Basic C++ plots

This is a minimal header-only and dependency-free C++ plotting library.

It's maintained mostly for internal Signalsmith Audio use, so I'm adding features as I need them.

Design choices

• SVG output only
• auto-styled lines and fills
  • simultaneous colour/dash/hatch/marker sequences for accessibility
  • styling done via (customisable) CSS where possible
  • custom JS (included as source or URL)
• explicit labelling on lines, or legends
• values labelled with three levels: major/minor/tick
  • no explicit axis-lines, use major gridlines instead
• simplifies paths
  • attempts not to draw out-of-view data
  • drops points along almost-straight lines
• each plot's edge can have multiple partial axes
• basic grid (each row/column stretches to contain its contents)
• animated graphs with <animate> (SMIL)

Limitations

• only 2D plots supported
• no automatic label placement or de-collision
• text lengths are heuristically estimated

How to use

All you need is the header file:

#include "plot.h";

View the API docs for complete info.

Basic example: drawing lines

Here's a minimal example, which sets up a 2D plot, adds some grid-lines/ticks:

// Set up a plot
signalsmith::plot::Plot2D plot;

// Place the grid/ticks
plot.x.majors(0, 10).tick(5).minor(3.5);
ploy.y.major(0);

// If you don't set the scale, it will guess from data/ticks
plot.x.linear(0, 15);
// You can use custom scales, using any function
// (or lambda) which accepts/returns `double`
plot.y.range(std::log, 1, 1000);

// Set up a line
auto &line = plot.line();
for (auto &p : points) {
	// Add points as x/y pairs
	line.add(p.x, p.y);
}
// or from array (using `.size()` if not specified)
line.addArray(xArr, yArr);

plot.write("example.svg");

More examples

See examples.cpp for code examples. Here are the images generated by that code:

API principles

You create a top-level object, which could be a Figure or a Plot2D:

signalsmith::plot::Plot2D plot;

When you create a sub-object (line, sub-plot, etc.), you are returned a reference. These elements are deliberately not copyable, so if you use auto instead of auto & it will complain.

auto &line = plot.line();

Many methods return a reference to the object, allowing you to chain them together, e.g.:

plot.x.major(0, 10).minor(5);

Heat maps

There's an additional module in heatmap.h for pixel-based heat-maps:

The colour map can be overridden by #defineing SIGNALSMITH_HEATMAP_RGB (before including heatmap.h), which should be the name of a function which accepts (double v, uint8_t *rgb) for v in 0-1.

Development

Testing

There aren't any unit tests, just a visual check of the example plots.

License

Released as 0BSD. If you need anything else, get in touch. 🙂