Here's the assembly code for my alpha-blending routine:
ubyte[4] src = *cast(ubyte[4]*)(palette.ptr + 4 * *c);
ubyte[4] *p = cast(ubyte[4]*)(workpad + (offsetX + x)*4 +
offsetY);
asm{ //moving the values to their destinations
movd MM0, p;
movd MM1, src;
movq MM5, alpha;
movq MM7, alphaMMXmul_const1;
movq MM6, alphaMMXmul_const2;
punpcklbw MM2, MM0;
punpcklbw MM3, MM1;
paddw MM6, MM5; //1 + alpha
psubw MM7, MM5; //256 - alpha
pmulhuw MM2, MM6; //src * (1 + alpha)
pmulhuw MM3, MM7; //dest * (256 - alpha)
paddw MM3, MM2; //(src * (1 + alpha)) + (dest * (256 - alpha))
psrlw MM3, 8; //(src * (1 + alpha)) + (dest * (256 - alpha)) /
256
//moving the result to its place;
packuswb MM4, MM3;
movd p, MM4;
emms;
}
The two constants being referred here:
static immutable ushort[4] alphaMMXmul_const1 = [256,256,256,256];
static immutable ushort[4] alphaMMXmul_const2 = [1,1,1,1];
alpha is a ushort[4] containing the alpha value four times.
After some debugging, I found out that the p pointer becomes null
at the end instead of pointing to a value. I have no experience
with using in-line assemblers (although I made a few Hello World
programs for MS-Dos with a stand-alone assembler), so I don't
know when and how the compiler will interpret the types from D.
