[Mesa-dev] [PATCH] mesa: fix spurious wglGetProcAddress / GL_INVALID_OPERATION error

[Brian Paul]

On Windows, the Piglit primitive-restart test was failing a
glGetError()==0 assertion when it was run w/out any command line
arguments.  Piglit's all.py script only runs primitive-restart
with arguments so this case isn't normally hit during a full
piglit run.

The basic problem is Microsoft's opengl32.dll calls glFlush
from wglGetProcAddress() and Piglit uses wglGetProcAddress() to
resolve glPrimitiveRestartNV() which is called inside glBegin/End.
See comments in the code for more info.

Plus, improve the comments for _mesa_alloc_dispatch_table().

Cc: <mesa-stable at lists.freedesktop.org>
---
 src/mesa/main/context.c |   36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/mesa/main/context.c b/src/mesa/main/context.c
index afe43a6..5a8f718 100644
--- a/src/mesa/main/context.c
+++ b/src/mesa/main/context.c
@@ -891,7 +891,21 @@ _mesa_generic_nop(void)
 
 
 /**
- * Allocate and initialize a new dispatch table.
+ * Special no-op glFlush, see below.
+ */
+#if defined(_WIN32)
+static void GLAPIENTRY
+nop_glFlush(void)
+{
+   /* don't record an error like we do in _mesa_generic_nop() */
+}
+#endif
+
+
+/**
+ * Allocate and initialize a new dispatch table.  All the dispatch
+ * function pointers will point at the _mesa_generic_nop() function
+ * which raises GL_INVALID_OPERATION.
  */
 struct _glapi_table *
 _mesa_alloc_dispatch_table(void)
@@ -911,6 +925,26 @@ _mesa_alloc_dispatch_table(void)
       for (i = 0; i < numEntries; i++) {
          entry[i] = (_glapi_proc) _mesa_generic_nop;
       }
+
+#if defined(_WIN32)
+      /* This is a special case for Windows in the event that
+       * wglGetProcAddress is called between glBegin/End().
+       *
+       * The MS opengl32.dll library apparently calls glFlush from
+       * wglGetProcAddress().  If we're inside glBegin/End(), glFlush
+       * will dispatch to _mesa_generic_nop() and we'll generate a
+       * GL_INVALID_OPERATION error.
+       *
+       * The specific case which hits this is piglit's primitive-restart
+       * test which calls glPrimitiveRestartNV() inside glBegin/End.  The
+       * first time we call glPrimitiveRestartNV() Piglit's API dispatch
+       * code will try to resolve the function by calling wglGetProcAddress.
+       * This raises GL_INVALID_OPERATION and an assert(glGetError()==0)
+       * will fail causing the test to fail.  By suppressing the error, the
+       * assertion passes and the test continues.
+       */
+      SET_Flush(table, nop_glFlush);
+#endif
    }
    return table;
 }
-- 
1.7.10.4