encukou / bresenham

A simple implementation of Bresenham's line drawing algorithm

The bresenham module

A simple implementation of Bresenham's line drawing algorithm.

See the Wikipedia entry for details on what that is.

Note that this is a simple implementation. It is written in Pure Python (without e.g. numpy), so it is relatively slow.

I found some beauty in combining the classic algorithm (whose ingenuity lies in using only integers – a constraint that isn't really as relevant now) with a Python generator (a modern device that follows the spirit of “executable pseudocode”, abstracting away the output subroutine). I hope others can appreciate the code as well.

For serious use, look at these:

• skimage.draw.line, which solves the same problem fast.
• A Numpy-based recipe that generalizes the solution to <var>N</var> dimensions.
• wasabigeom, a 2D vector library made for games

Installation

In a Python virtual environment, do:

python -m pip install bresenham

To install from a Git checkout (in editable mode):

python -m pip install -e.

To install without a virtual envitonment, add the --user option.

Usage

The bresenham(x0, y0, x1, y1) function returns a generator of the coordinates of the line from (x0, y0) to (x1, y1).

For example, the coordinates of a line from (-1, -4) to (3, 2), are:

>>> from bresenham import bresenham

>>> list(bresenham(-1, -4, 3, 2))
[(-1, -4), (0, -3), (0, -2), (1, -1), (2, 0), (2, 1), (3, 2)]

Development

You're welcome to join this project!

If you spot an issue, please report it at the Issues page on Github.

If you'd like to start changing the code or documentation, check out the code locally using:

git clone https://github.com/encukou/bresenham

If you're new to this, please read the this guide about collaborating on Github-hosted projects like this one.

If that doesn't make sense, please e-mail the author for clarification. I'd be happy to help you get started.

bresenham's Issues

Make algorithm work with float input?

Hi! Great work!

Maybe it is possible to make algorithm work with float input by changing line 32 from:
for x in range(dx + 1):
to
for x in range(int(dx + 1)):
in bresenham.py.

This implementation yields false results

Drawing a line from (0,0) to (10,1) should roughly yield these points with Bresenham:

Source

This algorithm however yields the following results:

from bresenham import bresenham
print(list(bresenham(0,0,10,1)))

[(0, 0), (1, 0), (2, 0), (3, 0), (4, 0), (5, 0), (6, 0), (7, 0), (8, 0), (9, 0), (10, 1)]

See also:

• https://www.cs.drexel.edu/~introcs/Fa11/notes/08.3_MoreGraphics/Bresenham.html?CurrentSlide=4
• http://wm.ite.pl/articles/bresenham-demo-line.html

Vectorized implementation

Hi, I put together a vectorized implementation. Are you interested in adding it? If so, how would you like me to proceed?
The implementation is not an iterator: instead, it returns numpy arrays for Xs and Ys.