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..6f6bba9383717aaa2a252767b2a14f31756f0543 100644
--- a/Source/core/editing/GranularityStrategy.cpp
+++ b/Source/core/editing/GranularityStrategy.cpp
@@ -5,6 +5,7 @@
 #include "config.h"
 #include "core/editing/GranularityStrategy.h"
 
+#include "core/editing/FrameSelection.h"
 #include "core/editing/htmlediting.h"
 
 namespace blink {
@@ -24,14 +25,19 @@ 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() { }
 
@@ -42,10 +48,24 @@ SelectionStrategy DirectionGranularityStrategy::GetType() const
 
 void DirectionGranularityStrategy::Clear()
 {
+    m_state = StrategyState::Cleared;
     m_granularity = CharacterGranularity;
-    m_lastMoveShrunkSelection = false;
+    m_offset = 0;
+    m_extentPoint.zero();
 }
 
+bool DirectionGranularityStrategy::arePositionsInOrder(
+    const VisiblePosition& pos1,
+    const VisiblePosition& pos2,
+    int order)
+{
+    int positionOrder = comparePositions(pos1, pos2);
+    if (order == 0)
+        return positionOrder == 0;
+    return order > 0 ? positionOrder > 0 : positionOrder < 0;
+}
+
+
 VisiblePosition DirectionGranularityStrategy::nextWordBound(
     const VisiblePosition& pos,
     SearchDirection direction,
@@ -60,68 +80,118 @@ VisiblePosition DirectionGranularityStrategy::nextWordBound(
     return startOfWord(pos, wordSide);
 }
 
-VisibleSelection DirectionGranularityStrategy::updateExtent(const VisiblePosition& extentPosition, const VisibleSelection& selection)
+VisibleSelection DirectionGranularityStrategy::updateExtent(const IntPoint& extentPoint, LocalFrame* frame)
 {
-    if (extentPosition == selection.visibleExtent())
-        return selection;
+    const VisibleSelection& selection = frame->selection().selection();
+    // Initialize m_extentPoint if this is the first update after a clear.
+    if (m_state == StrategyState::Cleared) {
+        VisiblePosition pos =  selection.isBaseFirst() ? selection.visibleEnd() : selection.visibleStart();
+        m_extentPoint = IntPoint(pos.absoluteCaretBounds().x(), pos.absoluteCaretBounds().y());
+        m_state = StrategyState::Expanding;
+    }
+
+    IntPoint oldOffsetExtentPoint(m_extentPoint.x() + m_offset, m_extentPoint.y());
+    VisiblePosition oldOffsetExtentPosition = visiblePositionForContentsPoint(oldOffsetExtentPoint, frame);
+
+    // Apply the offset.
+    IntPoint offsetExtentPoint = extentPoint;
+    int dx = extentPoint.x() - m_extentPoint.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);
+        offsetExtentPoint.move(m_offset, 0);
+    }
+    m_extentPoint = extentPoint;
+
+    VisiblePosition offsetExtentPosition = visiblePositionForContentsPoint(offsetExtentPoint, frame);
+
+    // Reset the offset in case of a line change. Also reset it if we detect a y
+    // component to the vector between the old and the new positions which would
+    // happen if the text is rotated. The offset feature doesn't work for
+    // non-horizontal text.
+    if (!inSameLine(offsetExtentPosition, oldOffsetExtentPosition)
+        || (offsetExtentPosition.absoluteCaretBounds().maxY() - oldOffsetExtentPosition.absoluteCaretBounds().maxY()) != 0) {
+        m_offset = 0;
+        offsetExtentPoint = extentPoint;
+        offsetExtentPosition = visiblePositionForContentsPoint(extentPoint, frame);
+    }
 
     const VisiblePosition base = selection.visibleBase();
-    const VisiblePosition oldExtentWithGranularity = selection.isBaseFirst() ? selection.visibleEnd() : selection.visibleStart();
+    int extentBaseOrder = comparePositions(offsetExtentPosition, base);
 
