Catplotlib (C++ mini-plotting)

Catplotlib is a lightweight, header-first C++ plotting library that renders to SVG. It provides a tiny, familiar API reminiscent of matplotlib for quick plots directly from C++ without external runtime dependencies.

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Features (v0.1)

• Line plots and scatter plots
• Automatic axis limits and nice ticks
• Title, x-label, y-label
• Pure C++17, outputs an SVG file
• Grid and legend toggles (basic)
• Multiple subplots (subplot(nrows, ncols, index))

Planned Features

• PNG export
• Dear ImGui/SDL interactive backend
• Improved text rendering with font metrics
• Enhanced multi-axes layouts
• Advanced legend and grid customization
• More plot types (bar, histogram, etc.)
• Better error handling and validation
• Documentation improvements
• Performance optimizations
• Additional examples and tutorials

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Build

Requirements:

• CMake 3.15+
• A C++17 compiler (MSVC, clang, or gcc)

Steps:

cmake -S . -B build
cmake --build build --config Release

This builds the catplotlib library and the example catplot_example.

Run the example

# After building as above
cd build
./catplot_example   # on Windows: .\\Release\\catplot_example.exe (multi-config generators)

It produces catplot_example.svg in the working directory.

Basic usage

#include "catplot/catplot.hpp"
#include <vector>

int main() {
    using namespace catplot;
    Figure fig(800, 600);
    auto& ax = fig.axes();

    std::vector<double> x{0, 1, 2, 3};
    std::vector<double> y{0, 1, 0, 1};

    ax.plot(x, y, Rgba::Blue(), 2.0);
    ax.scatter(x, y, 4.0, Rgba::Red());
    ax.set_title("Hello catplot");
    ax.set_xlabel("x");
    ax.set_ylabel("y");
    ax.grid(true);
    ax.legend(true); // requires series with labels

    fig.save("out.svg");
}

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API overview

• Figure(int widthPx = 800, int heightPx = 600)
• Axes& Figure::axes()
• Axes& Figure::subplot(int nrows, int ncols, int index1based)
• void Axes::plot(const std::vector<double>& x, const std::vector<double>& y, const Rgba& color, double lineWidthPx)
• void Axes::plot(..., const std::string& label) (optional)
• void Axes::scatter(const std::vector<double>& x, const std::vector<double>& y, double radiusPx, const Rgba& color)
• void Axes::scatter(..., const std::string& label) (optional)
• void Axes::set_title(const std::string&), set_xlabel, set_ylabel
• void Axes::grid(bool), void Axes::legend(bool)
• void Figure::save(const std::string& path) -> SVG
• void Figure::save_png(const std::string& path) -> Not yet implemented (stub)

Example Gallery

Here are some example plots generated with catplot:

Note

• NumBits I use in this is my own lightweight number computation library like mini numpy but in cpp.
• SVG text rendering uses browser defaults (sans-serif). There is no font metrics; label placement is approximate but readable.
• For multi-axes layouts, legends, grid, and styles, contributions are welcome.
• PNG export and Dear ImGui/SDL interactive backend are on the roadmap. The save_png API exists as a stub and currently throws.

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License

MIT