Ian Romanick wrote:
As I mentioned in a couple earlier threads, there are some problems with enabling this extension in a couple different drivers. Because of that I have not committed any device-dependent code. Attached to this message are the patches to the Radeon and MGA drivers to enable SGI_make_current_read. I expect similar patches will be needed for the other drivers. The MGA patch seems okay, but I have not had a chance to test it much. The Radeon patch has several problems with both xdemos/wincopy from Mesa and my patched glxgears (see the previous thread for that patch).
I took a quick at this problem again last night. I'm a bit confused by spantmp.h and how it interacts with Mesa. The generated functions get used, for example, by _mesa_read_rgba_span. This function gets used in all the expected places: CopyTexImage, ReadPixels, etc. However, it also gets used by _mesa_blend_span and a few other places that use the ctx->DrawBuffer.
The problem is that the information about which buffer is needed (i.e., read or draw) is NOT passed into swrast->Driver.ReadRGBASpan. How does even the software rasterizer work correctly? Won't there be problems with alpha blending if the read-drawable is set to something different from the draw-drawable?
The SetBuffer() function (seen in swrast.h) will get called as needed to switch between the draw buffer (for blending) and the read buffer (for glRead/CopyPixels, glCopyTexImage, etc).
-Brian
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