[Nouveau] [RFC] mesa/st: Avoid passing a NULL buffer to the drivers

[Ilia Mirkin]

Can you elaborate a bit as to why that's the right thing to do?

On Wed, Jan 7, 2015 at 1:52 PM, Tobias Klausmann
<tobias.johannes.klausmann at mni.thm.de> wrote:
> If we capture transform feedback from n stream in (n-1) buffers we face a
> NULL buffer, use the buffer (n-1) to capture the output of stream n.
>
> This fixes one piglit test with nvc0:
>    arb_gpu_shader5-xfb-streams-without-invocations
>
> Signed-off-by: Tobias Klausmann <tobias.johannes.klausmann at mni.thm.de>
> ---
>  src/mesa/state_tracker/st_cb_xformfb.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/src/mesa/state_tracker/st_cb_xformfb.c b/src/mesa/state_tracker/st_cb_xformfb.c
> index 8f75eda..5a12da4 100644
> --- a/src/mesa/state_tracker/st_cb_xformfb.c
> +++ b/src/mesa/state_tracker/st_cb_xformfb.c
> @@ -123,6 +123,11 @@ st_begin_transform_feedback(struct gl_context *ctx, GLenum mode,
>        struct st_buffer_object *bo = st_buffer_object(sobj->base.Buffers[i]);
>
>        if (bo) {
> +         if (!bo->buffer)
> +            /* If we capture transform feedback from n streams into (n-1)
> +             * buffers we have to write to buffer (n-1) for stream n.
> +             */
> +            bo = st_buffer_object(sobj->base.Buffers[i-1]);
>           /* Check whether we need to recreate the target. */
>           if (!sobj->targets[i] ||
>               sobj->targets[i] == sobj->draw_count ||
> --
> 2.2.1
>
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