Improve rendering of the rounded borders

All corners should be round if not maximized. This is now done by
setting better clip regions to restrict the rendering to the
currently relevant area. So we don't render the background behind
the title area, instead the title area also renders a rounded rect.

windec/kdecoration2/breezedeco.cpp

@@ -181,9 +181,13 @@ void Decoration::paint(QPainter *painter)
     painter->fillRect(rect(), Qt::transparent);
     painter->save();
     painter->setRenderHint(QPainter::Antialiasing);
-    painter->setPen(m_colorSettings.frame(client()->isActive()));
+    painter->setPen(Qt::NoPen);
     painter->setBrush(m_colorSettings.frame(client()->isActive()));
+    // clip away the top part
+    painter->save();
+    painter->setClipRect(0, borderTop(), size().width(), size().height() - borderTop(), Qt::IntersectClip);
     painter->drawRoundedRect(rect(), 5.0, 5.0);
+    painter->restore();
 
     paintTitleBar(painter);
 
@@ -202,7 +206,18 @@ void Decoration::paintTitleBar(QPainter *painter)
     gradient.setColorAt(0.0, titleBarColor.lighter(client()->isActive() ? 120.0 : 100.0));
     gradient.setColorAt(0.8, titleBarColor);
     gradient.setColorAt(1.0, titleBarColor);
-    painter->fillRect(titleRect, gradient);
+    gradient.setFinalStop(0.0, titleRect.height());
+    painter->save();
+    painter->setBrush(gradient);
+    painter->setPen(Qt::NoPen);
+    if (client()->isMaximized()) {
+        painter->drawRect(titleRect);
+    } else {
+        painter->setClipRect(titleRect, Qt::IntersectClip);
+        // we make the rect a little bit larger to be able to clip away the rounded corners on bottom
+        painter->drawRoundedRect(titleRect.adjusted(0, 0, 0, 5), 5.0, 5.0);
+    }
+    painter->restore();
     const int titleBarSpacer = KDecoration2::DecorationSettings::self()->smallSpacing();
     if (true) {
         // TODO: should be config option
@@ -217,6 +232,7 @@ void Decoration::paintTitleBar(QPainter *painter)
     painter->setFont(KDecoration2::DecorationSettings::self()->font());
     const QRect cR = captionRect();
     const QString caption = painter->fontMetrics().elidedText(client()->caption(), Qt::ElideMiddle, cR.width());
+    painter->setPen(m_colorSettings.frame(client()->isActive()));
     painter->drawText(cR, Qt::AlignCenter | Qt::TextSingleLine, caption);
 
     // draw all buttons