[Mesa-dev] [PATCH] glsl: Transform fb buffers are only active if a variable uses them

[Nicolai Hähnle]

On 06.11.2017 12:23, Neil Roberts wrote:
> The GL spec will soon be revised to clarify that a buffer binding for
> a transform feedback buffer is only required if a variable is actually
> defined to use the buffer binding point. Previously a declaration for
> the default transform buffer would make it require a binding even if
> nothing was declared to use the default buffer.
> 
> Affects:
> KHR-GL44/45.enhanced_layouts.xfb_stride_of_empty_list
> KHR-GL44/45.enhanced_layouts.xfb_stride_of_empty_list_and_api

Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>


> ---
>   src/compiler/glsl/link_varyings.cpp | 24 +++++++++++++++---------
>   1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
> index 66a20a2..e663930 100644
> --- a/src/compiler/glsl/link_varyings.cpp
> +++ b/src/compiler/glsl/link_varyings.cpp
> @@ -1364,7 +1364,6 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
>         if (has_xfb_qualifiers) {
>            for (unsigned j = 0; j < MAX_FEEDBACK_BUFFERS; j++) {
>               if (prog->TransformFeedback.BufferStride[j]) {
> -               buffers |= 1 << j;
>                  explicit_stride[j] = true;
>                  xfb_prog->sh.LinkedTransformFeedback->Buffers[j].Stride =
>                     prog->TransformFeedback.BufferStride[j] / 4;
> @@ -1389,10 +1388,24 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
>               num_buffers++;
>               buffer_stream_id = -1;
>               continue;
> -         } else if (tfeedback_decls[i].is_varying()) {
> +         }
> +
> +         if (has_xfb_qualifiers) {
> +            buffer = tfeedback_decls[i].get_buffer();
> +         } else {
> +            buffer = num_buffers;
> +         }
> +
> +         if (tfeedback_decls[i].is_varying()) {
>               if (buffer_stream_id == -1)  {
>                  /* First varying writing to this buffer: remember its stream */
>                  buffer_stream_id = (int) tfeedback_decls[i].get_stream_id();
> +
> +               /* Only mark a buffer as active when there is a varying
> +                * attached to it. This behaviour is based on a revised version
> +                * of section 13.2.2 of the GL 4.6 spec.
> +                */
> +               buffers |= 1 << buffer;
>               } else if (buffer_stream_id !=
>                          (int) tfeedback_decls[i].get_stream_id()) {
>                  /* Varying writes to the same buffer from a different stream */
> @@ -1408,13 +1421,6 @@ store_tfeedback_info(struct gl_context *ctx, struct gl_shader_program *prog,
>               }
>            }
>   
> -         if (has_xfb_qualifiers) {
> -            buffer = tfeedback_decls[i].get_buffer();
> -         } else {
> -            buffer = num_buffers;
> -         }
> -         buffers |= 1 << buffer;
> -
>            if (!tfeedback_decls[i].store(ctx, prog,
>                                          xfb_prog->sh.LinkedTransformFeedback,
>                                          buffer, num_buffers, num_outputs,
> 


-- 
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.