JKQtPlotter/examples/simpletest_filledgraphs/README.md

Example (JKQTPlotter): Filled Curve Plots

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

The source code of the main application can be found in jkqtplotter_simpletest_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: