[Mesa-dev] meta: Disable dithering during glBlitFramebuffer

[Pohjolainen, Topi]

On Mon, Aug 04, 2014 at 09:03:23PM +0100, Neil Roberts wrote:
> According to the GL spec the only fragment operations that should affect
> glBlitFramebuffer are ???the pixel ownership test, the scissor test, and sRGB
> conversion???. That implies that dithering should not be performed so we need to
> disable it when implementing the blit with a render.
> 
> Before commit 05b52efbc97731 the dithering state would be left as whatever the
> application picks (the default being GL_TRUE) and after that commit it was
> explicitly enabled. Neither of these were correct.
> 
> https://bugs.freedesktop.org/show_bug.cgi?id=81828

This makes sense to me also, and more importantly fixes the bug:

Reviewed-by: Topi Pohjolainen <topi.pohjolainen at intel.com>

> ---
>  src/mesa/drivers/common/meta_blit.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/src/mesa/drivers/common/meta_blit.c b/src/mesa/drivers/common/meta_blit.c
> index bbf0c3c..b28b9d0 100644
> --- a/src/mesa/drivers/common/meta_blit.c
> +++ b/src/mesa/drivers/common/meta_blit.c
> @@ -709,6 +709,9 @@ _mesa_meta_BlitFramebuffer(struct gl_context *ctx,
>      */
>     _mesa_meta_begin(ctx, MESA_META_ALL & ~MESA_META_DRAW_BUFFERS);
>  
> +   /* Dithering shouldn't be performed for glBlitFramebuffer */
> +   _mesa_set_enable(ctx, GL_DITHER, GL_FALSE);
> +
>     /* If the clipping earlier changed the destination rect at all, then
>      * enable the scissor to clip to it.
>      */
> -- 
> 1.9.3
>