1 files changed, 141 insertions, 0 deletions
diff --git a/layout/base/ActiveLayerTracker.h b/layout/base/ActiveLayerTracker.h
new file mode 100644
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+++ b/layout/base/ActiveLayerTracker.h
@@ -0,0 +1,141 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef ACTIVELAYERTRACKER_H_
+#define ACTIVELAYERTRACKER_H_
+
+#include "nsCSSPropertyID.h"
+
+class nsIFrame;
+class nsIContent;
+class nsDisplayListBuilder;
+class nsDOMCSSDeclaration;
+
+namespace mozilla {
+
+/**
+ * This class receives various notifications about style changes and content
+ * changes that affect layerization decisions, and implements the heuristics
+ * that drive those decisions. It manages per-frame state to support those
+ * heuristics.
+ */
+class ActiveLayerTracker {
+public:
+  static void Shutdown();
+
+  /*
+   * We track style changes to selected styles:
+   *   eCSSProperty_transform
+   *   eCSSProperty_opacity
+   *   eCSSProperty_left, eCSSProperty_top, eCSSProperty_right, eCSSProperty_bottom
+   * and use that information to guess whether style changes are animated.
+   */
+
+  /**
+   * Notify aFrame's style property as having changed due to a restyle,
+   * and therefore possibly wanting an active layer to render that style.
+   * Any such marking will time out after a short period.
+   * @param aProperty the property that has changed
+   */
+  static void NotifyRestyle(nsIFrame* aFrame, nsCSSPropertyID aProperty);
+  /**
+   * Notify aFrame's left/top/right/bottom properties as having (maybe)
+   * changed due to a restyle, and therefore possibly wanting an active layer
+   * to render that style. Any such marking will time out after a short period.
+   */
+  static void NotifyOffsetRestyle(nsIFrame* aFrame);
+  /**
+   * Mark aFrame as being known to have an animation of aProperty.
+   * Any such marking will time out after a short period.
+   * aNewValue and aDOMCSSDecl are used to determine whether the property's
+   * value has changed.
+   */
+  static void NotifyAnimated(nsIFrame* aFrame, nsCSSPropertyID aProperty,
+                             const nsAString& aNewValue,
+                             nsDOMCSSDeclaration* aDOMCSSDecl);
+  /**
+   * Notify aFrame as being known to have an animation of aProperty through an
+   * inline style modification during aScrollFrame's scroll event handler.
+   */
+  static void NotifyAnimatedFromScrollHandler(nsIFrame* aFrame, nsCSSPropertyID aProperty,
+                                              nsIFrame* aScrollFrame);
+  /**
+   * Notify that a property in the inline style rule of aFrame's element
+   * has been modified.
+   * This notification is incomplete --- not all modifications to inline
+   * style will trigger this.
+   * aNewValue and aDOMCSSDecl are used to determine whether the property's
+   * value has changed.
+   */
+  static void NotifyInlineStyleRuleModified(nsIFrame* aFrame, nsCSSPropertyID aProperty,
+                                            const nsAString& aNewValue,
+                                            nsDOMCSSDeclaration* aDOMCSSDecl);
+  /**
+   * Return true if aFrame's aProperty style should be considered as being animated
+   * for pre-rendering.
+   */
+  static bool IsStyleMaybeAnimated(nsIFrame* aFrame, nsCSSPropertyID aProperty);
+  /**
+   * Return true if aFrame's aProperty style should be considered as being animated
+   * for constructing active layers.
+   */
+  static bool IsStyleAnimated(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                              nsCSSPropertyID aProperty);
+  /**
+   * Return true if any of aFrame's offset property styles should be considered
+   * as being animated for constructing active layers.
+   */
+  static bool IsOffsetOrMarginStyleAnimated(nsIFrame* aFrame);
+  /**
+   * Return true if aFrame's background-position-x or background-position-y
+   * property is animated.
+   */
+  static bool IsBackgroundPositionAnimated(nsDisplayListBuilder* aBuilder,
+                                           nsIFrame* aFrame);
+  /**
+   * Return true if aFrame either has an animated scale now, or is likely to
+   * have one in the future because it has a CSS animation or transition
+   * (which may not be playing right now) that affects its scale.
+   */
+  static bool IsScaleSubjectToAnimation(nsIFrame* aFrame);
+
+  /**
+   * Transfer the LayerActivity property to the frame's content node when the
+   * frame is about to be destroyed so that layer activity can be tracked
+   * throughout reframes of an element. Only call this when aFrame is the
+   * primary frame of aContent.
+   */
+  static void TransferActivityToContent(nsIFrame* aFrame, nsIContent* aContent);
+  /**
+   * Transfer the LayerActivity property back to the content node's primary
+   * frame after the frame has been created.
+   */
+  static void TransferActivityToFrame(nsIContent* aContent, nsIFrame* aFrame);
+
+  /*
+   * We track modifications to the content of certain frames (i.e. canvas frames)
+   * and use that to make layering decisions.
+   */
+
+  /**
+   * Mark aFrame's content as being active. This marking will time out after
+   * a short period.
+   */
+  static void NotifyContentChange(nsIFrame* aFrame);
+  /**
+   * Return true if this frame's content is still marked as active.
+   */
+  static bool IsContentActive(nsIFrame* aFrame);
+
+  /**
+   * Called before and after a scroll event handler is executed, with the
+   * scrollframe or nullptr, respectively. This acts as a hint to treat
+   * inline style changes during the handler differently.
+   */
+  static void SetCurrentScrollHandlerFrame(nsIFrame* aFrame);
+};
+
+} // namespace mozilla
+
+#endif /* ACTIVELAYERTRACKER_H_ */