Example (JKQTPlotter): Filled Curve Plots

This project (see ./examples/filledgraphs/) simply creates a JKQTPlotter widget (as a new window) and adds several filled curve graphs (Histograms). Data is initialized from QVector<int> objects.

The source code of the main application can be found in filledgraphs.cpp.

First the data columns for three x-y-curves are generated. One column of x-values with entries 0,1,2,...,254,255 (256 entries).

size_t columnX=ds->addLinearColumn(256, 0, 255, "x");

And three columns with 256 entries each, which will be filled with the R-, G- and B-histograms of an image example.bmp:

size_t columnR=ds->addColumn(256, "historam_R");
size_t columnG=ds->addColumn(256, "historam_G");
size_t columnB=ds->addColumn(256, "historam_B");

In order to calculate the histograms, first all enries in the columns are set to 0:

ds->setAll(columnG, 0);
ds->setAll(columnR, 0);
ds->setAll(columnB, 0);

Finally the histogram is calculated:

QImage image(":/example.bmp");
for (int y=0; y<image.height(); y++) {
    for (int x=0; x<image.width(); x++) {
        QRgb pix=image.pixel(x,y);
        ds->inc(columnR, qRed(pix), 1);
        ds->inc(columnG, qGreen(pix), 1);
        ds->inc(columnB, qBlue(pix), 1);
    }
}
ds->scaleColumnValues(columnR, 100.0/static_cast<double>(image.width()*image.height()));
ds->scaleColumnValues(columnG, 100.0/static_cast<double>(image.width()*image.height()));
ds->scaleColumnValues(columnB, 100.0/static_cast<double>(image.width()*image.height()));

Finally three JKQTPFilledCurveXGraph objects are generated and added to the plot (here we show the code for the R-channel only):

JKQTPFilledCurveXGraph* graphR=new JKQTPFilledCurveXGraph(&plot);
 
// set graph titles
graphR->setTitle("R-channel");
 
// set graph colors (lines: non-transparent, fill: semi-transparent
QColor col;
col=QColor("red"); graphR->setColor(col);
col.setAlphaF(0.25); graphR->setFillColor(col);
 
// set data
graphR->setXColumn(columnX); graphR->setYColumn(columnR);
 
 
// add the graphs to the plot, so they are actually displayed
plot.addGraph(graphR);

The curves are fille with a semi-transparent color, which is achieved by setting col.setAlphaF(0.25) on the graph color col.

The result looks like this:

If you use JKQTPFilledCurveYGraph instead of JKQTPFilledCurveXGraph, the curve will not be filled until the y=0-axis, but until the x=0-axis. Of course you will also have to swap the x- and y-data columns. The result will look like this: