[PATCH 13/20] glamor: Add glamor_program based copy acceleration

[Markus Wick]

Am 2014-03-20 23:07, schrieb Keith Packard:
>>> +                    glCopyPixels (dx1 + dx - src_box->x1,
>>> +                                  dy1 + dy - src_box->y1,
>>> +                                  dx2 - dx1, dy2 - dy1, GL_COLOR);
>> 
>> This functions are deprecated fortunately. Please don't use them at 
>> all.
>> Glamor shall be used as hardware accelerated fallback, so we shouldn't
>> rely on uncommon features which may be implemented in software (eg on
>> nvidia) or not implemented at all (core, gles).
> 
> There isn't anything else I *can* use. GL doesn't otherwise define the
> results for operations using the same object for source and
> destination.

There isn't anything you can use. There is no point in using the 
deprecated function in an undefined way.
No GL copy function is defined for overlapping rects.
btw, you only check if the src and the dst are the same, you don't check 
for overlapping src+dst.


>> I guess GPUs have some special HW for this, but we can't use them on
>> OpenGL. memmove isn't parallelizable.
> 
> Yes, Intel GPUs have the 'blt' engine which performs overlapped copies
> correctly, and glCopyPixels is how we get to that. I imagine the same 
> is
> true for other GPUs.
> 
> As this operation is critical for many existing X applications for
> scrolling data around, we really have to make sure that we hit the
> special hardware.

But we can't know if the driver will use this hardware. Maybe with some 
special GL extension?
But also in this way, I'd suggest to use a modified glCopyImageSubData 
and/or glBlitFramebuffer to allow overlapping copys.