gallium: add start_slot parameter to set_vertex_buffers

This allows updating only a subrange of buffer bindings.

set_vertex_buffers(pipe, start_slot, count, NULL) unbinds buffers in that
range. Binding NULL resources unbinds buffers too (both buffer and user_buffer
must be NULL).

The meta ops are adapted to only save, change, and restore the single slot
they use. The cso_context can save and restore only one vertex buffer slot.
The clients can query which one it is using cso_get_aux_vertex_buffer_slot.
It's currently set to 0. (the Draw module breaks if it's set to non-zero)

It should decrease the CPU overhead when using a lot of meta ops, but
the drivers must be able to treat each vertex buffer slot as a separate
state (only r600g does so at the moment).

I can imagine this also being useful for optimizing some OpenGL use cases.

Reviewed-by: Brian Paul <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/mesa/state_tracker/st_context.c b/src/mesa/state_tracker/st_context.c
index da361d88795..69bd50336ec 100644
--- a/src/mesa/state_tracker/st_context.c
+++ b/src/mesa/state_tracker/st_context.c
@@ -173,7 +173,8 @@ st_create_context_priv( struct gl_context *ctx, struct pipe_context *pipe,
       memset(&st->velems_util_draw[i], 0, sizeof(struct pipe_vertex_element));
       st->velems_util_draw[i].src_offset = i * 4 * sizeof(float);
       st->velems_util_draw[i].instance_divisor = 0;
-      st->velems_util_draw[i].vertex_buffer_index = 0;
+      st->velems_util_draw[i].vertex_buffer_index =
+            cso_get_aux_vertex_buffer_slot(st->cso_context);
       st->velems_util_draw[i].src_format = PIPE_FORMAT_R32G32B32A32_FLOAT;
    }