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77 lines
3.0 KiB
Markdown
77 lines
3.0 KiB
Markdown
# Example (JKQTPlotter): Filled Curve Plots {#JKQTPlotterFilledGraphs}
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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.
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The source code of the main application can be found in [`filledgraphs.cpp`](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/filledgraphs/filledgraphs.cpp).
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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).
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```.cpp
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size_t columnX=ds->addLinearColumn(256, 0, 255, "x");
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```
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And three columns with 256 entries each, which will be filled with the R-, G- and B-histograms of an image `example.bmp`:
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```.cpp
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size_t columnR=ds->addColumn(256, "historam_R");
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size_t columnG=ds->addColumn(256, "historam_G");
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size_t columnB=ds->addColumn(256, "historam_B");
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```
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In order to calculate the histograms, first all enries in the columns are set to 0:
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```.cpp
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ds->setAll(columnG, 0);
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ds->setAll(columnR, 0);
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ds->setAll(columnB, 0);
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```
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Finally the histogram is calculated:
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```.cpp
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QImage image(":/example.bmp");
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for (int y=0; y<image.height(); y++) {
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for (int x=0; x<image.width(); x++) {
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QRgb pix=image.pixel(x,y);
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ds->inc(columnR, qRed(pix), 1);
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ds->inc(columnG, qGreen(pix), 1);
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ds->inc(columnB, qBlue(pix), 1);
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}
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}
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ds->scaleColumnValues(columnR, 100.0/static_cast<double>(image.width()*image.height()));
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ds->scaleColumnValues(columnG, 100.0/static_cast<double>(image.width()*image.height()));
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ds->scaleColumnValues(columnB, 100.0/static_cast<double>(image.width()*image.height()));
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```
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Finally three `JKQTPFilledCurveXGraph` objects are generated and added to the plot (here we show the code for the R-channel only):
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```.cpp
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JKQTPFilledCurveXGraph* graphR=new JKQTPFilledCurveXGraph(&plot);
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// set graph titles
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graphR->setTitle("R-channel");
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// set graph colors (lines: non-transparent, fill: semi-transparent
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QColor col;
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col=QColor("red"); graphR->setColor(col);
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col.setAlphaF(0.25); graphR->setFillColor(col);
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// set data
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graphR->setXColumn(columnX); graphR->setYColumn(columnR);
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// add the graphs to the plot, so they are actually displayed
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plot.addGraph(graphR);
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```
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The curves are fille with a semi-transparent color, which is achieved by setting `col.setAlphaF(0.25)` on the graph color `col`.
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The result looks like this:
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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:
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