[Mesa-dev] [PATCH 3/3 v2] i965/bdw: Fix 3DSTATE_VF_INSTANCING when the edge flag is used

[Neil Roberts]

When the edge flag element is enabled then the elements are slightly
reordered so that the edge flag is always the last one. This was
confusing the code to upload the 3DSTATE_VF_INSTANCING state because
that is uploaded with a separate loop which has an instruction for
each element. The indices used in these instructions weren't taking
into account the reordering so the state would be incorrect.

v2: Use nr_elements instead of brw->vb.nr_enabled so that it will cope
    when gl_VertexID is used.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91292
Cc: "10.6 10.5" <mesa-stable at lists.freedesktop.org>
---
 src/mesa/drivers/dri/i965/gen8_draw_upload.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/gen8_draw_upload.c b/src/mesa/drivers/dri/i965/gen8_draw_upload.c
index 2bac5ff..1b48643 100644
--- a/src/mesa/drivers/dri/i965/gen8_draw_upload.c
+++ b/src/mesa/drivers/dri/i965/gen8_draw_upload.c
@@ -246,13 +246,24 @@ gen8_emit_vertices(struct brw_context *brw)
    }
    ADVANCE_BATCH();
 
-   for (unsigned i = 0; i < brw->vb.nr_enabled; i++) {
+   for (unsigned i = 0, j = 0; i < brw->vb.nr_enabled; i++) {
       const struct brw_vertex_element *input = brw->vb.enabled[i];
       const struct brw_vertex_buffer *buffer = &brw->vb.buffers[input->buffer];
+      unsigned element_index;
+
+      /* The edge flag element is reordered to be the last one in the code
+       * above so we need to compensate for that in the element indices used
+       * below.
+       */
+      if (input == gen6_edgeflag_input)
+         element_index = nr_elements - 1;
+      else
+         element_index = j++;
 
       BEGIN_BATCH(3);
       OUT_BATCH(_3DSTATE_VF_INSTANCING << 16 | (3 - 2));
-      OUT_BATCH(i | (buffer->step_rate ? GEN8_VF_INSTANCING_ENABLE : 0));
+      OUT_BATCH(element_index |
+                (buffer->step_rate ? GEN8_VF_INSTANCING_ENABLE : 0));
       OUT_BATCH(buffer->step_rate);
       ADVANCE_BATCH();
    }
-- 
1.9.3