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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 DOM_SMIL_SMILCOMPOSITOR_H_
+#define DOM_SMIL_SMILCOMPOSITOR_H_
+
+#include <utility>
+
+#include "PLDHashTable.h"
+#include "SMILTargetIdentifier.h"
+#include "mozilla/SMILAnimationFunction.h"
+#include "mozilla/SMILCompositorTable.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCSSPropertyID.h"
+#include "nsString.h"
+#include "nsTHashtable.h"
+
+namespace mozilla {
+
+class ComputedStyle;
+
+//----------------------------------------------------------------------
+// SMILCompositor
+//
+// Performs the composition of the animation sandwich by combining the results
+// of a series animation functions according to the rules of SMIL composition
+// including prioritising animations.
+
+class SMILCompositor : public PLDHashEntryHdr {
+ public:
+  using KeyType = SMILTargetIdentifier;
+  using KeyTypeRef = const KeyType&;
+  using KeyTypePointer = const KeyType*;
+
+  explicit SMILCompositor(KeyTypePointer aKey)
+      : mKey(*aKey), mForceCompositing(false) {}
+  SMILCompositor(SMILCompositor&& toMove) noexcept
+      : PLDHashEntryHdr(std::move(toMove)),
+        mKey(std::move(toMove.mKey)),
+        mAnimationFunctions(std::move(toMove.mAnimationFunctions)),
+        mForceCompositing(false) {}
+
+  // PLDHashEntryHdr methods
+  KeyTypeRef GetKey() const { return mKey; }
+  bool KeyEquals(KeyTypePointer aKey) const;
+  static KeyTypePointer KeyToPointer(KeyTypeRef aKey) { return &aKey; }
+  static PLDHashNumber HashKey(KeyTypePointer aKey);
+  enum { ALLOW_MEMMOVE = false };
+
+  // Adds the given animation function to this Compositor's list of functions
+  void AddAnimationFunction(SMILAnimationFunction* aFunc);
+
+  // Composes the attribute's current value with the list of animation
+  // functions, and assigns the resulting value to this compositor's target
+  // attribute. If a change is made that might produce style updates,
+  // aMightHavePendingStyleUpdates is set to true. Otherwise it is not modified.
+  void ComposeAttribute(bool& aMightHavePendingStyleUpdates);
+
+  // Clears animation effects on my target attribute
+  void ClearAnimationEffects();
+
+  // Cycle-collection support
+  void Traverse(nsCycleCollectionTraversalCallback* aCallback);
+
+  // Toggles a bit that will force us to composite (bypassing early-return
+  // optimizations) when we hit ComposeAttribute.
+  void ToggleForceCompositing() { mForceCompositing = true; }
+
+  // Transfers |aOther|'s mCachedBaseValue to |this|
+  void StealCachedBaseValue(SMILCompositor* aOther) {
+    mCachedBaseValue = std::move(aOther->mCachedBaseValue);
+  }
+
+ private:
+  // Create a SMILAttr for my target, on the heap.
+  //
+  // @param aBaseComputedStyle  An optional ComputedStyle which, if set, will be
+  //                           used when fetching the base style.
+  UniquePtr<SMILAttr> CreateSMILAttr(ComputedStyle* aBaseComputedStyle);
+
+  // Returns the CSS property this compositor should animate, or
+  // eCSSProperty_UNKNOWN if this compositor does not animate a CSS property.
+  nsCSSPropertyID GetCSSPropertyToAnimate() const;
+
+  // Returns true if we might need to refer to base styles (i.e. we are
+  // targeting a CSS property and have one or more animation functions that
+  // don't just replace the underlying value).
+  //
+  // This might return true in some cases where we don't actually need the base
+  // style since it doesn't build up the animation sandwich to check if the
+  // functions that appear to need the base style are actually replaced by
+  // a function further up the stack.
+  bool MightNeedBaseStyle() const;
+
+  // Finds the index of the first function that will affect our animation
+  // sandwich. Also toggles the 'mForceCompositing' flag if it finds that any
+  // (used) functions have changed.
+  uint32_t GetFirstFuncToAffectSandwich();
+
+  // If the passed-in base value differs from our cached base value, this
+  // method updates the cached value (and toggles the 'mForceCompositing' flag)
+  void UpdateCachedBaseValue(const SMILValue& aBaseValue);
+
+  // The hash key (tuple of element and attributeName)
+  KeyType mKey;
+
+  // Hash Value: List of animation functions that animate the specified attr
+  nsTArray<SMILAnimationFunction*> mAnimationFunctions;
+
+  // Member data for detecting when we need to force-recompose
+  // ---------------------------------------------------------
+  // Flag for tracking whether we need to compose. Initialized to false, but
+  // gets flipped to true if we detect that something has changed.
+  bool mForceCompositing;
+
+  // Cached base value, so we can detect & force-recompose when it changes
+  // from one sample to the next. (SMILAnimationController moves this
+  // forward from the previous sample's compositor by calling
+  // StealCachedBaseValue.)
+  SMILValue mCachedBaseValue;
+};
+
+}  // namespace mozilla
+
+#endif  // DOM_SMIL_SMILCOMPOSITOR_H_