litehtml: Fix selection artifacts with scaled view

If you zoom into a page (Ctrl-+) and then select, artifacts could be
left behind when dragging or removing the selection again.
Fiddle around with coordinate transformations (with regard to rounding)
to fix that.

Change-Id: I68c29d8e3559b90dbb3b93550338e483d14731bf
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/help/qlitehtml/container_qpainter.cpp

@@ -998,8 +998,9 @@ QVector<QRect> DocumentContainer::mouseMoveEvent(const QPoint &documentPos,
                                                                   viewportPos,
                                                                   m_selection.mode);
         if (element.element) {
+            redrawRects.append(
+                m_selection.boundingRect() /*.adjusted(-1, -1, +1, +1)*/); // redraw old selection area
             m_selection.endElem = element;
-            redrawRects.append(m_selection.boundingRect()); // redraw old selection area
             m_selection.update();
             redrawRects.append(m_selection.boundingRect());
         }

src/plugins/help/qlitehtml/qlitehtmlwidget.cpp

@@ -664,21 +664,11 @@ QPoint QLiteHtmlWidget::toVirtual(const QPoint &p) const
     return {int(p.x() / d->zoomFactor), int(p.y() / d->zoomFactor)};
 }
 
-QPoint QLiteHtmlWidget::fromVirtual(const QPoint &p) const
-{
-    return {int(p.x() * d->zoomFactor), int(p.y() * d->zoomFactor)};
-}
-
 QSize QLiteHtmlWidget::toVirtual(const QSize &s) const
 {
     return {int(s.width() / d->zoomFactor), int(s.height() / d->zoomFactor)};
 }
 
-QSize QLiteHtmlWidget::fromVirtual(const QSize &s) const
-{
-    return {int(s.width() * d->zoomFactor + 0.5), int(s.height() * d->zoomFactor + 0.5)};
-}
-
 QRect QLiteHtmlWidget::toVirtual(const QRect &r) const
 {
     return {toVirtual(r.topLeft()), toVirtual(r.size())};
@@ -686,5 +676,9 @@ QRect QLiteHtmlWidget::toVirtual(const QRect &r) const
 
 QRect QLiteHtmlWidget::fromVirtual(const QRect &r) const
 {
-    return {fromVirtual(r.topLeft()), fromVirtual(r.size())};
+    const QPoint tl{int(r.x() * d->zoomFactor), int(r.y() * d->zoomFactor)};
+    // round size up, and add one since the topleft point was rounded down
+    const QSize s{int(r.width() * d->zoomFactor + 0.5) + 1,
+                  int(r.height() * d->zoomFactor + 0.5) + 1};
+    return {tl, s};
 }

src/plugins/help/qlitehtml/qlitehtmlwidget.h

@@ -82,9 +82,7 @@ private:
     QPoint scrollPosition() const;
     void htmlPos(const QPoint &pos, QPoint *viewportPos, QPoint *htmlPos) const;
     QPoint toVirtual(const QPoint &p) const;
-    QPoint fromVirtual(const QPoint &p) const;
     QSize toVirtual(const QSize &s) const;
-    QSize fromVirtual(const QSize &s) const;
     QRect toVirtual(const QRect &r) const;
     QRect fromVirtual(const QRect &r) const;