1 files changed, 154 insertions, 0 deletions
diff --git a/layout/generic/ScrollSnapInfo.h b/layout/generic/ScrollSnapInfo.h
new file mode 100644
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+++ b/layout/generic/ScrollSnapInfo.h
@@ -0,0 +1,154 @@
+/* -*- 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_layout_ScrollSnapInfo_h_
+#define mozilla_layout_ScrollSnapInfo_h_
+
+#include <memory>
+#include "mozilla/ScrollTypes.h"
+#include "mozilla/ScrollSnapTargetId.h"
+#include "mozilla/ServoStyleConsts.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/layers/LayersTypes.h"
+#include "nsPoint.h"
+
+class nsIContent;
+class nsIFrame;
+struct nsRect;
+struct nsSize;
+struct nsStyleDisplay;
+
+namespace mozilla {
+
+enum class StyleScrollSnapStrictness : uint8_t;
+class WritingMode;
+
+struct SnapPoint {
+  SnapPoint() = default;
+  explicit SnapPoint(const nsPoint& aPoint)
+      : mX(Some(aPoint.x)), mY(Some(aPoint.y)) {}
+  SnapPoint(Maybe<nscoord>&& aX, Maybe<nscoord>&& aY)
+      : mX(std::move(aX)), mY(std::move(aY)) {}
+
+  bool operator==(const SnapPoint& aOther) const {
+    return mX == aOther.mX && mY == aOther.mY;
+  }
+
+  Maybe<nscoord> mX;
+  Maybe<nscoord> mY;
+};
+
+struct ScrollSnapInfo {
+  using ScrollDirection = layers::ScrollDirection;
+  ScrollSnapInfo();
+
+  bool operator==(const ScrollSnapInfo& aOther) const {
+    return mScrollSnapStrictnessX == aOther.mScrollSnapStrictnessX &&
+           mScrollSnapStrictnessY == aOther.mScrollSnapStrictnessY &&
+           mSnapTargets == aOther.mSnapTargets &&
+           mXRangeWiderThanSnapport == aOther.mXRangeWiderThanSnapport &&
+           mYRangeWiderThanSnapport == aOther.mYRangeWiderThanSnapport &&
+           mSnapportSize == aOther.mSnapportSize;
+  }
+
+  bool HasScrollSnapping() const;
+  bool HasSnapPositions() const;
+
+  void InitializeScrollSnapStrictness(WritingMode aWritingMode,
+                                      const nsStyleDisplay* aDisplay);
+
+  // The scroll frame's scroll-snap-type.
+  StyleScrollSnapStrictness mScrollSnapStrictnessX;
+  StyleScrollSnapStrictness mScrollSnapStrictnessY;
+
+  struct SnapTarget {
+    // The scroll positions corresponding to scroll-snap-align values.
+    SnapPoint mSnapPoint;
+
+    // https://drafts.csswg.org/css-scroll-snap/#scroll-snap-area
+    nsRect mSnapArea;
+
+    // https://drafts.csswg.org/css-scroll-snap/#propdef-scroll-snap-stop
+    StyleScrollSnapStop mScrollSnapStop = StyleScrollSnapStop::Normal;
+
+    // Use for tracking the last snapped target.
+    ScrollSnapTargetId mTargetId = ScrollSnapTargetId::None;
+
+    SnapTarget() = default;
+
+    SnapTarget(Maybe<nscoord>&& aSnapPositionX, Maybe<nscoord>&& aSnapPositionY,
+               const nsRect& aSnapArea, StyleScrollSnapStop aScrollSnapStop,
+               ScrollSnapTargetId aTargetId)
+        : mSnapPoint(std::move(aSnapPositionX), std::move(aSnapPositionY)),
+          mSnapArea(aSnapArea),
+          mScrollSnapStop(aScrollSnapStop),
+          mTargetId(aTargetId) {}
+
+    bool operator==(const SnapTarget& aOther) const {
+      return mSnapPoint == aOther.mSnapPoint && mSnapArea == aOther.mSnapArea &&
+             mScrollSnapStop == aOther.mScrollSnapStop &&
+             mTargetId == aOther.mTargetId;
+    }
+  };
+
+  CopyableTArray<SnapTarget> mSnapTargets;
+
+  // A utility function to iterate over the valid snap targets for the given
+  // |aDestination| until |aFunc| returns false.
+  void ForEachValidTargetFor(
+      const nsPoint& aDestination,
+      const std::function<bool(const SnapTarget&)>& aFunc) const;
+
+  struct ScrollSnapRange {
+    ScrollSnapRange() = default;
+
+    ScrollSnapRange(const nsRect& aSnapArea, ScrollDirection aDirection,
+                    ScrollSnapTargetId aTargetId)
+        : mSnapArea(aSnapArea), mDirection(aDirection), mTargetId(aTargetId) {}
+
+    nsRect mSnapArea;
+    ScrollDirection mDirection;
+    ScrollSnapTargetId mTargetId;
+
+    bool operator==(const ScrollSnapRange& aOther) const {
+      return mDirection == aOther.mDirection && mSnapArea == aOther.mSnapArea &&
+             mTargetId == aOther.mTargetId;
+    }
+
+    nscoord Start() const {
+      return mDirection == ScrollDirection::eHorizontal ? mSnapArea.X()
+                                                        : mSnapArea.Y();
+    }
+
+    nscoord End() const {
+      return mDirection == ScrollDirection::eHorizontal ? mSnapArea.XMost()
+                                                        : mSnapArea.YMost();
+    }
+
+    // Returns true if |aPoint| is a valid snap position in this range.
+    bool IsValid(nscoord aPoint, nscoord aSnapportSize) const {
+      MOZ_ASSERT(End() - Start() > aSnapportSize);
+      return Start() <= aPoint && aPoint <= End() - aSnapportSize;
+    }
+  };
+  // An array of the range that the target element is larger than the snapport
+  // on the axis.
+  // Snap positions in this range will be valid snap positions in the case where
+  // the distance between the closest snap position and the second closest snap
+  // position is still larger than the snapport size.
+  // See https://drafts.csswg.org/css-scroll-snap-1/#snap-overflow
+  //
+  // Note: This range contains scroll-margin values.
+  CopyableTArray<ScrollSnapRange> mXRangeWiderThanSnapport;
+  CopyableTArray<ScrollSnapRange> mYRangeWiderThanSnapport;
+
+  // Note: This snapport size has been already deflated by scroll-padding.
+  nsSize mSnapportSize;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_layout_ScrollSnapInfo_h_