ref: b31e965ea36f21cf4da91ae33d840999e10a76d4
dir: /sys/src/libmemdraw/alpha.hoc/
func f(x) {
return x-x%1
}
func pixel(dr, dg, db, da, sr, sg, sb, sa, m) {
M = 255-f((sa*m)/255)
print f((sr*m+dr*M)/255), " ", f((sg*m+dg*M)/255), " ", f((sb*m+db*M)/255), " ", f((sa*m+da*M)/255), "\n"
return 0
}