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Can you do destination alpha reads from the frame buffer?

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Hello. I hope someone can help me with this. There was some running code that did an alpha blend using the destination alpha of the render target, which was simply the back buffer of the display surface. This was on an ATI card. However, all the dest alpha reads on my new NVidia card (GF4MX) simply act as if the dest alpha was a uniform one. I posted the same topic before, but with a different slant becaue I asumed something might be wrong with my card or somethin. But the code produces the same "error" on the reference driver (as someone suggested). It was also suggested that destination alpha reads could only be performed on a render-to-texture setup. I would really like to steer away from this if at all possible, to avoid the extra copy. Also, some cards do not support large, oddly shaped textures nessesary to reproduce the dimentions of the frame buffer. A lot of cards don't support render-to-texture at all, or at least not very well. There are ways around all this, I know, but I'm trying to determine if I'm missing something that might give a clean, simple solution to this. Does anyone know if it is a defined operation to perform destination alpha reads from the back-buffer of the display surface? If not, can you point me to some links on how to best support destination alpha reads (I couldn't find anything in the forums or the articles)? Thanks for your help. [edited by - SH on June 5, 2002 1:52:03 PM]

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