Use the regular layer tree for fullscreen low power detachment on Mac.

Fixes an issue where fullscreen video wasn't positioned correctly in the
low power tree for some sites, and a longstanding issue where clipped
videos become un-clipped in the fullscreen low power tree.

Made possible by two changes:

- Black and transparent backgrounds are no longer rendered as IOSurfaces
  for color correction. For macOS to consider a layer solid black, it
  needs to actually have a black background color (and no contents).
  Note: I think we can avoid IOSurface replacement by setting a flag or
  two on the CAContext. See https://crrev.com/c/742663.

- Instead of constructing a new layer tree for fullscreen low power,
  just make the root layer black and match its size to the background to
  meet the "opaque black superlayer" requirement for detachment. A nicer
  solution could be to send the browser a color, since it already has a
  solid color superlayer, in which case no special handling for
  fullscreen layer detachment would be needed at all, it would "just
  work". It still needs to be determined whether that would comply with
  the HTML fullscreen spec. See https://crbug.com/785001.

Bug: 781637
Change-Id: I94abb1ade9c58c218296a27f9a7bc3630d4a0c64
Reviewed-on: https://chromium-review.googlesource.com/775139
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Reviewed-by: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517879}

ui/accelerated_widget_mac/ca_renderer_layer_tree.h

@@ -94,20 +94,17 @@ class ACCELERATED_WIDGET_MAC_EXPORT CARendererLayerTree {
                     RootLayer* old_layer,
                     float scale_factor);
 
-    // Check to see if the CALayer tree can be represented entirely by a video
-    // layer on a black background. If so, then commit the layer, assign it to
-    // |low_power_layer|, and return true. Otherwise return false. This is to
-    // be called by CommitToCA().
-    bool CommitFullscreenLowPowerLayer(ContentLayer* old_low_power_layer,
-                                       float scale_factor);
+    // Check to see if the CALayer tree is just a video layer on a black
+    // background. If so, return true and set background_rect to the
+    // background's bounding rect, otherwise return false. CommitToCA() calls
+    // this function and, based on its return value, either gives the root
+    // layer this frame and a black background color or clears them.
+    bool WantsFullcreenLowPowerBackdrop(float scale_factor,
+                                        gfx::RectF* background_rect);
 
     std::vector<ClipAndSortingLayer> clip_and_sorting_layers;
     base::scoped_nsobject<CALayer> ca_layer;
 
-    // Weak pointer to a child ContentLayer, if any, which is presented alone
-    // for fullscreen low power mode. Set by CommitFullscreenLowPowerLayer().
-    ContentLayer* low_power_layer = nullptr;
-
    private:
     DISALLOW_COPY_AND_ASSIGN(RootLayer);
   };

ui/accelerated_widget_mac/ca_renderer_layer_tree.mm

@@ -218,31 +218,24 @@ void CARendererLayerTree::CommitScheduledCALayers(
   scale_factor_ = scale_factor;
 }
 
-bool CARendererLayerTree::RootLayer::CommitFullscreenLowPowerLayer(
-    ContentLayer* old_low_power_layer,
-    float scale_factor) {
-  ContentLayer* video_layer = nullptr;
-  CGRect clip_rect;
-  CGRect frame_rect;
+bool CARendererLayerTree::RootLayer::WantsFullcreenLowPowerBackdrop(
+    float scale_factor,
+    gfx::RectF* background_rect) {
+  bool found_video_layer = false;
   for (auto& clip_layer : clip_and_sorting_layers) {
     for (auto& transform_layer : clip_layer.transform_layers) {
       for (auto& content_layer : transform_layer.content_layers) {
         // Detached mode requires that no layers be on top of the video layer.
-        if (video_layer)
+        if (found_video_layer)
           return false;
 
         // See if this is the video layer.
         if (content_layer.use_av_layer) {
-          video_layer = &content_layer;
+          found_video_layer = true;
           if (!transform_layer.transform.IsPositiveScaleOrTranslation())
             return false;
           if (content_layer.opacity != 1)
             return false;
-          clip_rect = clip_layer.clip_rect.ToCGRect();
-          gfx::RectF frame_rect_f(video_layer->rect);
-          transform_layer.transform.TransformRect(&frame_rect_f);
-          frame_rect_f.Scale(1 / scale_factor);
-          frame_rect = frame_rect_f.ToCGRect();
           continue;
         }
 
