[Mesa-dev] [PATCH 2/3] swrast: Add a note about overlapping support for framebuffer blit.

[Brian Paul]

On Tue, Dec 13, 2011 at 1:53 PM, Eric Anholt <eric at anholt.net> wrote:
> ---
>  src/mesa/swrast/s_blit.c |   10 +++++++++-
>  1 files changed, 9 insertions(+), 1 deletions(-)
>
> diff --git a/src/mesa/swrast/s_blit.c b/src/mesa/swrast/s_blit.c
> index 2817ec1..803ad2e 100644
> --- a/src/mesa/swrast/s_blit.c
> +++ b/src/mesa/swrast/s_blit.c
> @@ -478,7 +478,15 @@ simple_blit(struct gl_context *ctx,
>    ASSERT(srcX1 - srcX0 == dstX1 - dstX0);
>    ASSERT(srcY1 - srcY0 == dstY1 - dstY0);
>
> -   /* determine if copy should be bottom-to-top or top-to-bottom */
> +   /* From the GL_ARB_framebuffer_object spec:
> +    *
> +    *     "If the source and destination buffers are identical, and the source
> +    *      and destination rectangles overlap, the result of the blit operation
> +    *      is undefined."
> +    *
> +    * However, we provide the expected result anyway by flipping the order of
> +    * the memcpy of rows.
> +    */
>    if (srcY0 > dstY0) {
>       /* src above dst: copy bottom-to-top */
>       yStep = 1;


Reviewed-by: Brian Paul <brianp at vmware.com>