gpu: Add ARB_occlusion_query support.

cc/output/gl_renderer.cc

Index: cc/output/gl_renderer.cc
diff --git a/cc/output/gl_renderer.cc b/cc/output/gl_renderer.cc
index 2ef2d36ba4252b5e864e25c652a5af8a11448f79..eac8e61fb724a275282bd6c803398f75698ff78d 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -10,6 +10,7 @@
 #include <algorithm>
 #include <limits>
 #include <memory>
+#include <numeric>
 #include <set>
 #include <string>
 #include <vector>
@@ -403,6 +404,7 @@ GLRenderer::GLRenderer(const RendererSettings* settings,
   use_blend_equation_advanced_ = context_caps.blend_equation_advanced;
   use_blend_equation_advanced_coherent_ =
       context_caps.blend_equation_advanced_coherent;
+  use_occlusion_query_ = context_caps.occlusion_query;
 
   InitializeSharedObjects();
 }
@@ -3558,6 +3560,10 @@ void GLRenderer::FlushOverdrawFeedback(const DrawingFrame* frame,
   if (frame->current_render_pass != frame->root_render_pass)
     tracing_enabled = false;
 
+  // ARB_occlusion_query is required for tracing.
+  if (!use_occlusion_query_)
+    tracing_enabled = false;
+
   OverdrawFeedbackCallback overdraw_feedback_callback = base::Bind(
       &GLRenderer::ProcessOverdrawFeedback, weak_ptr_factory_.GetWeakPtr(),
       base::Owned(new std::vector<int>), arraysize(stencil_tests));
@@ -3566,8 +3572,7 @@ void GLRenderer::FlushOverdrawFeedback(const DrawingFrame* frame,
     GLuint query = 0;
     if (tracing_enabled) {
       gl_->GenQueriesEXT(1, &query);
-      // TODO(reveman): Use SAMPLES_PASSED_ARB for exact amount of overdraw.
-      gl_->BeginQueryEXT(GL_ANY_SAMPLES_PASSED_EXT, query);
+      gl_->BeginQueryEXT(GL_SAMPLES_PASSED_ARB, query);
     }
 
     gl_->StencilFunc(test.func, test.ref, 0xffffffff);
@@ -3578,7 +3583,7 @@ void GLRenderer::FlushOverdrawFeedback(const DrawingFrame* frame,
     gl_->DrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, 0);
 
     if (query) {
-      gl_->EndQueryEXT(GL_ANY_SAMPLES_PASSED_EXT);
+      gl_->EndQueryEXT(GL_SAMPLES_PASSED_ARB);
       context_support_->SignalQuery(
           query,
           base::Bind(overdraw_feedback_callback, query, test.multiplier));
@@ -3593,7 +3598,6 @@ void GLRenderer::ProcessOverdrawFeedback(std::vector<int>* overdraw,
   unsigned result = 0;
   if (query) {
     gl_->GetQueryObjectuivEXT(query, GL_QUERY_RESULT_EXT, &result);
-    DCHECK_LE(result, 1u);
     gl_->DeleteQueriesEXT(1, &query);
   }
 
@@ -3604,9 +3608,12 @@ void GLRenderer::ProcessOverdrawFeedback(std::vector<int>* overdraw,
   if (overdraw->size() < num_expected_results)
     return;
 
-  // Report the maximum amount of overdraw.
-  TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("cc.debug.overdraw"), "GPU Overdraw",
-                 *std::max_element(overdraw->begin(), overdraw->end()));
+  // Report GPU overdraw as a percentage of the surface size. ie. 2x overdraw
+  // for the whole screen is reported as 200.
+  TRACE_COUNTER1(
+      TRACE_DISABLED_BY_DEFAULT("cc.debug.overdraw"), "GPU Overdraw",
+      (std::accumulate(overdraw->begin(), overdraw->end(), 0) * 100) /
+          current_surface_size_.GetArea());

[danakj, 2017/01/18 19:34:06]

I don't think you can/should use a member variable like this here. You should
pass the size in when the query is bound or you have a race if it changes.

[reveman, 2017/01/18 20:05:28]

Done.

 }
 
 }  // namespace cc