anchor.diff:    ;; RAX = Source pixel.
     ;; RCX = Alpha channel of source pixel at (byte 8 24).
     ;; RDX = Dest pixel.
  -  (sys.lap-x86:shr32 :ebx 24) ; EBX = alpha (000A)
  +  (sys.lap-x86:shr32 :ecx 24) ; ECX = alpha (000A)
     (sys.lap-x86:movd :mm0 :eax) ; MM0 = source (0000ARGB)
  -  (sys.lap-x86:movd :mm1 :ebx) ; MM1 = source alpha (0000000A)
  -  (sys.lap-x86:movd :mm2 :edx) ; MM2 = dest (0000XRGB)
  +  (sys.lap-x86:movd :mm1 :ecx) ; MM1 = source alpha (0000000A)
  +  (sys.lap-x86:movd :mm2 :edx) ; MM2 = dest (0000ARGB)
     (sys.lap-x86:pxor :mm3 :mm3) ; MM3 = 0
     ;; Swizzle alpha.
  -  (sys.lap-x86:pmuludq :mm1 (:rip alpha-shuffle)) ; MM1 = source alpha (0000AAAA)
  -  (sys.lap-x86:punpcklbw :mm1 :mm3) ; MM1 = source alpha (0A0A0A0A)
  +  (sys.lap-x86:pmuludq :mm1 (:rip alpha-shuffle)) ; MM1 = source alpha (00000AAA)
  +  (sys.lap-x86:punpcklbw :mm1 :mm3) ; MM1 = source alpha (000A0A0A)
     ;; Compute inverse alpha.
     (sys.lap-x86:movq :mm4 (:rip inverse-alpha))
     (sys.lap-x86:psubb :mm4 :mm1) ; MM4 = (- 255 alpha)
  
positive.code: ;;; EAX = ARGB8888 pixel.
  ;;; RDI = XRGB8888 destination.
  ;;; Alpha-blend PIXEL into DEST.
  ;;; Uses OpenGL-style Src-alpha/One-minus-src-alpha blending.
  (sys.int::define-lap-function %%alpha-blend-one-argb8888-xrgb8888 ()
    (sys.lap-x86:mov32 :ebx :eax) ; ebx = pixel (ARGB)
    (sys.lap-x86:and32 :ebx #xFF000000) ; ebx = pixel-alpha (A000)
    (sys.lap-x86:jz out) ; Fully transparent, bail out.
    (sys.lap-x86:cmp32 :ebx #xFF000000)
    (sys.lap-x86:je set-result) ; Fully opaque, just set it.
    ;; Read destination.
    (sys.lap-x86:mov32 :edx (:rdi)) ; rdx = pixel (XRGB)
  
negative.code:   (sys.lap-x86:ret)
    ;(:align 4) ; 16 byte alignment for XMM. (TODO)
    alpha-shuffle
    (:d64/le #x0000000000010101)
    inverse-alpha
    (:d64/le #x00FF00FF00FF00FF)
    round-thingy
  