[Mesa-dev] glReadPixels broken w/ latest MapRenderbuffer changes

Brian Paul brianp at vmware.com
Fri Nov 4 15:02:56 PDT 2011

On 11/04/2011 03:48 PM, Eric Anholt wrote:
> On Fri, 04 Nov 2011 07:31:54 -0600, Brian Paul<brianp at vmware.com>  wrote:
>> The pure, non-DRI swrast driver dies in all glReadPixels calls when
>> reading from the front/back color buffers.  So basically all piglit
>> tests fail.
>> I think that the problem is there is no rb->Data for these surfaces;
>> they're XImages/Pixmaps.  The xlib driver needs to have
>> Map/UnmapRenderbuffer functions that can access the pixels in the
>> XImage/Pixmaps.
>> Sorry I didn't spot that before you pushed the series, Eric.
>> I may not be able to dig into this until later, or the weekend.
> Wow, the spans code for that driver is hideous.  Who still uses it?
> Also, color index?  Really?

Back when I first wrote the xlib driver, 8bpp X terminals were still 
pretty common.  For a while I was using a monochrome X terminal and 
Mesa was able to dither down to 1bpp!

Directly reading/writing spans to Ximages and Pixmaps was the fast way 
to do sw rendering once upon a time.


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