cc: Implement overdraw feedback debugging feature.

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 e1020caf4def2e10973e8c65449ed1ea1a6b3b37..140153a574e7a01a7074304422824cd97f5dab73 100644
--- a/cc/output/gl_renderer.cc
+++ b/cc/output/gl_renderer.cc
@@ -14,6 +14,7 @@
 #include <string>
 #include <vector>
 
+#include "base/barrier_closure.h"
 #include "base/feature_list.h"
 #include "base/logging.h"
 #include "base/macros.h"
@@ -370,6 +371,16 @@ class GLRenderer::SyncQuery {
   DISALLOW_COPY_AND_ASSIGN(SyncQuery);
 };
 
+struct GLRenderer::PendingOverdrawQuery {
+  explicit PendingOverdrawQuery(unsigned query) : query(query) {}
+
+  base::CancelableClosure overdraw_callback;
+  const unsigned query;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PendingOverdrawQuery);
+};
+
 GLRenderer::GLRenderer(const RendererSettings* settings,
                        OutputSurface* output_surface,
                        ResourceProvider* resource_provider,
@@ -415,6 +426,13 @@ GLRenderer::~GLRenderer() {
     pending_async_read_pixels_.pop_back();
   }
 
+  while (!pending_overdraw_queries_.empty()) {
+    PendingOverdrawQuery* pending_query =
+        pending_overdraw_queries_.back().get();
+    pending_query->overdraw_callback.Cancel();
+    pending_overdraw_queries_.pop_back();
+  }
+
   CleanupSharedObjects();
 
   if (context_visibility_) {
@@ -425,6 +443,13 @@ GLRenderer::~GLRenderer() {
 }
 
 bool GLRenderer::CanPartialSwap() {
+  bool overdraw_tracing_enabled;
+  TRACE_EVENT_CATEGORY_GROUP_ENABLED(
+      TRACE_DISABLED_BY_DEFAULT("cc.debug.overdraw"),
+      &overdraw_tracing_enabled);
+  // Overdraw tracing requires fullscreen updates.
+  if (overdraw_tracing_enabled)
+    return false;
   auto* context_provider = output_surface_->context_provider();
   return context_provider->ContextCapabilities().post_sub_buffer;
 }
@@ -495,7 +520,9 @@ void GLRenderer::ClearFramebuffer(DrawingFrame* frame) {
   else
     gl_->ClearColor(0, 0, 1, 1);
 
-  bool always_clear = false;
+  gl_->ClearStencil(0);
+
+  bool always_clear = overdraw_feedback_;
 #ifndef NDEBUG
   always_clear = true;
 #endif
@@ -2763,8 +2790,11 @@ void GLRenderer::FinishDrawingFrame(DrawingFrame* frame) {
     pending_sync_queries_.push_back(std::move(current_sync_query_));
   }
 
-  current_framebuffer_lock_ = nullptr;
   swap_buffer_rect_.Union(frame->root_damage_rect);
+  if (overdraw_feedback_)
+    FlushOverdrawFeedback(frame, swap_buffer_rect_);
+
+  current_framebuffer_lock_ = nullptr;
 
   gl_->Disable(GL_BLEND);
   blend_shadow_ = false;
@@ -3002,6 +3032,9 @@ void GLRenderer::GetFramebufferPixelsAsync(
   if (rect.IsEmpty())
     return;
 
+  if (overdraw_feedback_)
+    FlushOverdrawFeedback(frame, rect);
+
   gfx::Rect window_rect = MoveFromDrawToWindowSpace(frame, rect);
   DCHECK_GE(window_rect.x(), 0);
   DCHECK_GE(window_rect.y(), 0);
@@ -3202,7 +3235,10 @@ void GLRenderer::BindFramebufferToOutputSurface(DrawingFrame* frame) {
   current_framebuffer_lock_ = nullptr;
   output_surface_->BindFramebuffer();
 
-  if (output_surface_->HasExternalStencilTest()) {
+  if (overdraw_feedback_) {
+    SetupOverdrawFeedback();
+    SetStencilEnabled(true);
+  } else if (output_surface_->HasExternalStencilTest()) {
     output_surface_->ApplyExternalStencil();
     SetStencilEnabled(true);
   } else {
@@ -3218,7 +3254,6 @@ bool GLRenderer::BindFramebufferToTexture(DrawingFrame* frame,
   // same texture again.
   current_framebuffer_lock_ = nullptr;
 
-  SetStencilEnabled(false);
   gl_->BindFramebuffer(GL_FRAMEBUFFER, offscreen_framebuffer_id_);
   current_framebuffer_lock_ =
       base::MakeUnique<ResourceProvider::ScopedWriteLockGL>(
@@ -3227,10 +3262,31 @@ bool GLRenderer::BindFramebufferToTexture(DrawingFrame* frame,
   unsigned texture_id = current_framebuffer_lock_->texture_id();
   gl_->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
                             texture_id, 0);
+  if (overdraw_feedback_) {
+    if (texture->size() != offscreen_stencil_renderbuffer_size_) {
+      gl_->BindRenderbuffer(GL_RENDERBUFFER,
+                            offscreen_stencil_renderbuffer_id_);
+      gl_->RenderbufferStorage(GL_RENDERBUFFER, GL_STENCIL_INDEX8,
+                               texture->size().width(),
+                               texture->size().height());
+      gl_->BindRenderbuffer(GL_RENDERBUFFER, 0);
+      offscreen_stencil_renderbuffer_size_ = texture->size();
+    }
+    gl_->FramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT,
+                                 GL_RENDERBUFFER,
+                                 offscreen_stencil_renderbuffer_id_);
+  }
 
   DCHECK(gl_->CheckFramebufferStatus(GL_FRAMEBUFFER) ==
              GL_FRAMEBUFFER_COMPLETE ||
          IsContextLost());
+
+  if (overdraw_feedback_) {
+    SetupOverdrawFeedback();
+    SetStencilEnabled(true);
+  } else {
+    SetStencilEnabled(false);
+  }
   return true;
 }
 
@@ -3261,6 +3317,9 @@ void GLRenderer::InitializeSharedObjects() {
   // Create an FBO for doing offscreen rendering.
   gl_->GenFramebuffers(1, &offscreen_framebuffer_id_);
 
+  // Create a stencil buffer for doing offscreen rendering.
+  gl_->GenRenderbuffers(1, &offscreen_stencil_renderbuffer_id_);

[Daniele Castagna, 2017/01/09 18:53:06]

Why not if (overdraw_feedback_) ?

[reveman, 2017/01/10 23:52:00]

Done. By deferring this until needed.

+
   shared_geometry_ =
       base::MakeUnique<StaticGeometryBinding>(gl_, QuadVertexRect());
   clipped_geometry_ = base::MakeUnique<DynamicGeometryBinding>(gl_);
@@ -3732,6 +3791,9 @@ void GLRenderer::CleanupSharedObjects() {
   if (offscreen_framebuffer_id_)
     gl_->DeleteFramebuffers(1, &offscreen_framebuffer_id_);
 
+  if (offscreen_stencil_renderbuffer_id_)
+    gl_->DeleteRenderbuffers(1, &offscreen_stencil_renderbuffer_id_);
+
   ReleaseRenderPassTextures();
 }
 
@@ -4064,4 +4126,137 @@ void GLRenderer::ScheduleRenderPassDrawQuad(
       ca_layer_overlay->edge_aa_mask, bounds_rect, filter);
 }
 