-    int extentBaseOrder = comparePositions(extentPosition, base);
-    int oldExtentBaseOrder = comparePositions(oldExtentWithGranularity, base);
+    // Do not allow selection and extent to be at the same position
+    if (extentBaseOrder == 0)
+        return selection;
 
-    bool extentBaseOrderSwitched = (extentBaseOrder > 0 && oldExtentBaseOrder < 0)
-        || (extentBaseOrder < 0 && oldExtentBaseOrder > 0);
+    int oldExtentBaseOrder = comparePositions(selection.visibleExtent(), base);
+    bool extentBaseOrderSwitched = !arePositionsInOrder(offsetExtentPosition, base, oldExtentBaseOrder);
 
     // 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.
+    VisiblePosition currentWordBoundary;
     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 current word boundary in this new direction and
+        // based on the |base| position.
         currentWordBoundary = nextWordBound(
             base,
             extentBaseOrder > 0 ? SearchDirection::SearchForward : SearchDirection::SearchBackwards,
             BoundAdjust::NextBoundIfOnBound);
         m_granularity = CharacterGranularity;
-        // When the base/extent order switches it doesn't count as shrinking selection.
-        thisMoveShrunkSelection = false;
+    } else {
+        // Calculate the current 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.
+        currentWordBoundary = nextWordBound(
+            oldOffsetExtentPosition,
+            selection.isBaseFirst() ? SearchDirection::SearchForward : SearchDirection::SearchBackwards,
+            m_state == StrategyState::Shrinking ? BoundAdjust::NextBoundIfOnBound : BoundAdjust::CurrentPosIfOnBound);
     }
 
-    bool expandedBeyondWordBoundary;
-    if (extentBaseOrder > 0)
-        expandedBeyondWordBoundary = comparePositions(extentPosition, currentWordBoundary) > 0;
-    else
-        expandedBeyondWordBoundary = comparePositions(extentPosition, currentWordBoundary) < 0;
-    if (expandedBeyondWordBoundary) {
+    bool expandedBeyondWordBoundary = arePositionsInOrder(offsetExtentPosition, currentWordBoundary, extentBaseOrder);
+
+    // The selection is shrunk if the extent changes position to be closer to
+    // the base, and the extent/base order wasn't switched.
+    bool thisMoveShrunkSelection =
+        !extentBaseOrderSwitched
+        && oldOffsetExtentPosition != offsetExtentPosition
+        && arePositionsInOrder(oldOffsetExtentPosition, offsetExtentPosition, extentBaseOrder);
+
+    if (expandedBeyondWordBoundary)
         m_granularity = WordGranularity;
-    } else if (thisMoveShrunkSelection) {
+    else if (thisMoveShrunkSelection)
         m_granularity = CharacterGranularity;
-        m_lastMoveShrunkSelection = true;
-    }
 
-    m_lastMoveShrunkSelection = thisMoveShrunkSelection;
-    VisibleSelection newSelection = selection;
-    newSelection.setExtent(extentPosition);
+    VisiblePosition newSelectionExtent = offsetExtentPosition;
     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(offsetExtentPosition, SearchDirection::SearchBackwards, BoundAdjust::CurrentPosIfOnBound);
+        VisiblePosition boundAfterExtent = nextWordBound(offsetExtentPosition, SearchDirection::SearchForward, BoundAdjust::CurrentPosIfOnBound);
+        int xMiddleBetweenBounds = (boundAfterExtent.absoluteCaretBounds().x() + boundBeforeExtent.absoluteCaretBounds().x()) / 2;
+        bool extentBeforeMiddle = offsetExtentPoint.x() < xMiddleBetweenBounds;
+
+        newSelectionExtent = extentBeforeMiddle ? boundBeforeExtent : boundAfterExtent;
+        // Update the offset if needed.
+        if (!inSameLine(newSelectionExtent, selection.visibleExtent()))
+            m_offset = 0;
+        else if ((extentBaseOrder > 0 && !extentBeforeMiddle) || (extentBaseOrder < 0 && extentBeforeMiddle))
+            m_offset = newSelectionExtent.absoluteCaretBounds().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;
+
+    VisibleSelection newSelection = selection;
+    newSelection.setExtent(newSelectionExtent);
     return newSelection;
 }