Fix HUD location and size when displaying the FPS meter

The author of https://crrev.com/588577 did not realize the HUD layer
could be used for non-full-viewport rect debug information such as the
FPS meter. This patch restores the non-rect size logic from
https://crrev.com/588577 and adds a test of the FPS meter size.

Bug: 894717
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ied6d6c80e396ab59dbc201994db5214ed1db09a0
Reviewed-on: https://chromium-review.googlesource.com/c/1277658Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599282}

cc/layers/heads_up_display_layer.cc

@@ -8,6 +8,7 @@
 
 #include "base/trace_event/trace_event.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
+#include "cc/trees/layer_tree_host.h"
 
 namespace cc {
 
@@ -27,6 +28,32 @@ HeadsUpDisplayLayer::HeadsUpDisplayLayer()
 
 HeadsUpDisplayLayer::~HeadsUpDisplayLayer() = default;
 
+void HeadsUpDisplayLayer::UpdateLocationAndSize(
+    const gfx::Size& device_viewport,
+    float device_scale_factor) {
+  gfx::Size device_viewport_in_layout_pixels =
+      gfx::Size(device_viewport.width() / device_scale_factor,
+                device_viewport.height() / device_scale_factor);
+
+  gfx::Size bounds;
+  gfx::Transform matrix;
+  matrix.MakeIdentity();
+
+  if (layer_tree_host()->GetDebugState().ShowHudRects()) {
+    bounds = device_viewport_in_layout_pixels;
+  } else {
+    // If the HUD is not displaying full-viewport rects (e.g., it is showing the
+    // FPS meter), use a fixed size.
+    constexpr int kDefaultHUDSize = 256;
+    bounds.SetSize(kDefaultHUDSize, kDefaultHUDSize);
+    matrix.Translate(device_viewport_in_layout_pixels.width() - kDefaultHUDSize,
+                     0.0);
+  }
+
+  SetBounds(bounds);
+  SetTransform(matrix);
+}
+
 bool HeadsUpDisplayLayer::HasDrawableContent() const {
   return true;
 }

cc/layers/heads_up_display_layer.h

@@ -20,6 +20,9 @@ class CC_EXPORT HeadsUpDisplayLayer : public Layer {
  public:
   static scoped_refptr<HeadsUpDisplayLayer> Create();
 
+  void UpdateLocationAndSize(const gfx::Size& device_viewport,
+                             float device_scale_factor);
+
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
 
   // Layer overrides.

cc/layers/heads_up_display_unittest.cc

@@ -82,5 +82,24 @@ class HudWithRootLayerChange : public HeadsUpDisplayTest {
 
 SINGLE_AND_MULTI_THREAD_TEST_F(HudWithRootLayerChange);
 
+class HeadsUpDisplaySizeWithFPS : public LayerTreeTest {
+ public:
+  void InitializeSettings(LayerTreeSettings* settings) override {
+    settings->initial_debug_state.show_fps_counter = true;
+  }
+
+  void BeginTest() override { PostSetNeedsCommitToMainThread(); }
+
+  void DidCommit() override {
+    ASSERT_TRUE(layer_tree_host()->hud_layer());
+    EXPECT_EQ(gfx::Size(256, 256), layer_tree_host()->hud_layer()->bounds());
+    EndTest();
+  }
+
+  void AfterTest() override {}
+};
+
+SINGLE_AND_MULTI_THREAD_TEST_F(HeadsUpDisplaySizeWithFPS);
+
 }  // namespace
 }  // namespace cc

cc/trees/layer_tree_host.cc

@@ -1412,14 +1412,10 @@ void LayerTreeHost::UpdateHudLayer(bool show_hud_info) {
   if (show_hud_info) {
     if (!hud_layer_.get())
       hud_layer_ = HeadsUpDisplayLayer::Create();
-
-    gfx::Size device_viewport_in_layout_pixels =
-        gfx::Size(device_viewport_size_.width() / device_scale_factor_,
-                  device_viewport_size_.height() / device_scale_factor_);
-    hud_layer_->SetBounds(device_viewport_in_layout_pixels);
-
     if (root_layer_.get() && !hud_layer_->parent())
       root_layer_->AddChild(hud_layer_);
+    hud_layer_->UpdateLocationAndSize(device_viewport_size_,
+                                      device_scale_factor_);
   } else if (hud_layer_.get()) {
     hud_layer_->RemoveFromParent();
     hud_layer_ = nullptr;

cc/trees/layer_tree_host.h

@@ -470,8 +470,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   void SetElasticOverscrollFromImplSide(gfx::Vector2dF elastic_overscroll);
   gfx::Vector2dF elastic_overscroll() const { return elastic_overscroll_; }
 
-  // Ensures a HUD layer exists if it is needed, and updates the layer bounds.
-  // If a HUD layer exists but is no longer needed, it is destroyed.
+  // Ensures a HUD layer exists if it is needed, and updates the HUD bounds and
+  // position. If a HUD layer exists but is no longer needed, it is destroyed.
   void UpdateHudLayer(bool show_hud_info);
   HeadsUpDisplayLayer* hud_layer() const { return hud_layer_.get(); }