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, 1 insertions, 0 deletions

diff --git a/src/mesa/drivers/common/driverfuncs.c b/src/mesa/drivers/common/driverfuncs.c
index 33da9346caf..263d4025ff3 100644
--- a/src/mesa/drivers/common/driverfuncs.c
+++ b/src/mesa/drivers/common/driverfuncs.c
@@ -208,6 +208,7 @@ _mesa_init_driver_functions(struct dd_function_table *driver)
    driver->ProgramStringNotify = _tnl_program_string;
    driver->FlushVertices = NULL;
    driver->SaveFlushVertices = NULL;
+   driver->PrepareExecBegin = NULL;
    driver->NotifySaveBegin = NULL;
    driver->LightingSpaceChange = NULL;