Truchet tiles are an easy way to generate unexpected image patterns from tiling a surface with the same repeating image that is simply rotated with a multiple of 90 degrees. You can choose to rotate the new tile with a given pattern (let’s say one rotation every 3 tile), or let randomness choose.
Here is an example with the elementary cell being a triangle, paving a 10 x 10 surface :
In the above, the rotating pattern from one tiling to the next is to rotate two tiles out of three (0, -90°, -90°), going from left to right and top to bottom.
You can also try with different elementary shapes. Here’s a classic example with the elementary cell consisting of a blue quare with two 90° white arcs in the opposite corners :
I find it a good exercise to get started with object oriented programming in Processing, and encourage you to download this code (the triangles example) and hack it to generate your own patterns :