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43 lines
2.1 KiB
Markdown
43 lines
2.1 KiB
Markdown
# Example (JKQTPlotter): Plotting Parametric Mathematical Curves as Line Graphs {#JKQTPlotterEvalCurves}
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## Basics
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This project (see `./examples/evalcurve/`) demonstrates how to plot mathematical functions as line graphs. The functions may be defined as static C functions, C++ functors or c++ inline functions.
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[TOC]
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# Simple C++ inline function
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The example shows how to plot a simple C++ inline function:
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```.cpp
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JKQTPXYFunctionLineGraph* func1=new JKQTPXYFunctionLineGraph(plot);
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func1->setPlotFunctionFunctor([](double t) -> QPointF {
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const double a=5;
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const double b=4;
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const double delta=JKQTPSTATISTICS_PI/4.0;
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return QPointF(sin(a*t+delta), sin(b*t));
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});
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func1->setTRange(0, 2.0*JKQTPSTATISTICS_PI);
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func1->setTitle("C++-inline function $[ sin(5{\\cdot}t+\\pi/4), sin(4{\\cdot}t) ]$");
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plot->addGraph(func1);
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```
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Note that here a functor is defined, which calculates the points on a [Lissajous Curve](https://en.wikipedia.org/wiki/Lissajous_curve), i.e. a function mapping a parameter `t` to a two-dimensional point `QPointF` with `x=sin(a*t+delta)`and `y=sin(b*t)`. This function is evaluated on a range of values for `t`, set by
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```.cpp
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func1->setTRange(0, 2.0*JKQTPSTATISTICS_PI);
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```
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The class uses an adaptive algorithm, which determines by the local slope, at how many points (or how close points) the functor has to be evaluated.
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# Screenshot
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This code snippets above result in a plot like this:
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# Notes
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Just as shown in [examples/functionplot](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/functionplot) for JKQTPXFunctionLineGraph and JKQTPYFunctionLineGraph, different types of functions can be used to plot. Either simple C++ inline functions, that take a `double t` and return a `QPointF`, or functions that additionally take a parameter vector `void* params`. In that case, the parameters may be provided from different sources, as described in [examples/functionplot](https://github.com/jkriege2/JKQtPlotter/tree/master/examples/functionplot) .
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