+void GLRenderer::SetupOverdrawFeedback() {
+  gl_->StencilFunc(GL_ALWAYS, 1, 0xffffffff);
+  // First two values are ignored as test always passes.
+  gl_->StencilOp(GL_KEEP, GL_KEEP, GL_INCR);
+  gl_->StencilMask(0xff);
+}
+
+void GLRenderer::FlushOverdrawFeedback(const DrawingFrame* frame,
+                                       const gfx::Rect& output_rect) {
+  // Return early if already flushed.
+  if (!stencil_shadow_)
+    return;
+
+  // Test only, keep everything.
+  gl_->StencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
+  gl_->StencilMask(0);
+
+  EnsureScissorTestDisabled();
+  SetBlendEnabled(true);
+
+  PrepareGeometry(SHARED_BINDING);
+
+  const DebugBorderProgram* program = GetDebugBorderProgram();
+  DCHECK(program && (program->initialized() || IsContextLost()));
+  SetUseProgram(program->program());
+
+  gfx::Transform render_matrix;
+  render_matrix.Translate(0.5 * output_rect.width() + output_rect.x(),
+                          0.5 * output_rect.height() + output_rect.y());
+  render_matrix.Scale(output_rect.width(), output_rect.height());
+  static float gl_matrix[16];
+  GLRenderer::ToGLMatrix(&gl_matrix[0],
+                         frame->projection_matrix * render_matrix);
+  gl_->UniformMatrix4fv(program->vertex_shader().matrix_location(), 1, false,
+                        &gl_matrix[0]);
+
+  // Produce hinting for the amount of overdraw on screen for each pixel by
+  // drawing hint colors to the framebuffer based on the current stencil value.
+  struct {
+    int category;
+    GLenum func;
+    GLint ref;
+    SkColor color;
+  } stencil_tests[] = {
+      {1, GL_EQUAL, 2, 0x2f0000ff},  // Blue: Overdrawn once.
+      {2, GL_EQUAL, 3, 0x2f00ff00},  // Green: Overdrawn twice.
+      {3, GL_EQUAL, 4, 0x3fff0000},  // Pink: Overdrawn three times.
+      {4, GL_LESS, 4, 0x7fff0000},   // Red: Overdrawn four or more times.
+  };
+
+  // Occlusion queries can be expensive, so only collect trace data if we select
+  // cc.debug.overdraw.
+  bool tracing_enabled;
+  TRACE_EVENT_CATEGORY_GROUP_ENABLED(
+      TRACE_DISABLED_BY_DEFAULT("cc.debug.overdraw"), &tracing_enabled);
+
+  // Trace only the root render pass.
+  if (frame->current_render_pass != frame->root_render_pass)
+    tracing_enabled = false;
+
+  base::Closure barrier = base::BarrierClosure(
+      arraysize(stencil_tests),
+      base::Bind(&GLRenderer::UpdateOverdrawCounter, base::Unretained(this)));
+
+  for (const auto& test : stencil_tests) {
+    if (tracing_enabled) {
+      GLuint query = 0;
+      gl_->GenQueriesEXT(1, &query);
+      // TODO(reveman): Use SAMPLES_PASSED_ARB when available for exact amount
+      // of overdraw.
+      gl_->BeginQueryEXT(GL_ANY_SAMPLES_PASSED_EXT, query);
+
+      std::unique_ptr<PendingOverdrawQuery> pending_overdraw_query(
+          new PendingOverdrawQuery(query));
+      pending_overdraw_queries_.push_back(std::move(pending_overdraw_query));
+    }
+
+    gl_->StencilFunc(test.func, test.ref, 0xffffffff);
+    Float4 color = PremultipliedColor(test.color);
+    gl_->Uniform4fv(program->fragment_shader().color_location(), 1, color.data);
+    gl_->DrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, 0);
+
+    if (tracing_enabled) {
+      base::Closure overdraw_feedback_callback = base::Bind(
+          &GLRenderer::OverdrawFeedback, base::Unretained(this),
+          pending_overdraw_queries_.back()->query, test.category, barrier);
+
+      // Save the overdraw_feedback_callback so it can be cancelled.
+      pending_overdraw_queries_.back()->overdraw_callback.Reset(
+          overdraw_feedback_callback);
+      base::Closure cancelable_callback =
+          pending_overdraw_queries_.back()->overdraw_callback.callback();
+
+      gl_->EndQueryEXT(GL_ANY_SAMPLES_PASSED_EXT);
+      context_support_->SignalQuery(pending_overdraw_queries_.back()->query,
+                                    cancelable_callback);
+    }
+  }
+
+  gl_->StencilFunc(GL_ALWAYS, 0, 0xffffffff);
+  gl_->Disable(GL_STENCIL_TEST);
+  stencil_shadow_ = false;
+}
+
+void GLRenderer::OverdrawFeedback(unsigned query,
+                                  int category,
+                                  base::Closure barrier) {
+  DCHECK(!pending_overdraw_queries_.empty());
+  DCHECK_EQ(pending_overdraw_queries_.front()->query, query);
+  pending_overdraw_queries_.pop_front();
+
+  unsigned result = 0;
+  if (query) {
+    gl_->GetQueryObjectuivEXT(query, GL_QUERY_RESULT_EXT, &result);
+    gl_->DeleteQueriesEXT(1, &query);
+  }
+
+  if (result)
+    current_overdraw_.insert(category);
+  else
+    current_overdraw_.erase(category);
+
+  barrier.Run();
+}
+
+void GLRenderer::UpdateOverdrawCounter() const {
+  // Report overdraw as multiple of the screen size. ie. 1x for the whole
+  // screen is 1.0. Note: this will always report the worst overdraw on screen
+  // as the overdraw for the whole screen until SAMPLES_PASSED_ARB is supported.
+  TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("cc.debug.overdraw"), "GPU Overdraw",
+                 current_overdraw_.empty() ? 0 : *current_overdraw_.rbegin());
+}
+
 }  // namespace cc