[Mesa-dev] [PATCH 2/2] u_blitter: Add an option to draw the triangles using an index buffer.

[Roland Scheidegger]

Am 12.07.2018 um 00:05 schrieb Eric Anholt:
> For V3D, the HW will interpolate slightly differently along the shared
> edge of the trifan.  The conformance tests manage to catch this in the
> nearest_consistency_* group.  To get interpolation to match, we need the
> last vertex of the triangle to be shared.
> 
> I first tried implementing draw_rectangle to do triangles instead, but
> that was quite a bit (147 lines) of code duplication from u_blitter, and
> this seems much simpler and less likely to break as u_blitter changes.

I'm curious, how does interpolation work on that hw?
Does it use the provoking vertex as some sort of reference? If so would
it actually work if you switched to provoking vertex first (if you can)?
(But I'm really just curious, the patch looks alright to me.)

Roland


> 
> Fixes dEQP-GLES3.functional.fbo.blit.rect.nearest_consistency_* on V3D.
> ---
>  src/gallium/auxiliary/util/u_blitter.c | 16 ++++++++++++++--
>  src/gallium/auxiliary/util/u_blitter.h |  2 ++
>  src/gallium/drivers/v3d/v3d_context.c  |  1 +
>  3 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/src/gallium/auxiliary/util/u_blitter.c b/src/gallium/auxiliary/util/u_blitter.c
> index 4748627fc523..eadb76a109fb 100644
> --- a/src/gallium/auxiliary/util/u_blitter.c
> +++ b/src/gallium/auxiliary/util/u_blitter.c
> @@ -1258,8 +1258,20 @@ static void blitter_draw(struct blitter_context_priv *ctx,
>     pipe->set_vertex_buffers(pipe, ctx->base.vb_slot, 1, &vb);
>     pipe->bind_vertex_elements_state(pipe, vertex_elements_cso);
>     pipe->bind_vs_state(pipe, get_vs(&ctx->base));
> -   util_draw_arrays_instanced(pipe, PIPE_PRIM_TRIANGLE_FAN, 0, 4,
> -                              0, num_instances);
> +
> +   if (ctx->base.use_index_buffer) {
> +      /* Note that for V3D,
> +       * dEQP-GLES3.functional.fbo.blit.rect.nearest_consistency_* require
> +       * that the last vert of the two tris be the same.
> +       */
> +      static uint8_t indices[6] = { 0, 1, 2, 0, 3, 2 };
> +      util_draw_elements_instanced(pipe, indices, 1, 0,
> +                                   PIPE_PRIM_TRIANGLES, 0, 6,
> +                                   0, num_instances);
> +   } else {
> +      util_draw_arrays_instanced(pipe, PIPE_PRIM_TRIANGLE_FAN, 0, 4,
> +                                 0, num_instances);
> +   }
>     pipe_resource_reference(&vb.buffer.resource, NULL);
>  }
>  
> diff --git a/src/gallium/auxiliary/util/u_blitter.h b/src/gallium/auxiliary/util/u_blitter.h
> index 9e945983baac..9ea1dc9b6b28 100644
> --- a/src/gallium/auxiliary/util/u_blitter.h
> +++ b/src/gallium/auxiliary/util/u_blitter.h
> @@ -100,6 +100,8 @@ struct blitter_context
>     /* Whether the blitter is running. */
>     bool running;
>  
> +   bool use_index_buffer;
> +
>     /* Private members, really. */
>     struct pipe_context *pipe; /**< pipe context */
>  
> diff --git a/src/gallium/drivers/v3d/v3d_context.c b/src/gallium/drivers/v3d/v3d_context.c
> index cef32ceb069d..6fb807b1aa8a 100644
> --- a/src/gallium/drivers/v3d/v3d_context.c
> +++ b/src/gallium/drivers/v3d/v3d_context.c
> @@ -164,6 +164,7 @@ v3d_context_create(struct pipe_screen *pscreen, void *priv, unsigned flags)
>          v3d->blitter = util_blitter_create(pctx);
>          if (!v3d->blitter)
>                  goto fail;
> +        v3d->blitter->use_index_buffer = true;
>  
>          v3d->primconvert = util_primconvert_create(pctx,
>                                                     (1 << PIPE_PRIM_QUADS) - 1);
>