@@ -250,25 +243,16 @@ bool CARendererLayerTree::RootLayer::CommitFullscreenLowPowerLayer(
         // solid black or transparent
         if (content_layer.io_surface)
           return false;
-        if (content_layer.background_color != SK_ColorBLACK &&
-            content_layer.background_color != SK_ColorTRANSPARENT) {
+        if (content_layer.background_color == SK_ColorBLACK) {
+          background_rect->Union(gfx::RectF(content_layer.rect));
+        } else if (content_layer.background_color != SK_ColorTRANSPARENT) {
           return false;
         }
       }
     }
   }
-  if (!video_layer)
-    return false;
-  low_power_layer = video_layer;
-
-  low_power_layer->CommitToCA(ca_layer, old_low_power_layer, scale_factor);
-  if (![ca_layer backgroundColor])
-    [ca_layer setBackgroundColor:CGColorGetConstantColor(kCGColorBlack)];
-  if (!CGRectEqualToRect([ca_layer frame], clip_rect))
-    [ca_layer setFrame:clip_rect];
-  if (!CGRectEqualToRect([low_power_layer->ca_layer frame], frame_rect))
-    [low_power_layer->ca_layer setFrame:frame_rect];
-  return true;
+  background_rect->Scale(1 / scale_factor);
+  return found_video_layer;
 }
 
 id CARendererLayerTree::ContentsForSolidColorForTesting(SkColor color) {
@@ -377,9 +361,13 @@ CARendererLayerTree::ContentLayer::ContentLayer(
   // output monitor color space, but IOSurface-backed layers are color
   // corrected. Note that this is only the case when the CALayers are shared
   // across processes. To make colors consistent across both solid color and
-  // IOSurface-backed layers, use a cache of solid-color IOSurfaces as contents.
+  // IOSurface-backed layers, use a cache of solid-color IOSurfaces as
+  // contents. Black and transparent layers must use real colors to be eligible
+  // for low power detachment in fullscreen.
   // https://crbug.com/633805
-  if (!io_surface && !tree->allow_solid_color_layers_) {
+  if (!io_surface && !tree->allow_solid_color_layers_ &&
+      background_color != SK_ColorBLACK &&
+      background_color != SK_ColorTRANSPARENT) {
     solid_color_contents = SolidColorContents::Get(background_color);
     ContentLayer::contents_rect = gfx::RectF(0, 0, 1, 1);
   }
@@ -529,18 +517,17 @@ void CARendererLayerTree::RootLayer::CommitToCA(CALayer* superlayer,
     DLOG(ERROR) << "CARendererLayerTree root layer not attached to tree.";
   }
 
-  ContentLayer* old_low_power_layer =
-      old_layer ? old_layer->low_power_layer : nullptr;
-
-  if (CommitFullscreenLowPowerLayer(old_low_power_layer, scale_factor)) {
-    return;
-  } else if (old_low_power_layer) {
-    // Transitioning out of fullscreen low power mode, so:
-    // 1. Reset the root CALayer's background color and frame.
-    [ca_layer setBackgroundColor:nil];
-    [ca_layer setFrame:CGRectZero];
-    // 2. Reset old_layer so that the CALayer tree is rebuilt from scratch.
-    old_layer = nullptr;
+  gfx::RectF bg_rect;
+  if (WantsFullcreenLowPowerBackdrop(scale_factor, &bg_rect)) {
+    if (gfx::RectF([ca_layer frame]) != bg_rect)
+      [ca_layer setFrame:bg_rect.ToCGRect()];
+    if (![ca_layer backgroundColor])
+      [ca_layer setBackgroundColor:CGColorGetConstantColor(kCGColorBlack)];
+  } else {
+    if (gfx::RectF([ca_layer frame]) != gfx::RectF())
+      [ca_layer setFrame:CGRectZero];
+    if ([ca_layer backgroundColor])
+      [ca_layer setBackgroundColor:nil];
   }
 
   for (size_t i = 0; i < clip_and_sorting_layers.size(); ++i) {