1 files changed, 91 insertions, 0 deletions
diff --git a/layout/style/LayerAnimationInfo.h b/layout/style/LayerAnimationInfo.h
new file mode 100644
index 0000000000..8125d1442a
--- /dev/null
+++ b/layout/style/LayerAnimationInfo.h
@@ -0,0 +1,91 @@
+/* -*- 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 mozilla_LayerAnimationInfo_h
+#define mozilla_LayerAnimationInfo_h
+
+#include "nsChangeHint.h"
+#include "nsCSSPropertyID.h"
+#include "nsCSSPropertyIDSet.h"
+#include "nsDisplayItemTypes.h"  // For nsDisplayItem::Type
+#include "mozilla/Array.h"
+
+namespace mozilla {
+
+struct LayerAnimationInfo {
+  // Returns the corresponding display item type for |aProperty| when it is
+  // animated on the compositor.
+  // Returns DisplayItemType::TYPE_ZERO if |aProperty| cannot be animated on the
+  // compositor.
+  static DisplayItemType GetDisplayItemTypeForProperty(
+      nsCSSPropertyID aProperty);
+
+  // Returns the corresponding CSS properties for |aDisplayItemType|.
+  //
+  // This function works only for display items tied to CSS properties that can
+  // be animated on the compositor.
+  static inline const nsCSSPropertyIDSet& GetCSSPropertiesFor(
+      DisplayItemType aDisplayItemType) {
+    static const nsCSSPropertyIDSet transformProperties =
+        nsCSSPropertyIDSet::TransformLikeProperties();
+    static const nsCSSPropertyIDSet opacityProperties =
+        nsCSSPropertyIDSet{eCSSProperty_opacity};
+    static const nsCSSPropertyIDSet backgroundColorProperties =
+        nsCSSPropertyIDSet{eCSSProperty_background_color};
+    static const nsCSSPropertyIDSet empty = nsCSSPropertyIDSet();
+
+    switch (aDisplayItemType) {
+      case DisplayItemType::TYPE_BACKGROUND_COLOR:
+        return backgroundColorProperties;
+      case DisplayItemType::TYPE_OPACITY:
+        return opacityProperties;
+      case DisplayItemType::TYPE_TRANSFORM:
+        return transformProperties;
+      default:
+        MOZ_ASSERT_UNREACHABLE(
+            "Should not be called for display item types "
+            "that are not able to have animations on the "
+            "compositor");
+        return empty;
+    }
+  }
+
+  // Returns the appropriate change hint for updating the display item for
+  // |aDisplayItemType|.
+  //
+  // This function works only for display items tied to CSS properties that can
+  // be animated on the compositor.
+  static inline nsChangeHint GetChangeHintFor(
+      DisplayItemType aDisplayItemType) {
+    switch (aDisplayItemType) {
+      case DisplayItemType::TYPE_BACKGROUND_COLOR:
+        return nsChangeHint_RepaintFrame;
+      case DisplayItemType::TYPE_OPACITY:
+        return nsChangeHint_UpdateOpacityLayer;
+      case DisplayItemType::TYPE_TRANSFORM:
+        return nsChangeHint_UpdateTransformLayer;
+      default:
+        MOZ_ASSERT_UNREACHABLE(
+            "Should not be called for display item types "
+            "that are not able to have animations on the "
+            "compositor");
+        return nsChangeHint(0);
+    }
+  }
+
+  // An array of DisplayItemType corresponding to the display item that we can
+  // animate on the compositor.
+  //
+  // This is used to look up the appropriate change hint in cases when
+  // animations need updating but no other change hint is generated.
+  static const Array<DisplayItemType,
+                     nsCSSPropertyIDSet::CompositorAnimatableDisplayItemCount()>
+      sDisplayItemTypes;
+};
+
+}  // namespace mozilla
+
+#endif /* !defined(mozilla_LayerAnimationInfo_h) */