2D pathfinding with raycasting

[DavidBraun]

Processing/GLSL expert Thomas Diewald has written and posted videos about 2D pathfinding and raycasting
thomasdiewald.com/blog/?p=2949
Warning, this first paragraph is about 3D so I’m not sweating the details.

The idea of Global Line Radiosity in 3D is, to compute these Ray-Scene intersections in parallel for the whole scene (global lines) using the rasterizer. The scene is rendered (orthograhic projection) from different directions into a deep framebuffer that stores every single rasterized fragment, not just those that pass the fragment test (DEPTH_TEST), a technique that is also used for OIT (Order Independent Transparency). At each pixel/fragment, the list of frags (sorted by depth) is then used to propagate direct/indirect light. There is lots of room for variations and optimisations in this pipeline, and its a really neat alternative to conventional Raytracing.

But then he writes this:

For 2D-Scenes I am basically using the same algorithm except that rasterization into a deep framebuffer is not even necessary (and also not possible as in 3D).

So I’m thinking for 2D he doesn’t even use an equivalent of a Render TOP and a Camera. A GLSL TOP approach would suffice.
Then he write this
thomasdiewald.com/blog/?p=3250

Random rays are generated for every pixel in the map to gather the shortest distance (+ the current ray length) at the found intersection. The pixel data gets updated if this new distance is shorter then the one currently stored.

Unfortunately, I haven’t figured out what he means by generating rays. I might take some ideas from this thomasdiewald.com/blog/?p=2949) until I find the target or something that has seen the target (or something that has seen something that has seen the target etc.) Early on, plenty of pixels would halt before finding something, but I’d imagine after a few frames there’d be a cascading effect that fills out the distance field. Share your thoughts!

PS. To get a pathfinding result, take a Sobel Filter of the distance field.

Update:
Hooray I got it working mainly thanks to lodev.org/cgtutor/raycasting.html