:
case GGL_SRC_ALPHA:
factor.s = src_alpha.s;
ADD(AL, 0, factor.reg, src_alpha.reg,
reg_imm(src_alpha.reg, LSR, src_alpha.s-1));
break;
case GGL_ONE_MINUS_DST_ALPHA:
case GGL_DST_ALPHA:
// XXX: should be precomputed
extract(factor, dst_pixel, GGLFormat::ALPHA);
ADD(AL, 0, factor.reg, factor.reg,
reg_imm(factor.reg, LSR, factor.s-1));
break;
case GGL_SRC_ALPHA_SATURATE:
// XXX: should be precomputed
// XXX: f = min(As, 1-Ad)
// btw, we're guaranteed that Ad's size is <= 8, because
// it's extracted from the framebuffer
break;
}
switch(f) {
case GGL_ONE_MINUS_DST_COLOR:
case GGL_ONE_MINUS_SRC_COLOR:
case GGL_ONE_MINUS_DST_ALPHA:
case GGL_ONE_MINUS_SRC_ALPHA:
RSB(AL, 0, factor.reg, factor.reg, imm((1<<factor.s)));
}
// don't need more than 8-bits for the blend factor
// and this will prevent overflows in the multiplies later
if (factor.s > 8) {
MOV(AL, 0, factor.reg, reg_imm(factor.reg, LSR, factor.s-8));
factor.s = 8;
}
}
