On Sun, Mar 14, 2010 at 10:28 AM, Chia-I Wu <olva...@gmail.com> wrote:
> On Sun, Mar 14, 2010 at 4:53 PM, Keith Whitwell
> <keith.whitw...@googlemail.com> wrote:
>> This looks like it introduces an extra full-window copying operation
>> at every swapbuffers... is that correct?
>> If so, I think we should try to figure out an alternative approach
>> without the copying... would actually flipping between two textures
>> (thus preserving the old back/new front) contents be workable?
> Buffers swapping is handled in xmesa_swap_st_framebuffer. It is a zero-copy
> operation.
>
> This commit is to fix a bug when this code path is hit
>
> /* draw something and ... */
> glXSwapBuffers();
> glReadBuffer(GL_FRONT);
> glReadPixels();
>
> In the above, glReadBuffer will cause BUFFER_FRONT_LEFT renderbuffer to be
> added on demand as can be seen in st_ReadBuffer. The validation list would
> become { ST_ATTACHMENT_FRONT_LEFT, ST_ATTACHMENT_BACK_LEFT }. When
> glReadPixels is called, st/mesa will validate with the list and read from the
> front buffer.
>
> On the st/glx side, this use pattern is catched. When the front buffer is
> allocated, the contents of the back buffer will be copied to the front buffer.
> This happens only once. When the same code is run again, glXSwapBuffers will
> swap the buffers.
>
> The copying is required because xmesa_swap_st_framebuffer does not always swap
> the buffers. It is so that only the back buffer is allocated when the
> application never draws/reads the front buffer.
>
> --
> o...@lunarg.com
>
OK, sorry for being slow & thanks for explaining...
Keith
------------------------------------------------------------------------------
Download Intel® Parallel Studio Eval
Try the new software tools for yourself. Speed compiling, find bugs
proactively, and fine-tune applications for parallel performance.
See why Intel Parallel Studio got high marks during beta.
http://p.sf.net/sfu/intel-sw-dev
_______________________________________________
Mesa3d-dev mailing list
Mesa3d-dev@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/mesa3d-dev
