Fix selection of text with negative right bearing

Selecting text with a negative right bearing (like italic text)
would cause clipping to occur at the edges of the characters.

The algorithm for drawing text and text selection tried to
divide the text into two: 1. Selected text, and 2. Unselected text.
However, the selected text might be drawn outside the selection
rect when it has a negative right bearing. Similarly, unselected
text before the selection might overlap with the selection rect
when it has a negative right bearing, or unselected text after
the selection might overlap if it has a negative left bearing.

See added test textinput_italic_selected.qml for an example.

To rectify this, we do drawing of selected text like this:
1. Draw all text with unselected color
2. Draw selection rects
3. Draw the following in the selection text color and clipped
   to the selection rect:
     A. The selected text
     B. The unselected text right before the selection
     C. The unselected text right after the selection

To avoid drawing the same text twice for extra boldness,
we check if 3B or 3C actually contain 3A, in which case we skip
3A.

[ChangeLog][Text] Fixed clipping when selecting text with negative
right bearing.

Task-number: QTBUG-34233
Change-Id: I3506b3a72a2d963c5f24c5b819bbb92769b9aee1
Reviewed-by: Samuel Nevala <samuel.nevala@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/quick/items/qquicktextnodeengine_p.h b/src/quick/items/qquicktextnodeengine_p.h
index 9a64853dd3..142375b5a3 100644
--- a/src/quick/items/qquicktextnodeengine_p.h
+++ b/src/quick/items/qquicktextnodeengine_p.h
@@ -75,10 +75,11 @@ public:
 
         BinaryTreeNode(const QGlyphRun &g, SelectionState selState, const QRectF &brect,
                        const QQuickTextNode::Decorations &decs, const QColor &c, const QColor &bc,
-                       const QPointF &pos, qreal a)
+                       const QPointF &pos, qreal a, int rangeStart, int rangeEnd)
             : glyphRun(g), boundingRect(brect), selectionState(selState), clipNode(0), decorations(decs)
             , color(c), backgroundColor(bc), position(pos), ascent(a), leftChildIndex(-1), rightChildIndex(-1)
         {
+            ranges.append(qMakePair(rangeStart, rangeEnd));
         }
 
         QGlyphRun glyphRun;
@@ -95,11 +96,14 @@ public:
         int leftChildIndex;
         int rightChildIndex;
 
+        QList<QPair<int, int> > ranges;
+
         static void insert(QVarLengthArray<BinaryTreeNode, 16> *binaryTree, const QRectF &rect, const QImage &image, qreal ascent, SelectionState selectionState)
         { insert(binaryTree, BinaryTreeNode(rect, image, selectionState, ascent)); }
 
         static void insert(QVarLengthArray<BinaryTreeNode, 16> *binaryTree, const QGlyphRun &glyphRun, SelectionState selectionState,
-                           QQuickTextNode::Decorations decorations, const QColor &textColor, const QColor &backgroundColor, const QPointF &position);
+                           QQuickTextNode::Decorations decorations, const QColor &textColor, const QColor &backgroundColor, const QPointF &position,
+                           int rangeStart, int rangeEnd);
         static void insert(QVarLengthArray<BinaryTreeNode, 16> *binaryTree, const BinaryTreeNode &binaryTreeNode);
         static void inOrder(const QVarLengthArray<BinaryTreeNode, 16> &binaryTree, QVarLengthArray<int> *sortedIndexes, int currentIndex = 0);
     };
@@ -134,8 +138,8 @@ public:
                        SelectionState selectionState,
                        QTextDocument *textDocument, int pos,
                        QTextFrameFormat::Position layoutPosition = QTextFrameFormat::InFlow);
-    void addSelectedGlyphs(const QGlyphRun &glyphRun);
-    void addUnselectedGlyphs(const QGlyphRun &glyphRun);
+    void addSelectedGlyphs(const QGlyphRun &glyphRun, int rangeStart, int rangeEnd);
+    void addUnselectedGlyphs(const QGlyphRun &glyphRun, int rangeStart, int rangeEnd);
     void addGlyphsInRange(int rangeStart, int rangeEnd,
                           const QColor &color, const QColor &backgroundColor,
                           int selectionStart, int selectionEnd);