cabana: optimize sparkline rendering by reducing points in horizontal segments (#35689)

Optimize sparkline rendering by reducing redundant points in flat segments

tools/cabana/chart/sparkline.cc

@@ -4,51 +4,97 @@
 #include <limits>
 #include <QPainter>
 
-void Sparkline::update(const MessageId &msg_id, const cabana::Signal *sig, double last_msg_ts, int range, QSize size) {
-  points.clear();
-  double value = 0;
-  auto [first, last] = can->eventsInRange(msg_id, std::make_pair(last_msg_ts -range, last_msg_ts));
-  for (auto it = first; it != last; ++it) {
-    if (sig->getValue((*it)->dat, (*it)->size, &value)) {
-      points.emplace_back(((*it)->mono_time - (*first)->mono_time) / 1e9, value);
-    }
-  }
-
-  if (points.empty() || size.isEmpty()) {
+void Sparkline::update(const cabana::Signal *sig, CanEventIter first, CanEventIter last, int range, QSize size) {
+  if (first == last || size.isEmpty()) {
     pixmap = QPixmap();
     return;
   }
 
-  const auto [min, max] = std::minmax_element(points.begin(), points.end(),
-                                              [](auto &l, auto &r) { return l.y() < r.y(); });
-  min_val = min->y() == max->y() ? min->y() - 1 : min->y();
-  max_val = min->y() == max->y() ? max->y() + 1 : max->y();
-  freq_ = points.size() / std::max(points.back().x() - points.front().x(), 1.0);
+  points_.clear();
+  min_val = std::numeric_limits<double>::max();
+  max_val = std::numeric_limits<double>::lowest();
+  points_.reserve(std::distance(first, last));
+
+  uint64_t start_time = (*first)->mono_time;
+  double value = 0.0;
+  for (auto it = first; it != last; ++it) {
+    if (sig->getValue((*it)->dat, (*it)->size, &value)) {
+      min_val = std::min(min_val, value);
+      max_val = std::max(max_val, value);
+      points_.emplace_back(((*it)->mono_time - start_time) / 1e9, value);
+    }
+  }
+
+  if (points_.empty()) {
+    pixmap = QPixmap();
+    return;
+  }
+
+  freq_ = points_.size() / std::max(points_.back().x() - points_.front().x(), 1.0);
   render(sig->color, range, size);
 }
 
 void Sparkline::render(const QColor &color, int range, QSize size) {
-  const double xscale = (size.width() - 1) / (double)range;
-  const double yscale = (size.height() - 3) / (max_val - min_val);
-  for (auto &v : points) {
-    v = QPoint(v.x() * xscale, 1 + std::abs(v.y() - max_val) * yscale);
+  // Adjust for flat lines
+  bool is_flat_line = min_val == max_val;
+  if (is_flat_line) {
+    min_val -= 1.0;
+    max_val += 1.0;
   }
 
+  // Calculate scaling
+  const double xscale = (size.width() - 1) / (double)range;
+  const double yscale = (size.height() - 3) / (max_val - min_val);
+  bool draw_individual_points = (points_.back().x() * xscale / points_.size()) > 8.0;
+
+  // Transform or downsample points
+  render_points_.reserve(points_.size());
+  render_points_.clear();
+  if (draw_individual_points) {
+    for (const auto &p : points_) {
+      render_points_.emplace_back(p.x() * xscale, 1.0 + (max_val - p.y()) * yscale);
+    }
+  } else if (is_flat_line) {
+    double y = size.height() / 2.0;
+    render_points_.emplace_back(0.0, y);
+    render_points_.emplace_back(points_.back().x() * xscale, y);
+  } else {
+    double prev_y = points_.front().y();
+    render_points_.emplace_back(points_.front().x() * xscale, 1.0 + (max_val - prev_y) * yscale);
+    bool in_flat = false;
+
+    for (size_t i = 1; i < points_.size(); ++i) {
+      const auto &p = points_[i];
+      double y = p.y();
+      if (std::abs(y - prev_y) < 1e-6) {
+        in_flat = true;
+      } else {
+        if (in_flat) render_points_.emplace_back(points_[i - 1].x() * xscale, 1.0 + (max_val - prev_y) * yscale);
+        render_points_.emplace_back(p.x() * xscale, 1.0 + (max_val - y) * yscale);
+        in_flat = false;
+      }
+      prev_y = y;
+    }
+    if (in_flat) render_points_.emplace_back(points_.back().x() * xscale, 1.0 + (max_val - prev_y) * yscale);
+  }
+
+  // Render to pixmap
   qreal dpr = qApp->devicePixelRatio();
-  size *= dpr;
-  if (size != pixmap.size()) {
-    pixmap = QPixmap(size);
+  const QSize pixmap_size = size * dpr;
+  if (pixmap.size() != pixmap_size) {
+    pixmap = QPixmap(pixmap_size);
   }
   pixmap.setDevicePixelRatio(dpr);
   pixmap.fill(Qt::transparent);
   QPainter painter(&pixmap);
-  painter.setRenderHint(QPainter::Antialiasing, points.size() < 500);
+  painter.setRenderHint(QPainter::Antialiasing, render_points_.size() <= 500);
   painter.setPen(color);
-  painter.drawPolyline(points.data(), points.size());
+  painter.drawPolyline(render_points_.data(), render_points_.size());
+
   painter.setPen(QPen(color, 3));
-  if ((points.back().x() - points.front().x()) / points.size() > 8) {
-    painter.drawPoints(points.data(), points.size());
+  if (draw_individual_points) {
+    painter.drawPoints(render_points_.data(), render_points_.size());
   } else {
-    painter.drawPoint(points.back());
+    painter.drawPoint(render_points_.back());
   }
 }

tools/cabana/chart/sparkline.h

@@ -9,7 +9,7 @@
 
 class Sparkline {
 public:
-  void update(const MessageId &msg_id, const cabana::Signal *sig, double last_msg_ts, int range, QSize size);
+  void update(const cabana::Signal *sig, CanEventIter first, CanEventIter last, int range, QSize size);
   inline double freq() const { return freq_; }
   bool isEmpty() const { return pixmap.isNull(); }
 
@@ -20,6 +20,7 @@ public:
 private:
   void render(const QColor &color, int range, QSize size);
 
-  std::vector<QPointF> points;
+  std::vector<QPointF> points_;
+  std::vector<QPointF> render_points_;
   double freq_ = 0;
 };

tools/cabana/signalview.cc

@@ -634,11 +634,12 @@ void SignalView::updateState(const std::set<MessageId> *msgs) {
     QSize size(available_width - value_width,
                delegate->button_size.height() - style()->pixelMetric(QStyle::PM_FocusFrameVMargin) * 2);
 
+    auto [first, last] = can->eventsInRange(model->msg_id, std::make_pair(last_msg.ts -settings.sparkline_range, last_msg.ts));
     QFutureSynchronizer<void> synchronizer;
     for (int i = first_visible.row(); i <= last_visible.row(); ++i) {
       auto item = model->getItem(model->index(i, 1));
       synchronizer.addFuture(QtConcurrent::run(
-          &item->sparkline, &Sparkline::update, model->msg_id, item->sig, last_msg.ts, settings.sparkline_range, size));
+          &item->sparkline, &Sparkline::update, item->sig, first, last, settings.sparkline_range, size));
     }
     synchronizer.waitForFinished();
   }