[Mesa3d-dev] [PATCH] Add language about implicit flush and command completion

[Ian Romanick]

On Sat, Jan 10, 2009 at 12:37:18PM +0100, Michel Dänzer wrote:
> On Fri, 2009-01-09 at 18:32 -0800, Ian Romanick wrote:
> > Copied language from the glXSwapBuffers manual page about the implicit
> > glFlush and expected command completion.  This just codifies what
> > people already expect from glXCopySubBufferMESA.  The intention of
> > this command is to work like glXSwapBuffers but on a sub-rectangle of
> > the drawable.
> 
> [...]
> 
> > +    glXCopySubBufferMESA performs an implicit glFlush before it
> > +    returns.  Subsequent OpenGL commands may be issued immediately
> > +    after calling glXCopySubBufferMESA, but are not executed until the
> > +    copy is completed. 
> 
> Note that the GLX spec is a little more complicated wrt this, it says:
> 
>         If dpy and draw are the display and drawable for the calling
>         thread’s current context, glXSwapBuffers performs an implicit
>         glFlush.
> 
> (I think the Mesa glXSwapBuffers code doesn't currently conform to this
> but unconditionally performs the implicit glFlush)

I think that's okay.  The extra flush is still conformant.  After all,
the driver can flush whenever it pleases.  The only requirement is
that the flush happen when the above conditions are met.  We certainly
do that.

I think the point you were trying to make, though, was that the
GLX_MESA_copy_sub_buffer spec should say something similar.  I agree.
I'll update the spec and post a new patch.
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