parallelbrot

Mandelbrot set renderer with CPU, OpenCL and CUDA backends — a Python package for generating fractal images, and an interactive real-time viewer.

Mandelbrot Renderer Demo

Install

pip install parallelbrot
# or
uv add parallelbrot

Wheels are abi3, so one wheel per platform covers CPython 3.9 and up.

Python API

import parallelbrot as pb

image = pb.render(1920, 1080)                 # (1080, 1920, 4) float32 RGBA

Zoom in on the seahorse valley, and save it:

from PIL import Image

image = pb.render(
    1920, 1080,
    center=(-0.743644, 0.131826),
    zoom=4000,
    max_iterations=1000,
    color_scheme="fire",
)
Image.fromarray((image * 255).astype("uint8")).save("seahorse.png")

`render()`

Argument	Default	Meaning
`width`, `height`	—	Output size in pixels
`center`	`(-0.5, 0.0)`	Point on the complex plane at the image centre
`zoom`	`1.0`	Magnification; the view spans `4 / zoom`
`max_iterations`	`128`	Escape limit — raise it as you zoom in
`color_scheme`	`"fire"`	`ultra_fractal`, `fire`, `ocean` or `psychedelic`
`backend`	`"auto"`	`auto`, `cpu`, `opencl` or `cuda`
`origin`	`"upper"`	`upper` puts row 0 at the top, as images expect

Returns an (height, width, 4) float32 array with values in [0, 1].

Choosing a backend

pb.available_backends()   # ('cpu',) — compiled in and a device is present
pb.compiled_backends()    # ('cpu', 'opencl') — compiled in, device or not
pb.device_name("opencl")  # 'NVIDIA GeForce RTX 4070' or None
pb.has_openmp()           # is the CPU backend multi-threaded?

backend="auto" picks the fastest backend that has a working device, falling back to the CPU.

Rendering releases the GIL, so calls from separate threads run in parallel:

from concurrent.futures import ThreadPoolExecutor

with ThreadPoolExecutor() as pool:                       # renders a zoom
    frames = list(pool.map(                              # sequence in parallel
        lambda z: pb.render(640, 480, zoom=z), [2**i for i in range(12)]
    ))

Which backends do you get?

	CPU (OpenMP)	OpenCL	CUDA
`pip install` / `uv add`	✅	—	—
conda-forge	✅	✅	✅
built from source	✅	if headers found	if `nvcc` found

PyPI wheels are CPU-only on purpose. Linking OpenCL makes the extension require an ICD loader at import time, which would break the package on machines without a GPU driver — including for people who only wanted the CPU backend. conda can declare that loader as a dependency, so the GPU builds live there.

The CPU backend is not a toy: OpenMP parallelises across rows with dynamic scheduling, since interior points cost far more than exterior ones. A 1920×1080 frame at 1000 iterations takes 37 ms on 16 cores, against 506 ms single-threaded.

Interactive viewer

A real-time pan-and-zoom window, built separately from the Python package.

make install-deps-ubuntu     # or -fedora, -arch, -macos
make opencl && bin/mandelbrot_opencl   # any GPU — recommended
make cuda   && bin/mandelbrot_cuda     # NVIDIA only, fastest
make cpu    && bin/mandelbrot_cpu      # always works

Input	Action
Mouse drag	Pan
Mouse wheel	Zoom, centred on the cursor
Arrow keys	Pan
`+` / `-`	Increase / decrease iterations
`C`	Cycle colour schemes
`R`	Reset view
`Esc`	Quit

make help lists every target; make check-opencl and make check-cuda report what your machine can do.

Viewer dependencies

Component	Linux	macOS	Windows (MSYS2)
Compiler	`g++` (GCC ≥ 9)	Apple Clang	MinGW-w64 g++
Build	`make`, `pkg-config`	`make`, `pkg-config`	GNU make, `pkg-config`
OpenGL	`libgl1-mesa-dev`, `libglew-dev`	built-in	`mingw-w64-x86_64-glew`
GLFW 3	`libglfw3-dev`	`brew install glfw`	`mingw-w64-x86_64-glfw`
OpenCL	`ocl-icd-opencl-dev` + driver	built-in framework	`mingw-w64-x86_64-opencl-icd`
CUDA (optional)	`nvidia-cuda-toolkit` + driver 470+	not supported	CUDA Toolkit

GPU drivers: NVIDIA needs the proprietary driver or nvidia-opencl-dev; AMD needs rocm-opencl-runtime or mesa-opencl-icd; Intel needs intel-opencl-icd. macOS provides OpenCL itself.

Building from source

git clone https://github.com/prathamhole/parallelbrot
cd parallelbrot

uv sync                      # venv + dev dependencies, package built editable
uv run pytest                # 16 tests
uv run python -c "import parallelbrot as p; print(p.compiled_backends())"

Without uv:

pip install -e .             # rebuilds the C++ on import when sources change
pytest

Build options are Meson features, so absent tooling degrades the build rather than failing it:

uv sync -C setup-args=-Dopencl=enabled    # fail if OpenCL is missing
uv sync -C setup-args=-Dopenmp=disabled   # single-threaded CPU backend
python -m build --wheel                   # a cp3XX-abi3 wheel

macOS needs brew install libomp for a multi-threaded CPU backend — Apple Clang ships without OpenMP. pb.has_openmp() tells you which you got.

Layout

include/parallelbrot/core.hpp   Shared View struct + backend entry points
src/core/                       Compute cores — no windowing, no Python
src/cpu|opencl|cuda/            Interactive frontends + device kernels
src/python/                     CPython extension (limited API)
src/parallelbrot/               Python package
meson.build, pyproject.toml     Wheel build
Makefile                        Interactive viewer binaries

The compute cores carry no GLFW, OpenGL or Python headers, so the same code serves the viewer, the Python package and the tests.

See docs/RELEASING.md for the release process.

License

MIT — see LICENSE.

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0.2.1

Sep 8, 2026 6 files

0.1.1

Sep 7, 2026 6 files

This release

0.1.0 This release

Sep 7, 2026 6 files

parallelbrot 0.1.0

parallelbrot

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render()

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`render()`