[Mesa-dev] [PATCH v2 18/23] i965: Implement GL_PRIMITIVES_GENERATED with non-zero streams.

[Chris Forbes]

It looks like you can have the SOL stage increment that counter even
when not doing any actual streamout, which should give you the correct
semantics.

See the definition of 3DSTATE_STREAMOUT in the Haswell PRM, Volume 2b. You want:

- dw1.31 SO Function Enable = 1
- dw1.25 SO Statistics Enable = 1
- dw1.8-11 SO Buffer Enable [n] = 0

This should behave just like having the unit disabled, except the
SO_PRIMITIVE_STORAGE_NEEDED registers will increment.

-- Chris


On Wed, Jun 18, 2014 at 9:51 PM, Iago Toral Quiroga <itoral at igalia.com> wrote:
> So far we have been using CL_INVOCATION_COUNT to resolve this query but this
> is no good with streams, as only stream 0 reaches the clipping stage.
>
> From ARB_transform_feedback3:
>
> "When a generated primitive query for a vertex stream is active, the
>  primitives-generated count is incremented every time a primitive emitted to
>  that stream reaches the Discarding Rasterization stage (see Section 3.x)
>  right before rasterization. This counter is incremented whether or not
>  transform feedback is active."
>
> Unfortunately, I don't see any registers that provide the number of primitives
> written to a specific stream other than the ones that track the number of
> primitives written to transform feedback in the SOL stage, so I think we can't
> implement this exactly as specified. This should not be a major issue though,
> since non-zero streams are pointless unless they are bound to transform feedback
> buffers anyway.
>
> Also in ARB_transform_feedback3:
>
> "These two types of queries can be used together to determine if all
>  primitives in a given vertex stream have been written to the bound
>  feedback buffers; if both queries are run simultaneously and the query
>  results are equal, all primitives have been written to the buffer(s).  If
>  the number of primitives written is less than the number of primitives
>  generated, one or more buffers overflowed.
>
> This refers to GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN and
> GL_PRIMITIVES_GENERATED. This behavior is achieved by implementing primitives
> generated queries through GEN7_SO_PRIM_STORAGE_NEEDED for non-zero streams.
> ---
>  src/mesa/drivers/dri/i965/gen6_queryobj.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/gen6_queryobj.c b/src/mesa/drivers/dri/i965/gen6_queryobj.c
> index 0cb64ca..ee33e1d 100644
> --- a/src/mesa/drivers/dri/i965/gen6_queryobj.c
> +++ b/src/mesa/drivers/dri/i965/gen6_queryobj.c
> @@ -84,11 +84,16 @@ brw_store_register_mem64(struct brw_context *brw,
>
>  static void
>  write_primitives_generated(struct brw_context *brw,
> -                           drm_intel_bo *query_bo, int idx)
> +                           drm_intel_bo *query_bo, int stream, int idx)
>  {
>     intel_batchbuffer_emit_mi_flush(brw);
>
> -   brw_store_register_mem64(brw, query_bo, CL_INVOCATION_COUNT, idx);
> +   if (brw->gen >= 7 && stream > 0) {
> +      brw_store_register_mem64(brw, query_bo,
> +                               GEN7_SO_PRIM_STORAGE_NEEDED(stream), idx);
> +   } else {
> +      brw_store_register_mem64(brw, query_bo, CL_INVOCATION_COUNT, idx);
> +   }
>  }
>
>  static void
> @@ -240,7 +245,7 @@ gen6_begin_query(struct gl_context *ctx, struct gl_query_object *q)
>        break;
>
>     case GL_PRIMITIVES_GENERATED:
> -      write_primitives_generated(brw, query->bo, 0);
> +      write_primitives_generated(brw, query->bo, query->Base.Stream, 0);
>        break;
>
>     case GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN:
> @@ -279,7 +284,7 @@ gen6_end_query(struct gl_context *ctx, struct gl_query_object *q)
>        break;
>
>     case GL_PRIMITIVES_GENERATED:
> -      write_primitives_generated(brw, query->bo, 1);
> +      write_primitives_generated(brw, query->bo, query->Base.Stream, 1);
>        break;
>
>     case GL_TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN:
> --
> 1.9.1
>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev