[Mesa-dev] [PATCH 2/2] vbo: Merge primitive drawing requests in display lists.

[Jordan Justen]

On Fri, Feb 1, 2013 at 1:34 PM, Eric Anholt <eric at anholt.net> wrote:
> minecraft apparently has its piles of display lists each contain 6
> instances of glBegin(GL_QUADS)/verts/glEnd(), which appear in the
> compiled list as 6 prims of 4 verts each in one draw call.  We can
> reduce driver overhead even more by making that one prim of 24 verts.
>
> Improves minecraft performance by 1.6% +/- .25% (n=446)
> ---
>  src/mesa/vbo/vbo_save_api.c |   43 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 43 insertions(+)
>
> diff --git a/src/mesa/vbo/vbo_save_api.c b/src/mesa/vbo/vbo_save_api.c
> index 789e864..7490717 100644
> --- a/src/mesa/vbo/vbo_save_api.c
> +++ b/src/mesa/vbo/vbo_save_api.c
> @@ -301,6 +301,47 @@ _save_reset_counters(struct gl_context *ctx)
>     save->dangling_attr_ref = 0;
>  }
>
> +/**
> + * For a list of prims, try merging prims that can just be extensions of the
> + * previous prim.
> + */
> +static void
> +vbo_merge_prims(struct gl_context *ctx,
> +                struct _mesa_prim *prim_list,
> +                GLuint *prim_count)
> +{
> +   GLuint i;
> +   struct _mesa_prim *prev_prim = prim_list;
> +
> +   for (i = 1; i < *prim_count; i++) {
> +      struct _mesa_prim *this_prim = prim_list + i;
> +
> +      if (this_prim->mode == prev_prim->mode &&
> +          this_prim->mode == GL_QUADS &&
> +          this_prim->count % 4 == 0 &&
> +          prev_prim->count % 4 == 0 &&

It seems like you might be able cover GL_POINTS, GL_LINES and
GL_TRIANGLES fairly easily too.

Reviewed-by: Jordan Justen <jordan.l.justen at intel.com>

> +          this_prim->start == prev_prim->start + prev_prim->count &&
> +          this_prim->basevertex == prev_prim->basevertex &&
> +          this_prim->num_instances == prev_prim->num_instances &&
> +          this_prim->base_instance == prev_prim->base_instance) {
> +         /* We've found a prim that just extend the previous one.  Tack it
> +          * onto the previous one, and let this primitive struct get dropped.
> +          */
> +         prev_prim->count += this_prim->count;
> +         prev_prim->end = this_prim->end;
> +         continue;
> +      }
> +
> +      /* If any previous primitives have been dropped, then we need to copy
> +       * this later one into the next available slot.
> +       */
> +      prev_prim++;
> +      if (prev_prim != this_prim)
> +         *prev_prim = *this_prim;
> +   }
> +
> +   *prim_count = prev_prim - prim_list + 1;
> +}
>
>  /**
>   * Insert the active immediate struct onto the display list currently
> @@ -380,6 +421,8 @@ _save_compile_vertex_list(struct gl_context *ctx)
>      */
>     save->copied.nr = _save_copy_vertices(ctx, node, save->buffer);
>
> +   vbo_merge_prims(ctx, node->prim, &node->prim_count);
> +
>     /* Deal with GL_COMPILE_AND_EXECUTE:
>      */
>     if (ctx->ExecuteFlag) {
> --
> 1.7.10.4
>
> _______________________________________________
> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/mesa-dev