JKQtPlotter/examples/geo_arrows/README.md

Example (JKQTPlotter): Plotting Arrows

This project shows the capabilities of JKQTPlotter to also draw arrows as geometric elements, using JKQTPGeoArrow. The arrow head/tail are defined by the enum values in JKQTPLineDecoratorStyle.

The source code of the main application can be found in geo_arrows.cpp. First a plot is generated. Then several types of arrows are plotted onto the JKQtPlotter.

Different types of arrows

A first table shows all available arrow tips in different sizes.

     for (size_t i=0; i<static_cast<size_t>(JKQTPLineDecoratorCount); i++) {
        auto const decor=static_cast<JKQTPLineDecoratorStyle>(i);
        plot.addGraph(a=new JKQTPGeoArrow(&plot, 0.1,  arr_y, 0.3, arr_y+0.05, QColor("red"), decor, JKQTPNoDecorator, 0.2));
        plot.addGraph(a=new JKQTPGeoArrow(&plot, 0.4,  arr_y, 0.6, arr_y+0.05, QColor("red"), decor, JKQTPNoDecorator, 0.5));
        plot.addGraph(a=new JKQTPGeoArrow(&plot, 0.7,  arr_y, 0.9, arr_y+0.05, QColor("red"), decor, JKQTPNoDecorator, 1));
        plot.addGraph(a=new JKQTPGeoArrow(&plot, 1.0,  arr_y, 1.3, arr_y+0.05, QColor("red"), decor, JKQTPNoDecorator, 2));
        plot.addGraph(a=new JKQTPGeoArrow(&plot, 1.4,  arr_y, 1.7, arr_y+0.05, QColor("red"), decor, JKQTPNoDecorator, 3));
        plot.addGraph(new JKQTPGeoText(&plot, a->getX2()+0.05, a->getY2(), "\\verb{"+JKQTPLineDecoratorStyle2String(decor)+"}", 12, a->getLineColor()));
        arr_y+=arr_deltay;
    }

Here is the resulting table:

Note how the head-size scales with the line-width, but not linearly, but rather sub-linearly, so the tips do not grow too strongly.

Also note that all arrows end at the designated line-end (here indicated by dashed grey lines), even circles and rectangle:

Classes with support for arrows

You can use JKQTPGeoArrow and JKQTPGeoLine to draw arrows (JKQTPGeoArrow is just a convenience class that enables arrows by default, otherwise it is equal to JKQTPGeoLine).

In addition, also other classes can show line-decorators:

• JKQTPGeoLine
• JKQTPGeoPolyLines
• JKQTPGeoInfiniteLine .

Here is an example of how to actiavate them for a JKQTPGeoPolyLines:

    QVector<QPointF> points; points<<QPointF(3,  0.6)<<QPointF(4,  0.5)<<QPointF(3,  1.2)<<QPointF(4,  1.0);
    JKQTPGeoPolyLines* polyLine=new JKQTPGeoPolyLines(&plot, points, QColor("blue"));
    polyLine->setHeadDecoratorStyle(JKQTPFilledDoubleArrow);
    polyLine->setTailDecoratorStyle(JKQTPCircleDecorator);
    plot.addGraph(polyLine);

Here is the result:

For the class JKQTPGeoInfiniteLine the start can be decorated with an arrow (only if two_sided==false!):

    JKQTPGeoInfiniteLine* infLine=new JKQTPGeoInfiniteLine(&plot, 1.5, 0.2, 1, 0.25, QColor("blue"), 2);
    infLine->setHeadDecoratorStyle(JKQTPFilledDoubleArrow);
    plot.addGraph(infLine);

Here is the result:

Screenshot

The result of the complete example looks like this: