Improving direction-based selection strategy.

Source/core/editing/GranularityStrategy.cpp

Index: Source/core/editing/GranularityStrategy.cpp
diff --git a/Source/core/editing/GranularityStrategy.cpp b/Source/core/editing/GranularityStrategy.cpp
index 5a5fd9ee30330abf12efdd949c68fff152dc0636..3ab12fc44c013a830b42a50861f6cef9e76aafbe 100644
--- a/Source/core/editing/GranularityStrategy.cpp
+++ b/Source/core/editing/GranularityStrategy.cpp
@@ -5,10 +5,53 @@
 #include "config.h"
 #include "core/editing/GranularityStrategy.h"
 
+#include "core/editing/FrameSelection.h"
 #include "core/editing/htmlediting.h"
 
 namespace blink {
 
+enum class BoundAdjust {CurrentPosIfOnBound, NextBoundIfOnBound};
+enum class SearchDirection {SearchBackwards, SearchForward};
+
+// We use the bottom-left corner of the caret rect to represent the
+// location of a VisiblePosition. This way locations corresponding to
+// VisiblePositions on the same line will all have the same y coordinate
+// unless the text is transformed.
+static IntPoint positionLocation(const VisiblePosition& vp)
+{
+    return vp.absoluteCaretBounds().minXMaxYCorner();
+}
+
+// Order is specified using the same contract as comparePositions.
+static bool arePositionsInSpecifiedOrder(
+    const VisiblePosition& vp1,
+    const VisiblePosition& vp2,
+    int specifiedOrder)
+{
+    int positionOrder = comparePositions(vp1, vp2);
+    if (specifiedOrder == 0)
+        return positionOrder == 0;
+    return specifiedOrder > 0 ? positionOrder > 0 : positionOrder < 0;
+}
+
+// Returns the next word boundary starting from |pos|. |direction| specifies
+// the direction in which to search for the next bound. nextIfOnBound
+// controls whether |pos| or the next boundary is returned when |pos| is
+// located exactly on word boundary.
+static VisiblePosition nextWordBound(
+    const VisiblePosition& pos,
+    SearchDirection direction,
+    BoundAdjust wordBoundAdjust)
+{
+    bool nextBoundIfOnBound = wordBoundAdjust ==  BoundAdjust::NextBoundIfOnBound;
+    if (direction == SearchDirection::SearchForward) {
+        EWordSide wordSide = nextBoundIfOnBound ? RightWordIfOnBoundary : LeftWordIfOnBoundary;
+        return endOfWord(pos, wordSide);
+    }
+    EWordSide wordSide = nextBoundIfOnBound ? LeftWordIfOnBoundary : RightWordIfOnBoundary;
+    return startOfWord(pos, wordSide);
+}
+
 GranularityStrategy::GranularityStrategy() { }
 
 GranularityStrategy::~GranularityStrategy() { }
@@ -24,14 +67,19 @@ SelectionStrategy CharacterGranularityStrategy::GetType() const
 
 void CharacterGranularityStrategy::Clear() { };
 
-VisibleSelection CharacterGranularityStrategy::updateExtent(const VisiblePosition& extentPosition, const VisibleSelection& selection)
+VisibleSelection CharacterGranularityStrategy::updateExtent(const IntPoint& extentPoint, LocalFrame* frame)
 {
+    const VisiblePosition& extentPosition = visiblePositionForContentsPoint(extentPoint, frame);
+    const VisibleSelection& selection = frame->selection().selection();
+    if (selection.visibleBase() == extentPosition)
+        return selection;
     return VisibleSelection(selection.visibleBase(), extentPosition);
 }
 
 DirectionGranularityStrategy::DirectionGranularityStrategy()
-    : m_granularity(CharacterGranularity)
-    , m_lastMoveShrunkSelection(false) { }
+    : m_state(StrategyState::Cleared)
+    , m_granularity(CharacterGranularity)
+    , m_offset(0) { }
 
 DirectionGranularityStrategy::~DirectionGranularityStrategy() { }
 
@@ -42,86 +90,149 @@ SelectionStrategy DirectionGranularityStrategy::GetType() const
 
 void DirectionGranularityStrategy::Clear()
 {
+    m_state = StrategyState::Cleared;
     m_granularity = CharacterGranularity;
-    m_lastMoveShrunkSelection = false;
+    m_offset = 0;
+    m_diffExtentPointFromExtentPosition = IntSize();
 }
 
-VisiblePosition DirectionGranularityStrategy::nextWordBound(
-    const VisiblePosition& pos,
-    SearchDirection direction,
-    BoundAdjust wordBoundAdjust)
+VisibleSelection DirectionGranularityStrategy::updateExtent(const IntPoint& extentPoint, LocalFrame* frame)
 {
-    bool nextBoundIfOnBound = wordBoundAdjust ==  BoundAdjust::NextBoundIfOnBound;
-    if (direction == SearchDirection::SearchForward) {
-        EWordSide wordSide = nextBoundIfOnBound ? RightWordIfOnBoundary : LeftWordIfOnBoundary;
-        return endOfWord(pos, wordSide);
+    const VisibleSelection& selection = frame->selection().selection();
+
+    if (m_state == StrategyState::Cleared)
+        m_state = StrategyState::Expanding;
+
+    VisiblePosition oldOffsetExtentPosition = selection.visibleExtent();
+    IntPoint oldExtentLocation = positionLocation(oldOffsetExtentPosition);
+
+    IntPoint oldOffsetExtentPoint = oldExtentLocation + m_diffExtentPointFromExtentPosition;
+    IntPoint oldExtentPoint = IntPoint(oldOffsetExtentPoint.x() - m_offset, oldOffsetExtentPoint.y());
+
+    // Apply the offset.
+    IntPoint newOffsetExtentPoint = extentPoint;
+    int dx = extentPoint.x() - oldExtentPoint.x();
+    if (m_offset != 0) {
+        if (m_offset > 0 && dx > 0)
+            m_offset = std::max(0, m_offset - dx);
+        else if (m_offset < 0 && dx < 0)
+            m_offset = std::min(0, m_offset - dx);
+        newOffsetExtentPoint.move(m_offset, 0);
     }
-    EWordSide wordSide = nextBoundIfOnBound ? LeftWordIfOnBoundary : RightWordIfOnBoundary;
-    return startOfWord(pos, wordSide);
-}
 
-VisibleSelection DirectionGranularityStrategy::updateExtent(const VisiblePosition& extentPosition, const VisibleSelection& selection)
-{
-    if (extentPosition == selection.visibleExtent())
-        return selection;
+    VisiblePosition newOffsetExtentPosition = visiblePositionForContentsPoint(newOffsetExtentPoint, frame);
+    IntPoint newOffsetLocation = positionLocation(newOffsetExtentPosition);
 
-    const VisiblePosition base = selection.visibleBase();
-    const VisiblePosition oldExtentWithGranularity = selection.isBaseFirst() ? selection.visibleEnd() : selection.visibleStart();
-
-    int extentBaseOrder = comparePositions(extentPosition, base);
-    int oldExtentBaseOrder = comparePositions(oldExtentWithGranularity, base);
-
-    bool extentBaseOrderSwitched = (extentBaseOrder > 0 && oldExtentBaseOrder < 0)
-        || (extentBaseOrder < 0 && oldExtentBaseOrder > 0);
-
-    // Determine the boundary of the 'current word', i.e. the boundary extending
-    // beyond which should change the granularity to WordGranularity.
-    // If the last move has shrunk the selection and is now exactly on the word
-    // boundary - we need to take the next bound as the bound of the "current
-    // word".
-    VisiblePosition currentWordBoundary = nextWordBound(
-        oldExtentWithGranularity,
-        oldExtentBaseOrder > 0 ? SearchDirection::SearchForward : SearchDirection::SearchBackwards,
-        m_lastMoveShrunkSelection ? BoundAdjust::NextBoundIfOnBound : BoundAdjust::CurrentPosIfOnBound);
-
-    bool thisMoveShrunkSelection = (extentBaseOrder > 0 && comparePositions(extentPosition, selection.visibleExtent()) < 0)
-        || (extentBaseOrder < 0 && comparePositions(extentPosition, selection.visibleExtent()) > 0);
-    // If the extent-base order was switched, then the selection is now
-    // expanding in a different direction than before. Therefore we need to
-    // calculate the boundary of the 'current word' in this new direction in
-    // order to be able to tell if the selection expanded beyond it.
-    if (extentBaseOrderSwitched) {
-        currentWordBoundary = nextWordBound(
-            base,
-            extentBaseOrder > 0 ? SearchDirection::SearchForward : SearchDirection::SearchBackwards,
-            BoundAdjust::NextBoundIfOnBound);
+    // Reset the offset in case of a vertical change in the location (could be
+    // due to a line change or due to an unusual layout, e.g. rotated text).
+    bool verticalChange = newOffsetLocation.y() != oldExtentLocation.y();
+    if (verticalChange) {
+        m_offset = 0;
         m_granularity = CharacterGranularity;
-        // When the base/extent order switches it doesn't count as shrinking selection.
-        thisMoveShrunkSelection = false;
+        newOffsetExtentPoint = extentPoint;
+        newOffsetExtentPosition = visiblePositionForContentsPoint(extentPoint, frame);
     }
 
