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Fix adaptive sampling performance on scatterplots 

QCustomPlot's adaptive sampling decimates the data to be plotted based
on the screen resolution.  Specifically, if many data points fit within
the same pixel on the X (key) axis, then QCustomPlot attempts to plot
only the min value, the max value, and a few values in-between to
maintain a good "density" on the Y (value) axis.

The density QCustomPlot wants is about one datapoint for every 4 pixels
covered by the value range of a single X (key) pixel.  Unfortunately,
this calculation is flawed if all values also fit within a single pixel
on the Y (value) axis - so this change fixes that bug.
This commit is contained in:
Kevin Hogan 2021-04-14 18:48:50 -04:00 committed by Wireshark GitLab Utility
parent 293eb2f534
commit 92e652ebfa
1 changed files with 7 additions and 3 deletions
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10
ui/qt/widgets/qcustomplot.cpp
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@ -21821,8 +21821,10 @@ void QCPGraph::getOptimizedScatterData(QVector<QCPGraphData> *scatterData, QCPGr
if (intervalDataCount >= 2) // last pixel had multiple data points, consolidate them
{
// determine value pixel span and add as many points in interval to maintain certain vertical data density (this is specific to scatter plot):
double valuePixelSpan = qAbs(valueAxis->coordToPixel(minValue)-valueAxis->coordToPixel(maxValue));
int dataModulo = qMax(1, qRound(intervalDataCount/(valuePixelSpan/4.0))); // approximately every 4 value pixels one data point on average
// [ However, make sure that the span is at least 1 pixel ]
double valuePixelSpan = qMax(1.0, qAbs(valueAxis->coordToPixel(minValue)-valueAxis->coordToPixel(maxValue)));
double pointsToAdd = valuePixelSpan/4.0; // add approximately one data point for every 4 value pixels
int dataModulo = qMax(1, qRound(intervalDataCount/pointsToAdd));
QCPGraphDataContainer::const_iterator intervalIt = currentIntervalStart;
int c = 0;
while (intervalIt != it)
@ -21864,8 +21866,10 @@ void QCPGraph::getOptimizedScatterData(QVector<QCPGraphData> *scatterData, QCPGr
if (intervalDataCount >= 2) // last pixel had multiple data points, consolidate them
{
// determine value pixel span and add as many points in interval to maintain certain vertical data density (this is specific to scatter plot):
// [ However, make sure that the span is at least 1 pixel ]
double valuePixelSpan = qAbs(valueAxis->coordToPixel(minValue)-valueAxis->coordToPixel(maxValue));
int dataModulo = qMax(1, qRound(intervalDataCount/(valuePixelSpan/4.0))); // approximately every 4 value pixels one data point on average
double pointsToAdd = valuePixelSpan/4.0; // add approximately one data point for every 4 value pixels
int dataModulo = qMax(1, qRound(intervalDataCount/pointsToAdd));
QCPGraphDataContainer::const_iterator intervalIt = currentIntervalStart;
int intervalItIndex = int(intervalIt-mDataContainer->constBegin());
int c = 0;