[Mesa-dev] [PATCH 2/2] mesa/blit: Don't require the same format for mulitisample blits

[Neil Roberts]

Previously the GL spec required that whenever glBlitFramebuffer is
used with either buffer being multisampled, the internal formats must
match. However the GL 4.4 spec was later changed to remove this
restriction. In the section entitled “Changes in the released
Specification of July 22, 2013” it says:

“Relax BlitFramebuffer in section 18.3.1 so that format conversion can
 take place during multisample blits, since drivers already allow this
 and some apps depend on it.”

If most drivers already allowed this in earlier versions I think it's
safe to assume that this is a spec bug and it should also be allowed
in all versions.

This patch just removes the restriction on desktop GL. For GLES there
are conformance tests that assert the previous behaviour so it is
probably safer to leave it in.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92706
---

There is a corresponding update to Piglit to make it expect this new
behaviour here:

http://patchwork.freedesktop.org/patch/63670/

I've only tested this with SKL and HSW. It passed fine on SKL but it
needs the previous patch to work on HSW. I put it through a full
Jenkins run but it doesn't really test much without the Piglit patch
as well and I don't think I can post Piglit patches to Jenkins.

As this enables the new behaviour for all Mesa drivers of course it
would need some testing with other drivers before landing.

 src/mesa/main/blit.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/mesa/main/blit.c b/src/mesa/main/blit.c
index a32f1a4..6803062 100644
--- a/src/mesa/main/blit.c
+++ b/src/mesa/main/blit.c
@@ -285,7 +285,8 @@ _mesa_blit_framebuffer(struct gl_context *ctx,
             /* extra checks for multisample copies... */
             if (readFb->Visual.samples > 0 || drawFb->Visual.samples > 0) {
                /* color formats must match */
-               if (!compatible_resolve_formats(colorReadRb, colorDrawRb)) {
+               if (_mesa_is_gles(ctx) &&
+                   !compatible_resolve_formats(colorReadRb, colorDrawRb)) {
                   _mesa_error(ctx, GL_INVALID_OPERATION,
                          "%s(bad src/dst multisample pixel formats)", func);
                   return;
-- 
1.9.3