[Mesa-dev] [PATCH] mesa: Correctly use glDrawBuffers for multiple buffers and glDrawBuffer for one buffer.

[Popov, Pavel E]

Hi Kenneth, Ian,

Could you look through my patch?

Regards,
Pavel

-----Original Message-----
From: Popov, Pavel E 
Sent: Thursday, July 17, 2014 10:21 PM
To: mesa-dev at lists.freedesktop.org
Cc: Popov, Pavel E
Subject: [PATCH] mesa: Correctly use glDrawBuffers for multiple buffers and glDrawBuffer for one buffer.

According to spec (OpenGL 4.0 specification, pages 254-255) we have a different bits set for one buffer and for multiple buffers. For glDrawBuffer we may have up to four bits set but for glDrawBuffers we can only have one bit set.

The _mesa_drawbuffers is called with ctx->Const.MaxDrawBuffers and NULL arguments when _mesa_update_framebuffer or _mesa_update_draw_buffers is called. In this situation realization for glDrawBuffers is used for any number of buffers. Even for one. But glDrawBuffer have to be used for one buffer instead of glDrawBuffers.

Piglit test 'gl30basic' fails with assert with debug Mesa and pass with release
    'main/buffers.c:520: _mesa_drawbuffers: Assertion `__builtin_popcount(destMask[buf]) == 1' failed.'
Probably some other tests also can be affected.

Signed-off-by: Pavel Popov <pavel.e.popov at intel.com>
---
 src/mesa/main/buffers.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/mesa/main/buffers.c b/src/mesa/main/buffers.c index b13a7af..a640360 100644
--- a/src/mesa/main/buffers.c
+++ b/src/mesa/main/buffers.c
@@ -480,6 +480,7 @@ _mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
    struct gl_framebuffer *fb = ctx->DrawBuffer;
    GLbitfield mask[MAX_DRAW_BUFFERS];
    GLuint buf;
+   GLuint m = n;
 
    if (!destMask) {
       /* compute destMask values now */ @@ -489,15 +490,17 @@ _mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
          mask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
          ASSERT(mask[output] != BAD_MASK);
          mask[output] &= supportedMask;
+         if (mask[output] == 0)
+            m--;
       }
       destMask = mask;
    }
 
    /*
-    * If n==1, destMask[0] may have up to four bits set.
+    * If m==1, destMask[0] may have up to four bits set.
     * Otherwise, destMask[x] can only have one bit set.
     */
-   if (n == 1) {
+   if (m == 1) {
       GLuint count = 0, destMask0 = destMask[0];
       while (destMask0) {
          GLint bufIndex = ffs(destMask0) - 1;
--
1.9.1


--------------------------------------------------------------------
Closed Joint Stock Company Intel A/O
Registered legal address: Krylatsky Hills Business Park, 
17 Krylatskaya Str., Bldg 4, Moscow 121614, 
Russian Federation

This e-mail and any attachments may contain confidential material for
the sole use of the intended recipient(s). Any review or distribution
by others is strictly prohibited. If you are not the intended
recipient, please contact the sender and delete all copies.