Why ZOOMSPRITE, STRETCHSPRITE,ROTOSPRITE dosen't support Alpha blending?
doesn't? That's a bug. Give a small sample program and specify the platform you tested it.
Hmm it used to work fine, i havent check recently though...
Assuming it works:
the differences between 1 and -1 are very subtle, and you may not see those differences until you really have at least more than one or two image/object's overlapping one another.