draw/clip: fix viewport index for geometry shaders

The old code updated the viewport index on the first vertex in
a primitive, however it was picking the first vertex wrong
when used with geometry shaders.

This code has access to the prim info with the primitive lengths
so instead keep track of when a new primitive starts by tracking
the lengths and updating the viewport index then. The prim info
is only valid after a GS or prim assembly, so enable prim assembly
if a vertex shader ever uses viewport index.

This fixes:
piglit arb_viewport_array-render-viewport-2
KHR-GLES31.core.viewport_array.draw_to_single_layer_with_multiple_viewports,Fail
KHR-GLES31.core.viewport_array.draw_mulitple_viewports_with_single_invocation,Fail
KHR-GLES31.core.viewport_array.draw_multiple_layers,Fail
KHR-GLES31.core.viewport_array.depth_range,Fail

Reviewed-by: Roland Scheidegger <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5489>

2 files changed, 8 insertions, 2 deletions

diff --git a/src/gallium/auxiliary/draw/draw_cliptest_tmp.h b/src/gallium/auxiliary/draw/draw_cliptest_tmp.h
index ba02461db48..b7c77bfd85d 100644
--- a/src/gallium/auxiliary/draw/draw_cliptest_tmp.h
+++ b/src/gallium/auxiliary/draw/draw_cliptest_tmp.h
@@ -49,7 +49,6 @@ static boolean TAG(do_cliptest)( struct pt_post_vs *pvs,
    int viewport_index = 0;
    int num_written_clipdistance =
       draw_current_shader_num_written_clipdistances(pvs->draw);
-   unsigned verts_per_prim = u_vertices_per_prim(prim_info->prim);
 
    if (uses_vp_idx) {
       viewport_index = u_bitcast_f2u(out->data[viewport_index_output][0]);
@@ -70,16 +69,20 @@ static boolean TAG(do_cliptest)( struct pt_post_vs *pvs,
    }
 
    assert(pos != -1);
+   unsigned prim_idx = 0, prim_vert_idx = 0;
    for (j = 0; j < info->count; j++) {
       float *position = out->data[pos];
       unsigned mask = 0x0;
 
       if (uses_vp_idx) {
          /* only change the viewport_index for the leading vertex */
-         if (!(j % verts_per_prim)) {
+         if (prim_vert_idx == (prim_info->primitive_lengths[prim_idx])) {
+            prim_idx++;
+            prim_vert_idx = 0;
             viewport_index = u_bitcast_f2u(out->data[viewport_index_output][0]);
             viewport_index = draw_clamp_viewport_idx(viewport_index);
          }
+         prim_vert_idx++;
       }
       float *scale = pvs->draw->viewports[viewport_index].scale;
       float *trans = pvs->draw->viewports[viewport_index].translate;
diff --git a/src/gallium/auxiliary/draw/draw_prim_assembler.c b/src/gallium/auxiliary/draw/draw_prim_assembler.c
index c0bc145f38b..edaaf0d501f 100644
--- a/src/gallium/auxiliary/draw/draw_prim_assembler.c
+++ b/src/gallium/auxiliary/draw/draw_prim_assembler.c
@@ -76,6 +76,9 @@ draw_prim_assembler_is_required(const struct draw_context *draw,
                                 const struct draw_prim_info *prim_info,
                                 const struct draw_vertex_info *vert_info)
 {
+   /* viewport index requires primitive boundaries to get correct vertex */
+   if (draw_current_shader_uses_viewport_index(draw))
+      return TRUE;
    switch (prim_info->prim) {
    case PIPE_PRIM_LINES_ADJACENCY:
    case PIPE_PRIM_LINE_STRIP_ADJACENCY: