1 files changed, 44 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/ExpectedGeckoMetrics.h b/gfx/layers/apz/src/ExpectedGeckoMetrics.h
new file mode 100644
index 0000000000..ca5aa76eba
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+++ b/gfx/layers/apz/src/ExpectedGeckoMetrics.h
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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 mozilla_layers_ExpectedGeckoMetrics_h
+#define mozilla_layers_ExpectedGeckoMetrics_h
+
+#include "Units.h"
+
+namespace mozilla {
+namespace layers {
+
+struct FrameMetrics;
+
+// A class that stores a subset of the FrameMetrics information
+// than an APZC instance expects Gecko to have (either the
+// metrics that were most recently sent to Gecko, or the ones
+// most recently received from Gecko).
+class ExpectedGeckoMetrics {
+ public:
+  ExpectedGeckoMetrics() = default;
+  void UpdateFrom(const FrameMetrics& aMetrics);
+  void UpdateZoomFrom(const FrameMetrics& aMetrics);
+
+  const CSSPoint& GetVisualScrollOffset() const { return mVisualScrollOffset; }
+  const CSSPoint& GetLayoutScrollOffset() const { return mLayoutScrollOffset; }
+  const CSSToParentLayerScale& GetZoom() const { return mZoom; }
+  const CSSToLayoutDeviceScale& GetDevPixelsPerCSSPixel() const {
+    return mDevPixelsPerCSSPixel;
+  }
+
+ private:
+  CSSPoint mVisualScrollOffset;
+  CSSPoint mLayoutScrollOffset;
+  CSSToParentLayerScale mZoom;
+  CSSToLayoutDeviceScale mDevPixelsPerCSSPixel;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif