[Mesa-dev] meta: Disable dithering during glBlitFramebuffer

[Neil Roberts]

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
---
 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