Path: utzoo!attcan!uunet!husc6!rutgers!rochester!pt.cs.cmu.edu!andrew.cmu.edu!bader+
From: bader+@andrew.cmu.edu (Miles Bader)
Newsgroups: comp.sys.amiga
Subject: graphics chips ideas
Message-ID: <0Wz-V=Au8k-083IFce@andrew.cmu.edu>
Date: 7 Aug 88 18:58:19 GMT
Organization: Carnegie Mellon
Lines: 14

Currently, as I understand it, in instances where you want a
background to show through (like with sprites, or in dual-playfield
mode), a particular color register indicates "see-through."

I think a neat way to do it would to be eliminate the special
behavior of that register, and add another 4 bits to ALL the color
registers (for a total of 16 bits each), which would be "opaqueness":
a value of 0 would mean "completely transparent," and a value of 15
would mean completely opaque.  The color of a pixel would be
(fg*op)+(bg*(15-op)) for each of red, blue and green, where op is the
opaqueness, fg is the intensity of this layer, and bg is the
intensity of the underlying layer.

-Miles