cabana: dynamically switch between OpenGL (#27167)

* cabana: dynamically switch between OpenGL

* put back todo

* only switch when x axis changes

tools/cabana/chartswidget.cc

@@ -358,11 +358,6 @@ void ChartView::setPlotAreaLeftPosition(int pos) {
 void ChartView::addSeries(const QString &msg_id, const Signal *sig) {
   QLineSeries *series = new QLineSeries(this);
 
-  // TODO: Due to a bug in CameraWidget the camera frames
-  // are drawn instead of the graphs on MacOS. Re-enable OpenGL when fixed
-#ifndef __APPLE__
-  series->setUseOpenGL(true);
-#endif
   chart()->addSeries(series);
   series->attachAxis(axis_x);
   series->attachAxis(axis_y);
@@ -476,17 +471,32 @@ void ChartView::updatePlot(double cur, double min, double max) {
   if (min != axis_x->min() || max != axis_x->max()) {
     axis_x->setRange(min, max);
     updateAxisY();
-  }
 
-  // Show points when zoomed in enough
-  for (auto &s : sigs) {
-    auto begin = std::lower_bound(s.vals.begin(), s.vals.end(), axis_x->min(), [](auto &p, double x) { return p.x() < x; });
-    auto end = std::lower_bound(s.vals.begin(), s.vals.end(), axis_x->max(), [](auto &p, double x) { return p.x() < x; });
+    // Show points when zoomed in enough
+    for (auto &s : sigs) {
+      auto begin = std::lower_bound(s.vals.begin(), s.vals.end(), axis_x->min(), [](auto &p, double x) { return p.x() < x; });
+      auto end = std::lower_bound(s.vals.begin(), s.vals.end(), axis_x->max(), [](auto &p, double x) { return p.x() < x; });
 
-    int num_points = std::max<int>(end - begin, 1);
-    int pixels_per_point = width() / num_points;
+      int num_points = std::max<int>(end - begin, 1);
+      int pixels_per_point = width() / num_points;
 
-    s.series->setPointsVisible(pixels_per_point > 20);
+      s.series->setPointsVisible(pixels_per_point > 20);
+
+      // TODO: On MacOS QChartWidget doesn't work with the OpenGL settings that CameraWidget needs.
+#ifndef __APPLE
+      // OpenGL mode lacks certain features (such as showing points), only use when drawing many points
+      bool use_opengl = pixels_per_point < 1;
+      s.series->setUseOpenGL(use_opengl);
+
+      // Qt doesn't properly apply device pixel ratio in OpenGL mode
+      QApplication* application = static_cast<QApplication *>(QApplication::instance());
+      float scale = use_opengl ? application->devicePixelRatio() : 1.0;
+
+      QPen pen = s.series->pen();
+      pen.setWidth(2.0 * scale);
+      s.series->setPen(pen);
+#endif
+    }
   }
 
   scene()->invalidate({}, QGraphicsScene::ForegroundLayer);