plotter: limit plot update rate

Helps performance, and faster looks worse on the screen.

Signed-off-by: Jeff Long <[email protected]>

src/applications/gqrx/mainwindow.cpp

@@ -1796,8 +1796,8 @@ void MainWindow::setIqFftRate(int fps)
             ui->plotter->setRunningState(true);
     }
 
-    // Limit to 250 fps
-    if (interval > 3 && iq_fft_timer->isActive())
+    // Limit to 500 fps
+    if (interval > 1 && iq_fft_timer->isActive())
         iq_fft_timer->setInterval(interval);
 
     uiDockFft->setWfResolution(ui->plotter->getWfTimeRes());

src/qtgui/dockfft.ui

@@ -646,6 +646,11 @@
               <property name="currentIndex">
                <number>0</number>
               </property>
+              <item>
+               <property name="text">
+                <string>500 fps</string>
+               </property>
+              </item>
               <item>
                <property name="text">
                 <string>250 fps</string>

src/qtgui/plotter.cpp

@@ -164,6 +164,7 @@ CPlotter::CPlotter(QWidget *parent) : QFrame(parent)
 
     // always update waterfall
     tlast_wf_ms = 0;
+    tlast_plot_drawn_ms = 0;
     tlast_wf_drawn_ms = 0;
     wf_valid_since_ms = 0;
     msec_per_wfline = 0;
@@ -1246,7 +1247,8 @@ void CPlotter::draw(bool newData)
     const double frameTime = 1.0 / (double)fft_rate;
 
     // Redraw the plot if it is visible.
-    const bool doPlotter = !m_2DPixmap.isNull();
+    const bool doPlotter = (!m_2DPixmap.isNull()
+        && tnow_ms >= tlast_plot_drawn_ms + PLOTTER_UPDATE_LIMIT_MS);
 
     // Do not waste time with histogram calculations unless in this mode.
     const bool doHistogram = m_PlotMode == PLOT_MODE_HISTOGRAM;
@@ -1523,6 +1525,8 @@ void CPlotter::draw(bool newData)
     // get/draw the 2D spectrum
     if (doPlotter)
     {
+        tlast_plot_drawn_ms = tnow_ms;
+
         m_2DPixmap.fill(PLOTTER_BGD_COLOR);
         QPainter painter2(&m_2DPixmap);
 

src/qtgui/plotter.h

@@ -18,6 +18,7 @@
 #define PEAK_CLICK_MAX_V_DISTANCE 20 //Maximum vertical distance of clicked point from peak
 #define PEAK_WINDOW_HALF_WIDTH    10
 #define PEAK_UPDATE_PERIOD       100 // msec
+#define PLOTTER_UPDATE_LIMIT_MS   32 // 32ms = 31.25 Hz
 
 #define MARKER_OFF std::numeric_limits<qint64>::min()
 
@@ -330,6 +331,7 @@ public slots:
 
     // Waterfall averaging
     quint64     tlast_wf_ms;        // last time waterfall has been updated
+    quint64     tlast_plot_drawn_ms;// last time the plot was drawn
     quint64     tlast_wf_drawn_ms;  // last time waterfall was drawn
     quint64     wf_valid_since_ms;  // last time before action that invalidates time line
     double      msec_per_wfline{};  // milliseconds between waterfall updates