I’ve previously used the Vybrid processor. With that chip an “invisible” color could be created, and whenever that color was read from the fg buffer, it wasn’t written to the combined (bg/fg) buffer. For example, on startup, the fg buffer was filled using the invisible color and therefore was invisible (not written) when the buffers were combined. Bitmap images could then be written to the fg in regular colors making them visible. It appears this capability also exists in the IPU. What is the best way to implement it? Can an “invisible” color be created, or is it all done using the alpha channel? What is the best way to implement the fg? I'd rather not use a separate alpha buffer; however the interleaved alpha would be OK.
