QTextCursor: Use RasterOp_NotDestination composition mode for drawing the cursor

This has several advantages over the current “fill the rectangle with the
default text color” approach:

- When the background color for some block of text is black, the cursor will be
  white and visible.

- It is possible to set the cursor width to width of a character (for example
  for monospace edits), and the characters will be visible when the cursor is
  displayed.

Change-Id: I2e6303166d5d63c8dd11ec4fcf3d734cdf440e7e
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index 5778e1818b..e2939785b2 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -1326,7 +1326,11 @@ void QTextLayout::drawCursor(QPainter *p, const QPointF &pos, int cursorPosition
                               && (p->transform().type() > QTransform::TxTranslate);
     if (toggleAntialiasing)
         p->setRenderHint(QPainter::Antialiasing);
+    QPainter::CompositionMode origCompositionMode = p->compositionMode();
+    if (p->paintEngine()->hasFeature(QPaintEngine::RasterOpModes))
+        p->setCompositionMode(QPainter::RasterOp_NotDestination);
     p->fillRect(QRectF(x, y, qreal(width), (base + descent).toReal()), p->pen().brush());
+    p->setCompositionMode(origCompositionMode);
     if (toggleAntialiasing)
         p->setRenderHint(QPainter::Antialiasing, false);
     if (d->layoutData->hasBidi) {