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 <nicolai.haehnle@amd.com>

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;
 }
 

src/mesa/state_tracker/st_atom_scissor.c

@@ -53,7 +53,7 @@ st_update_scissor( struct st_context *st )
    unsigned i;
    bool changed = false;
 
-   for (i = 0 ; i < ctx->Const.MaxViewports; i++) {
+   for (i = 0 ; i < st->state.num_viewports; i++) {
       scissor[i].minx = 0;
       scissor[i].miny = 0;
       scissor[i].maxx = fb_width;
@@ -95,8 +95,12 @@ st_update_scissor( struct st_context *st )
          changed = true;
       }
    }
-   if (changed)
-      st->pipe->set_scissor_states(st->pipe, 0, ctx->Const.MaxViewports, scissor); /* activate */
+
+   if (changed) {
+      struct pipe_context *pipe = st->pipe;
+
+      pipe->set_scissor_states(pipe, 0, st->state.num_viewports, scissor);
+   }
 }
 
 void

src/mesa/state_tracker/st_atom_viewport.c

@@ -47,7 +47,7 @@ st_update_viewport( struct st_context *st )
 
    /* _NEW_VIEWPORT 
     */
-   for (i = 0; i < ctx->Const.MaxViewports; i++) {
+   for (i = 0; i < st->state.num_viewports; i++) {
       float *scale = st->state.viewport[i].scale;
       float *translate = st->state.viewport[i].translate;
 
@@ -62,6 +62,11 @@ st_update_viewport( struct st_context *st )
    }
 
    cso_set_viewport(st->cso_context, &st->state.viewport[0]);
-   if (ctx->Const.MaxViewports > 1)
-      st->pipe->set_viewport_states(st->pipe, 1, ctx->Const.MaxViewports - 1, &st->state.viewport[1]);
+
+   if (st->state.num_viewports > 1) {
+      struct pipe_context *pipe = st->pipe;
+
+      pipe->set_viewport_states(pipe, 1, st->state.num_viewports - 1,
+                                &st->state.viewport[1]);
+   }
 }

src/mesa/state_tracker/st_context.h

@@ -149,6 +149,7 @@ struct st_context
       unsigned fb_height;
       unsigned fb_num_samples;
       unsigned fb_num_layers;
+      unsigned num_viewports;
       struct pipe_scissor_state scissor[PIPE_MAX_VIEWPORTS];
       struct pipe_viewport_state viewport[PIPE_MAX_VIEWPORTS];
       struct {