mesa: Generate correct error code in glDrawBuffers()

OpenGL 3.3 spec expects GL_INVALID_OPERATION:
 "For both the default framebuffer and framebuffer objects, the
  constants FRONT, BACK, LEFT, RIGHT, and FRONT AND BACK are not
  valid in the bufs array passed to DrawBuffers, and will result
  in the error INVALID OPERATION."

But OpenGL 4.0 spec changed the error code to GL_INVALID_ENUM:
 "For both the default framebuffer and framebuffer objects, the
  constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK are not
  valid in the bufs array passed to DrawBuffers, and will result
  in the error INVALID_ENUM."

This patch changes the behaviour to match OpenGL 4.0 spec
Fixes Khronos OpenGL CTS draw_buffers_api.test.

V2: Update the comment in code.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
(cherry picked from commit 33034755583edfb7c5b773b8e38a9dfa8d317821)

1 files changed, 5 insertions, 3 deletions

diff --git a/src/mesa/main/buffers.c b/src/mesa/main/buffers.c
index 2bdbf41be5d..6cbce9d5da2 100644
--- a/src/mesa/main/buffers.c
+++ b/src/mesa/main/buffers.c
@@ -360,16 +360,18 @@ _mesa_DrawBuffers(GLsizei n, const GLenum *buffers)
             return;
          }         
 
-         /* From the OpenGL 3.0 specification, page 259:
+         /* From the OpenGL 4.0 specification, page 256:
           * "For both the default framebuffer and framebuffer objects, the
           *  constants FRONT, BACK, LEFT, RIGHT, and FRONT_AND_BACK are not
           *  valid in the bufs array passed to DrawBuffers, and will result in
-          *  the error INVALID_OPERATION.  This restriction is because these
+          *  the error INVALID_ENUM. This restriction is because these
           *  constants may themselves refer to multiple buffers, as shown in
           *  table 4.4."
+          *  Previous versions of the OpenGL specification say INVALID_OPERATION,
+          *  but the Khronos conformance tests expect INVALID_ENUM.
           */
          if (_mesa_bitcount(destMask[output]) > 1) {
-            _mesa_error(ctx, GL_INVALID_OPERATION, "glDrawBuffersARB(buffer)");
+            _mesa_error(ctx, GL_INVALID_ENUM, "glDrawBuffersARB(buffer)");
             return;
          }