1 files changed, 105 insertions, 0 deletions
diff --git a/layout/generic/ScrollSnapInfo.cpp b/layout/generic/ScrollSnapInfo.cpp
new file mode 100644
index 0000000000..7f9f410c33
--- /dev/null
+++ b/layout/generic/ScrollSnapInfo.cpp
@@ -0,0 +1,105 @@
+/* -*- 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/. */
+
+#include "ScrollSnapInfo.h"
+
+#include "nsPoint.h"
+#include "nsRect.h"
+#include "nsStyleStruct.h"
+#include "mozilla/WritingModes.h"
+
+namespace mozilla {
+
+ScrollSnapInfo::ScrollSnapInfo()
+    : mScrollSnapStrictnessX(StyleScrollSnapStrictness::None),
+      mScrollSnapStrictnessY(StyleScrollSnapStrictness::None) {}
+
+bool ScrollSnapInfo::HasScrollSnapping() const {
+  return mScrollSnapStrictnessY != StyleScrollSnapStrictness::None ||
+         mScrollSnapStrictnessX != StyleScrollSnapStrictness::None;
+}
+
+bool ScrollSnapInfo::HasSnapPositions() const {
+  if (!HasScrollSnapping()) {
+    return false;
+  }
+
+  for (const auto& target : mSnapTargets) {
+    if ((target.mSnapPoint.mX &&
+         mScrollSnapStrictnessX != StyleScrollSnapStrictness::None) ||
+        (target.mSnapPoint.mY &&
+         mScrollSnapStrictnessY != StyleScrollSnapStrictness::None)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void ScrollSnapInfo::InitializeScrollSnapStrictness(
+    WritingMode aWritingMode, const nsStyleDisplay* aDisplay) {
+  if (aDisplay->mScrollSnapType.strictness == StyleScrollSnapStrictness::None) {
+    return;
+  }
+
+  mScrollSnapStrictnessX = StyleScrollSnapStrictness::None;
+  mScrollSnapStrictnessY = StyleScrollSnapStrictness::None;
+
+  switch (aDisplay->mScrollSnapType.axis) {
+    case StyleScrollSnapAxis::X:
+      mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      break;
+    case StyleScrollSnapAxis::Y:
+      mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      break;
+    case StyleScrollSnapAxis::Block:
+      if (aWritingMode.IsVertical()) {
+        mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      } else {
+        mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      }
+      break;
+    case StyleScrollSnapAxis::Inline:
+      if (aWritingMode.IsVertical()) {
+        mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      } else {
+        mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      }
+      break;
+    case StyleScrollSnapAxis::Both:
+      mScrollSnapStrictnessX = aDisplay->mScrollSnapType.strictness;
+      mScrollSnapStrictnessY = aDisplay->mScrollSnapType.strictness;
+      break;
+  }
+}
+
+void ScrollSnapInfo::ForEachValidTargetFor(
+    const nsPoint& aDestination,
+    const std::function<bool(const SnapTarget&)>& aFunc) const {
+  for (const auto& target : mSnapTargets) {
+    nsPoint snapPoint(
+        mScrollSnapStrictnessX != StyleScrollSnapStrictness::None &&
+                target.mSnapPoint.mX
+            ? *target.mSnapPoint.mX
+            : aDestination.x,
+        mScrollSnapStrictnessY != StyleScrollSnapStrictness::None &&
+                target.mSnapPoint.mY
+            ? *target.mSnapPoint.mY
+            : aDestination.y);
+    nsRect snappedPort = nsRect(snapPoint, mSnapportSize);
+    // Ignore snap points if snapping to the point would leave the snap area
+    // outside of the snapport.
+    // https://drafts.csswg.org/css-scroll-snap-1/#snap-scope
+    if (!snappedPort.Intersects(target.mSnapArea)) {
+      continue;
+    }
+
+    if (!aFunc(target)) {
+      break;
+    }
+  }
+}
+
+}  // namespace mozilla