-    bool expandedBeyondWordBoundary;
-    if (extentBaseOrder > 0)
-        expandedBeyondWordBoundary = comparePositions(extentPosition, currentWordBoundary) > 0;
-    else
-        expandedBeyondWordBoundary = comparePositions(extentPosition, currentWordBoundary) < 0;
-    if (expandedBeyondWordBoundary) {
-        m_granularity = WordGranularity;
-    } else if (thisMoveShrunkSelection) {
-        m_granularity = CharacterGranularity;
-        m_lastMoveShrunkSelection = true;
+    const VisiblePosition base = selection.visibleBase();
+
+    // Do not allow empty selection.
+    if (newOffsetExtentPosition == base)
+        return selection;
+
+    // The direction granularity strategy, particularly the "offset" feature
+    // doesn't work with non-horizontal text (e.g. when the text is rotated).
+    // So revert to the behavior equivalent to the character granularity
+    // strategy if we detect that the text's baseline coordinate changed
+    // without a line change.
+    if (verticalChange && inSameLine(newOffsetExtentPosition, oldOffsetExtentPosition))
+        return VisibleSelection(selection.visibleBase(), newOffsetExtentPosition);
+
+    int oldExtentBaseOrder = selection.isBaseFirst() ? 1 : -1;
+
+    int newExtentBaseOrder;
+    bool thisMoveShrunkSelection;
+    if (newOffsetExtentPosition == oldOffsetExtentPosition) {
+        if (m_granularity == CharacterGranularity)
+            return selection;
+
+        // If we are in Word granularity, we cannot exit here, since we may pass
+        // the middle of the word without changing the position (in which case
+        // the selection needs to expand).
+        thisMoveShrunkSelection = false;
+        newExtentBaseOrder = oldExtentBaseOrder;
+    } else {
+        bool selectionExpanded = arePositionsInSpecifiedOrder(newOffsetExtentPosition, oldOffsetExtentPosition, oldExtentBaseOrder);
+        bool extentBaseOrderSwitched = selectionExpanded ? false : !arePositionsInSpecifiedOrder(newOffsetExtentPosition, base, oldExtentBaseOrder);
+        newExtentBaseOrder = extentBaseOrderSwitched ? -oldExtentBaseOrder : oldExtentBaseOrder;
+
+        // Determine the word boundary, i.e. the boundary extending beyond which
+        // should change the granularity to WordGranularity.
+        VisiblePosition wordBoundary;
+        if (extentBaseOrderSwitched) {
+            // Special case.
+            // If the extent-base order was switched, then the selection is now
+            // expanding in a different direction than before. Therefore we
+            // calculate the word boundary in this new direction and based on
+            // the |base| position.
+            wordBoundary = nextWordBound(
+                base,
+                newExtentBaseOrder > 0 ? SearchDirection::SearchForward : SearchDirection::SearchBackwards,
+                BoundAdjust::NextBoundIfOnBound);
+            m_granularity = CharacterGranularity;
+        } else {
+            // Calculate the word boundary based on |oldExtentWithGranularity|.
+            // If selection was shrunk in the last update and the extent is now
+            // exactly on the word boundary - we need to take the next bound as
+            // the bound of the current word.
+            wordBoundary = nextWordBound(
+                oldOffsetExtentPosition,
+                oldExtentBaseOrder > 0 ? SearchDirection::SearchForward : SearchDirection::SearchBackwards,
+                m_state == StrategyState::Shrinking ? BoundAdjust::NextBoundIfOnBound : BoundAdjust::CurrentPosIfOnBound);
+        }
+
+        bool expandedBeyondWordBoundary;
+        if (selectionExpanded)
+            expandedBeyondWordBoundary = arePositionsInSpecifiedOrder(newOffsetExtentPosition, wordBoundary, newExtentBaseOrder);
+        else if (extentBaseOrderSwitched)
+            expandedBeyondWordBoundary = arePositionsInSpecifiedOrder(newOffsetExtentPosition, wordBoundary, newExtentBaseOrder);
+        else
+            expandedBeyondWordBoundary = false;
+
+        // The selection is shrunk if the extent changes position to be closer to
+        // the base, and the extent/base order wasn't switched.
+        thisMoveShrunkSelection = !extentBaseOrderSwitched && !selectionExpanded;
+
+        if (expandedBeyondWordBoundary)
+            m_granularity = WordGranularity;
+        else if (thisMoveShrunkSelection)
+            m_granularity = CharacterGranularity;
     }
 
