cabana: fix chart background issue in live mode (#27793)

* fix background

* Update tools/cabana/chartswidget.cc

---------

Co-authored-by: Shane Smiskol <shane@smiskol.com>
old-commit-hash: ea91532ac1

tools/cabana/chartswidget.cc

@@ -358,6 +358,7 @@ bool ChartsWidget::event(QEvent *event) {
     case QEvent::WindowDeactivate:
     case QEvent::FocusIn:
     case QEvent::FocusOut:
+    case QEvent::Leave:
       showValueTip(-1);
       break;
     default:
@@ -618,7 +619,7 @@ void ChartView::updateSeries(const cabana::Signal *sig) {
     }
   }
   updateAxisY();
-  resetChartCache();
+  chart_pixmap = QPixmap();
 }
 
 // auto zoom on yaxis
@@ -874,9 +875,9 @@ void ChartView::paintEvent(QPaintEvent *event) {
       const qreal dpr = viewport()->devicePixelRatioF();
       chart_pixmap = QPixmap(viewport()->size() * dpr);
       chart_pixmap.setDevicePixelRatio(dpr);
-      chart_pixmap.fill(palette().color(QPalette::Base));
       QPainter p(&chart_pixmap);
       p.setRenderHints(QPainter::Antialiasing);
+      drawBackground(&p, viewport()->rect());
       scene()->setSceneRect(viewport()->rect());
       scene()->render(&p);
     }
@@ -891,6 +892,10 @@ void ChartView::paintEvent(QPaintEvent *event) {
   }
 }
 
+void ChartView::drawBackground(QPainter *painter, const QRectF &rect) {
+  painter->fillRect(rect, palette().color(QPalette::Base));
+}
+
 void ChartView::drawForeground(QPainter *painter, const QRectF &rect) {
   // draw time line
   qreal x = chart()->mapToPosition(QPointF{cur_sec, 0}).x();

tools/cabana/chartswidget.h

@@ -91,6 +91,7 @@ private:
   void resetChartCache();
   void paintEvent(QPaintEvent *event) override;
   void drawForeground(QPainter *painter, const QRectF &rect) override;
+  void drawBackground(QPainter *painter, const QRectF &rect) override;
   std::tuple<double, double, int> getNiceAxisNumbers(qreal min, qreal max, int tick_count);
   qreal niceNumber(qreal x, bool ceiling);
   QXYSeries *createSeries(SeriesType type, QColor color);