Poisson Disk Sampling Example Code

poissonI decided to put the Poisson disk sampling code here for download since the site that hosted it is down. The code accompanies the tutorial on Dev.Mag: Poisson Disk Sampling.


poisson_disk_java.zip (184 KB)
poisson_disk_python.zip (912 KB)
poisson_disk_ruby.zip (59 KB)

Getting More out of Seamless Tiles

tiles_header_smallI wrote an article for Dev.Mag covering some techniques for working with seamless tile sets such as making blend tiles, getting more variety with procedural colour  manipulation, tile placement strategies, and so on. 

Check it out!

The Python Image Code has also been updated with some of the algorithms explained in the article.

Generating Random Integers With Arbitrary Probabilities


I finally laid my hands on Donald Knuth’s The Art of Computer Programming (what a wonderful set of books!), and found a neat algorithm for generating random integers 0, 1, 2, … , n – 1, with probabilities p_0, p_1, … , p_(n-1).

I have written about generating random numbers (floats) with arbitrary distributions for one dimension and higher dimensions, and indeed that method can be adapted for generating integers with specific probabilities. However, the method described below is much more concise, and efficient (I would guess) for this special case. Moreover, it is also easy to adapt it to generate floats for continuous distributions.

Continue reading “Generating Random Integers With Arbitrary Probabilities”

How to Turn XSI Mod Tool into a Level Editor for your XNA Games: Updated for XNA 3.0.


Last year I wrote a tutorial explaining how to use XSI Mod Tool as a level editor, specifically for XNA. Below is the same tutorial, updated for XNA 3.0. There are only a few minor changes:

  • You need not copy compiled assets from the batch file as before.
  • A section is included that describes how to use the content pipeline classes for easy reading of XML files (useful for level files, etc.).

I also corrected quite a few typos.
Continue reading “How to Turn XSI Mod Tool into a Level Editor for your XNA Games: Updated for XNA 3.0.”


The code below implements some quadtree extensions, as discussed in another Dev.Mag tutorial about quadtrees (see Issue 27). The tutorial covers the following topics:

  • what to consider in choosing whether to use a quadtree or not;
  • tests to help you choose an appropriate threshold;
  • how to handle discrete data; and
  • some modifications to the basic algorithm.

Handling Discrete Data

When it comes to discrete data, the “average” of a number of pixels doesn’t make sense. However, we can give it meaning and still use it to get good approximations of the original data, as illustrated in the images below.

The original grid of discrete data. The grid contains integers from 0 to 4. Every integer is mapped to a colour in this image. (If this grid represented a tile map, every integer would be mapped to a different tile).
Here we allowed floating point numbers in the quadtree. Results of queries into the quadtree are rounded before mapping them to colours.
Here we used the floating point part of queries to bias a randomly selected integer. For example, a result of 1.25 will result in a 75% chance of yielding 2.
Here we use a quadtree with interpolation. The result is rounded before it is mapped.
Here we use a quadtree with interpolation, and use the floating point part of the number to bias a randomly selected tile, as above.


Python Implementation

Download from: http://code-spot.co.za/python-image-code/ (See quadtree.py, quadtree_image.py, and quadtree_demo.py).


The quadtree is an important 2D data structure and forms the core of many spatial algorithms, including compression, collision detection, and stitching algorithms. Below you can download general purpose quadtree implementations in Java and Python.

The code accompanies the Quadtrees article in Dev.Mag. The tutorial explains how the implement a quadtree that can be use to store 2D data efficiently, lists what considerations there are in real-world applications, and gives some debugging tips.

Channels Compressed Simultaneously

bar bar_c
The original image (by smcgee). The image after being loaded into a quadtree.

Continue reading “Quadtrees”