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.

example plot

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";

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:

This uses the PlotStyle's cmap to generate 256 RGB(A) colour-map values, then outputs an indexed PNG.