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

[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.

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);
-- 
2.18.0