st/mesa: don't set 16 scissors and 16 viewports if they're unused

Only do so if there is a shader writing gl_ViewportIndex.
This removes a lot of CPU overhead for the most common case.

Reviewed-by: Nicolai Hähnle <[email protected]>

1 files changed, 18 insertions, 0 deletions

diff --git a/src/mesa/state_tracker/st_atom.c b/src/mesa/state_tracker/st_atom.c
index bcfbcf878f0..253b5081640 100644
--- a/src/mesa/state_tracker/st_atom.c
+++ b/src/mesa/state_tracker/st_atom.c
@@ -76,6 +76,7 @@ static void check_program_state( struct st_context *st )
    struct gl_program *new_gp = ctx->GeometryProgram._Current;
    struct gl_program *new_fp = ctx->FragmentProgram._Current;
    uint64_t dirty = 0;
+   unsigned num_viewports = 1;
 
    /* Flag states used by both new and old shaders to unbind shader resources
     * properly when transitioning to shaders that don't use them.
@@ -115,6 +116,23 @@ static void check_program_state( struct st_context *st )
          dirty |= st_fragment_program(new_fp)->affected_states;
    }
 
+   /* Find out the number of viewports. This determines how many scissors
+    * and viewport states we need to update.
+    */
+   struct gl_program *last_prim_shader = new_gp ? new_gp :
+                                         new_tep ? new_tep : new_vp;
+   if (last_prim_shader &&
+       last_prim_shader->info.outputs_written & VARYING_BIT_VIEWPORT)
+      num_viewports = ctx->Const.MaxViewports;
+
+   if (st->state.num_viewports != num_viewports) {
+      st->state.num_viewports = num_viewports;
+      dirty |= ST_NEW_VIEWPORT;
+
+      if (ctx->Scissor.EnableFlags & u_bit_consecutive(0, num_viewports))
+         dirty |= ST_NEW_SCISSOR;
+   }
+
    st->dirty |= dirty;
 }