st/mesa: add a fallback for clear_with_quad when no vs_layer

Not all drivers can set gl_Layer from VS. Add a fallback that passes the
instance id from VS to GS, and then uses the GS to set the layer.

Tested by adding

  quad_buffers |= clear_buffers;
  clear_buffers = 0;

to the st_Clear logic, and forcing set_vertex_shader_layered in all
cases. No piglit regressions (on piglits with 'clear' in the name).

Signed-off-by: Ilia Mirkin <[email protected]>
Reviewed-by: Marek Olšák <[email protected]>
Cc: "10.4 10.3" <[email protected]>

2 files changed, 21 insertions, 5 deletions

diff --git a/src/mesa/state_tracker/st_cb_clear.c b/src/mesa/state_tracker/st_cb_clear.c
index 3a359f31885..45dea594ee7 100644
--- a/src/mesa/state_tracker/st_cb_clear.c
+++ b/src/mesa/state_tracker/st_cb_clear.c
@@ -88,6 +88,14 @@ st_destroy_clear(struct st_context *st)
       cso_delete_vertex_shader(st->cso_context, st->clear.vs);
       st->clear.vs = NULL;
    }
+   if (st->clear.vs_layered) {
+      cso_delete_vertex_shader(st->cso_context, st->clear.vs_layered);
+      st->clear.vs_layered = NULL;
+   }
+   if (st->clear.gs_layered) {
+      cso_delete_geometry_shader(st->cso_context, st->clear.gs_layered);
+      st->clear.gs_layered = NULL;
+   }
 }
 
 
@@ -128,6 +136,7 @@ set_vertex_shader(struct st_context *st)
    }
 
    cso_set_vertex_shader_handle(st->cso_context, st->clear.vs);
+   cso_set_geometry_shader_handle(st->cso_context, NULL);
 }
 
 
@@ -136,18 +145,25 @@ set_vertex_shader_layered(struct st_context *st)
 {
    struct pipe_context *pipe = st->pipe;
 
-   if (!pipe->screen->get_param(pipe->screen, PIPE_CAP_TGSI_INSTANCEID) ||
-       !pipe->screen->get_param(pipe->screen, PIPE_CAP_TGSI_VS_LAYER_VIEWPORT)) {
-      assert(!"Got layered clear, but the VS layer output is unsupported");
+   if (!pipe->screen->get_param(pipe->screen, PIPE_CAP_TGSI_INSTANCEID)) {
+      assert(!"Got layered clear, but VS instancing is unsupported");
       set_vertex_shader(st);
       return;
    }
 
    if (!st->clear.vs_layered) {
-      st->clear.vs_layered = util_make_layered_clear_vertex_shader(pipe);
+      bool vs_layer =
+         pipe->screen->get_param(pipe->screen, PIPE_CAP_TGSI_VS_LAYER_VIEWPORT);
+      if (vs_layer) {
+         st->clear.vs_layered = util_make_layered_clear_vertex_shader(pipe);
+      } else {
+         st->clear.vs_layered = util_make_layered_clear_helper_vertex_shader(pipe);
+         st->clear.gs_layered = util_make_layered_clear_geometry_shader(pipe);
+      }
    }
 
    cso_set_vertex_shader_handle(st->cso_context, st->clear.vs_layered);
+   cso_set_geometry_shader_handle(st->cso_context, st->clear.gs_layered);
 }
 
 
@@ -331,7 +347,6 @@ clear_with_quad(struct gl_context *ctx, unsigned clear_buffers)
    }
 
    set_fragment_shader(st);
-   cso_set_geometry_shader_handle(st->cso_context, NULL);
 
    if (num_layers > 1)
       set_vertex_shader_layered(st);
diff --git a/src/mesa/state_tracker/st_context.h b/src/mesa/state_tracker/st_context.h
index 58f14f954dc..15f9df492db 100644
--- a/src/mesa/state_tracker/st_context.h
+++ b/src/mesa/state_tracker/st_context.h
@@ -181,6 +181,7 @@ struct st_context
       void *vs;
       void *fs;
       void *vs_layered;
+      void *gs_layered;
    } clear;
 
    /** used for anything using util_draw_vertex_buffer */