Time Series User Chart plotting "Optimisation"

.. default to 5s smoothing for plotting time series (second by
   second samples).

.. if smoothing is applied we sample the smoothed data every
   3 seconds.

.. this reduces the number of points to plot to a 3rd and has
   a significant impact on plot/paint performance.

.. for those users that care about resolution they can set
   the smoothing to none, for those that don't they will
   get faster performance.

src/Charts/UserChart.cpp

@@ -204,9 +204,15 @@ UserChart::setRide(const RideItem *item)
         if (ax != -1 && axisinfo[ax].smooth != 0 && axisinfo[ax].type == GenericAxisInfo::TIME) ysmooth=axisinfo[ax].smooth;
         if (ay != -1 && axisinfo[ay].smooth != 0 && axisinfo[ay].type == GenericAxisInfo::TIME) xsmooth=axisinfo[ay].smooth;
 
-        // lets pre-process the data
-        if (xsmooth >= 2) series.xseries = Utils::smooth_sma(series.xseries, GC_SMOOTH_CENTERED, xsmooth);
-        if (ysmooth >= 2) series.yseries = Utils::smooth_sma(series.yseries, GC_SMOOTH_CENTERED, ysmooth);
+        // lets pre-process the data- and might as well use sampling if losing resolution- some performance benefits here
+        if (xsmooth >= 2) {
+            series.xseries = Utils::smooth_sma(series.xseries, GC_SMOOTH_CENTERED, xsmooth, 3);
+            series.yseries = Utils::sample(series.yseries, 3);
+        }
+        if (ysmooth >= 2) {
+            series.yseries = Utils::smooth_sma(series.yseries, GC_SMOOTH_CENTERED, ysmooth, 3);
+            series.xseries = Utils::sample(series.xseries, 3);
+        }
 
         // DATE groupby (applies to date axis)
         int xgroupby=0, ygroupby=0;
@@ -1736,11 +1742,15 @@ EditUserAxisDialog::EditUserAxisDialog(Context *context, GenericAxisInfo &info)
     setMinimumHeight(250 *dpiXFactor);
 
     // update gui items from Axis info
-    axisname->setText(original.name);
-    log->setChecked(original.log);
     int index=axistype->findData(original.type);
     if (index >=0) axistype->setCurrentIndex(index);
     else axistype->setCurrentIndex(0);
+
+    // show / hide widgets on current config, setting defaults
+    setWidgets();
+
+    axisname->setText(original.name);
+    log->setChecked(original.log);
     fixed->setChecked(original.fixed);
     min->setValue(original.min());
     max->setValue(original.max());
@@ -1754,8 +1764,6 @@ EditUserAxisDialog::EditUserAxisDialog(Context *context, GenericAxisInfo &info)
     connect(okButton, SIGNAL(clicked()), this, SLOT(okClicked()));
     connect(cancelButton, SIGNAL(clicked()), this, SLOT(cancelClicked()));
 
-    // show / hide widgets on current config
-    setWidgets();
 }
 
 void
@@ -1774,6 +1782,7 @@ EditUserAxisDialog::setWidgets()
             break;
 
         case GenericAxisInfo::TIME:
+            smooth->setValue(5); // default to 5 seconds smoothing user can override
             smooth->show();
             smoothlabel->show();
             groupby->setCurrentIndex(0);

src/Core/Utils.cpp

@@ -488,8 +488,11 @@ static double mean(QVector<double>&data, int start, int end)
     return sum/count;
 }
 
+// return vector of smoothed values using mean average of window n samples
+// samples is usually 1 to return every sample, but can be higher in which
+// case sampling is performed before returning results (aka every nth sample)
 QVector<double>
-smooth_sma(QVector<double>&data, int pos, int window)
+smooth_sma(QVector<double>&data, int pos, int window, int samples)
 {
     QVector<double> returning;
 
@@ -516,17 +519,27 @@ smooth_sma(QVector<double>&data, int pos, int window)
 
     while (index < data.count()) {
 
-        returning << mean(data, window_start, window_end);
-
+        if (samples == 1 || index%samples == 0) // sampling
+            returning << mean(data, window_start, window_end);
         index ++;
         window_start++;
         window_end++;
     }
-
     return returning;
 
 }
 
+// nth sampling to match sma above (usually for sampling x where sma has smoothed y
+QVector<double>
+sample(QVector<double>&data, int samples)
+{
+    QVector<double>returning;
+    for (int index=0; index< data.count(); index++)
+        if (samples == 1 || index%samples==0)
+            returning << data.at(index);
+    return returning;
+}
+
 QVector<double>
 smooth_ewma(QVector<double>&data, double alpha)
 {

src/Core/Utils.h

@@ -53,7 +53,8 @@ namespace Utils
     QVector<int> argsort(QVector<QString>&v, bool ascending=false);
     QVector<int> arguniq(QVector<double> &v);
     QVector<int> arguniq(QVector<QString> &v);
-    QVector<double> smooth_sma(QVector<double>&, int pos, int window);
+    QVector<double> smooth_sma(QVector<double>&, int pos, int window, int sample=1);
+    QVector<double> sample(QVector<double>&, int sample); // plain sampling nth sample
     QVector<double> smooth_ewma(QVector<double>&, double alpha);
 
     // used std::sort, std::lower_bound et al