ui/drawLaneLines: read the accel from the submaster outside of the loop (#28145)

* read the accel from the submaster outside of the loop.

* const max_idx

* remove data copy and converting from list to vector

* correct name is len

* fix drawing last point

* add comment, remove right_points

* fix

---------

Co-authored-by: Shane Smiskol <shane@smiskol.com>

selfdrive/ui/qt/onroad.cc

@@ -513,17 +513,17 @@ void AnnotatedCameraWidget::drawLaneLines(QPainter &painter, const UIState *s) {
   // paint path
   QLinearGradient bg(0, height(), 0, 0);
   if (sm["controlsState"].getControlsState().getExperimentalMode()) {
-    const QVector<QPointF> right_points = scene.track_vertices.mid(0, scene.track_vertices.length() / 2);
-
-    for (int i = 0; i < right_points.length(); i++) {
-      const auto &acceleration = sm["uiPlan"].getUiPlan().getAccel();
-      if (i >= acceleration.size()) break;
+    // The first half of track_vertices are the points for the right side of the path
+    // and the indices match the positions of accel from uiPlan
+    const auto &acceleration = sm["uiPlan"].getUiPlan().getAccel();
+    const int max_len = std::min<int>(scene.track_vertices.length() / 2, acceleration.size());
 
+    for (int i = 0; i < max_len; ++i) {
       // Some points are out of frame
-      if (right_points[i].y() < 0 || right_points[i].y() > height()) continue;
+      if (scene.track_vertices[i].y() < 0 || scene.track_vertices[i].y() > height()) continue;
 
       // Flip so 0 is bottom of frame
-      float lin_grad_point = (height() - right_points[i].y()) / height();
+      float lin_grad_point = (height() - scene.track_vertices[i].y()) / height();
 
       // speed up: 120, slow down: 0
       float path_hue = fmax(fmin(60 + acceleration[i] * 35, 120), 0);
@@ -536,7 +536,7 @@ void AnnotatedCameraWidget::drawLaneLines(QPainter &painter, const UIState *s) {
       bg.setColorAt(lin_grad_point, QColor::fromHslF(path_hue / 360., saturation, lightness, alpha));
 
       // Skip a point, unless next is last
-      i += (i + 2) < right_points.length() ? 1 : 0;
+      i += (i + 2) < max_len ? 1 : 0;
     }
 
   } else {