mesa: Add dd_function_table::PrepareExecBegin

This hook allows the driver to prepare for a glBegin/glEnd.

i965 will use the hook to avoid avoid recursive calls to FLUSH_VERTICES
during a buffer resolve meta-op.

Detailed Justification
----------------------
When vertices are queued during a glBegin/glEnd block, those vertices must
of course be drawn before any rendering state changes. To enusure this,
Mesa calls FLUSH_VERTICES as a prehook to such state changes. Therefore,
FLUSH_VERTICES itself cannot change rendering state without falling into
a recursive trap.

This precludes meta-ops, namely i965 buffer resolves, from occuring while
any vertices are queued. To avoid that situation, i965 must satisfy the
following condition: that it queues no vertex if a buffer needs resolving.
To satisfy this, i965 will use the PrepareExecBegin hook to resolve all
buffers on entering a glBegin/glEnd block.

--------
v2: Don't add dd_function_table::CleanupExecEnd. Anholt and I discovered
    that hook to be unnecessary.

Reviewed-by: Brian Paul <[email protected]>
Signed-off-by: Chad Versace <[email protected]>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/mesa/main/dd.h b/src/mesa/main/dd.h
index 4e017ae3843..8607008dee6 100644
--- a/src/mesa/main/dd.h
+++ b/src/mesa/main/dd.h
@@ -861,6 +861,14 @@ struct dd_function_table {
    void (*SaveFlushVertices)( struct gl_context *ctx );
 
    /**
+    * \brief Hook for drivers to prepare for a glBegin/glEnd block
+    *
+    * This hook is called in vbo_exec_Begin() before any action, including
+    * state updates, occurs.
+    */
+   void (*PrepareExecBegin)( struct gl_context *ctx );
+
+   /**
     * Give the driver the opportunity to hook in its own vtxfmt for
     * compiling optimized display lists.  This is called on each valid
     * glBegin() during list compilation.