Fixed performance issue with scrolling when using X11 graphics system

Depending on the XRender driver (probably), drawing a short straight
line can take quite a while when this line is transparent. On my
laptop's onboard ATI card, this meant that scrolling was unusably slow
when this transparent line was being drawn.

Fixed by avoiding the issue, since there is no actual need to use
transparency here. We can calculate the resulting color in advance
instead.

1 files changed, 11 insertions, 8 deletions

diff --git a/src/plugins/texteditor/basetexteditor.cpp b/src/plugins/texteditor/basetexteditor.cpp
index b9bcb9660d..7825941ea5 100644
--- a/src/plugins/texteditor/basetexteditor.cpp
+++ b/src/plugins/texteditor/basetexteditor.cpp
@@ -1926,6 +1926,13 @@ void BaseTextEditorPrivate::moveCursorVisible(bool ensureVisible)
         q->ensureCursorVisible();
 }
 
+static QColor blendColors(const QColor &a, const QColor &b, int alpha)
+{
+    return QColor((a.red()   * (256 - alpha) + b.red()   * alpha) / 256,
+                  (a.green() * (256 - alpha) + b.green() * alpha) / 256,
+                  (a.blue()  * (256 - alpha) + b.blue()  * alpha) / 256);
+}
+
 static QColor calcBlendColor(const QColor &baseColor, int level, int count)
 {
     QColor color80;
@@ -1960,10 +1967,7 @@ static QColor calcBlendColor(const QColor &baseColor, int level, int count)
 
     const int blendFactor = level * (256 / (count - 2));
 
-    return QColor(
-                (color90.red() * blendFactor + color80.red() * (256 - blendFactor)) / 256,
-                (color90.green() * blendFactor + color80.green() * (256 - blendFactor)) / 256,
-                (color90.blue() * blendFactor + color80.blue() * (256 - blendFactor)) / 256);
+    return blendColors(color80, color90, blendFactor);
 }
 
 void BaseTextEditor::paintEvent(QPaintEvent *e)
@@ -2379,10 +2383,9 @@ void BaseTextEditor::paintEvent(QPaintEvent *e)
 
     if (lineX > 0) {
         const QColor bg = palette().base().color();
-        QColor col = (bg.value() > 128) ? Qt::black : Qt::white;
-        col.setAlpha(32);
-        painter.setPen(QPen(col, 0));
-        painter.drawLine(QPointF(lineX, 0), QPointF(lineX, viewport()->height()));
+        const QColor col = (bg.value() > 128) ? Qt::black : Qt::white;
+        painter.setPen(blendColors(d->m_ifdefedOutFormat.background().color(), col, 32));
+        painter.drawLine(QPointF(lineX, er.top()), QPointF(lineX, er.bottom()));
     }
 }