-    m_lastMoveShrunkSelection = thisMoveShrunkSelection;
-    VisibleSelection newSelection = selection;
-    newSelection.setExtent(extentPosition);
+    VisiblePosition newSelectionExtent = newOffsetExtentPosition;
     if (m_granularity == WordGranularity) {
-        if (extentBaseOrder > 0)
-            newSelection.setEndRespectingGranularity(m_granularity, LeftWordIfOnBoundary);
-        else
-            newSelection.setStartRespectingGranularity(m_granularity, RightWordIfOnBoundary);
+        // Determine the bounds of the word where the extent is located.
+        // Set the selection extent to one of the two bounds depending on
+        // whether the extent is passed the middle of the word.
+        VisiblePosition boundBeforeExtent = nextWordBound(newOffsetExtentPosition, SearchDirection::SearchBackwards, BoundAdjust::CurrentPosIfOnBound);
+        VisiblePosition boundAfterExtent = nextWordBound(newOffsetExtentPosition, SearchDirection::SearchForward, BoundAdjust::CurrentPosIfOnBound);
+        int xMiddleBetweenBounds = (positionLocation(boundAfterExtent).x() + positionLocation(boundBeforeExtent).x()) / 2;
+        bool offsetExtentBeforeMiddle = newOffsetExtentPoint.x() < xMiddleBetweenBounds;
+        newSelectionExtent = offsetExtentBeforeMiddle ? boundBeforeExtent : boundAfterExtent;
+        // Update the offset if selection expanded in word granularity.
+        if (newSelectionExtent != selection.visibleExtent()
+            && ((newExtentBaseOrder > 0 && !offsetExtentBeforeMiddle) || (newExtentBaseOrder < 0 && offsetExtentBeforeMiddle))) {
+            m_offset = positionLocation(newSelectionExtent).x() - extentPoint.x();
+        }
     }
 
+    // Only update the state if the selection actually changed as a result of
+    // this move.
+    if (newSelectionExtent != selection.visibleExtent())
+        m_state = thisMoveShrunkSelection ? StrategyState::Shrinking : StrategyState::Expanding;
+
+    m_diffExtentPointFromExtentPosition = extentPoint + IntSize(m_offset, 0) - positionLocation(newSelectionExtent);
+    VisibleSelection newSelection = selection;
+    newSelection.setExtent(newSelectionExtent);
     return newSelection;
 }