> Unfortunately, I'm not able to find any comment about overlapping
> glCopyPixels at the OpenGL 1.2 spec (page 126, glCopyPixels
> Do you remember if overlapping glCopyPixels should be supported for all
> paths (for example, when convolution is enabled) ?
The closest that the spec comes to defining this is the order of operations
in describing it:
Values are obtained from the framebuffer, converted (if appropriate),
then subjected to the pixel transfer operations described in section 3.6.5,
just as if ReadPixels were called with the corresponding arguments. If the
type is STENCIL or DEPTH, then it is as if the format for ReadPixels were
STENCIL INDEX or DEPTH COMPONENT, respectively. If the type is COLOR, then if
the GL is in RGBA mode, it is as if the format were RGBA, while if the GL
is in color index mode, it is as if the format were COLOR INDEX.
The groups of elements so obtained are then written to the framebuffer
just as if DrawPixels had been given width and height, beginning with
final conversion of elements. The effective format is the same as that already
Because the spec says that the values are obtained "just as if ReadPixels were
later says "written ... just as if DrawPixels ...", I feel the only valid
is that the result must be as if read into main memory and then written. Thus,
when the rectangles overlap, the "values obtained" must be prior to the values
You can ask the ARB to clarify this, if you need an answer more authoritarian.
Andy V (OpenGL Alpha Geek)
"In order to make progress, one must leave the door to the unknown ajar."
Richard P. Feynman, quoted by Jagdish Mehra in _The Beat of a Different Drum_.
Paul Martz's OpenGL FAQ: http://www.opengl.org/developers/faqs/technical.html