Rigid-body physics using particles

Lachlan Phillips — Wed, 15 Jan 2014 17:58:07 GMT

Towards the end of last year, I worked on a prototype physics engine based on a GPU Gems chapter --- a realtime physics simulation running on the GPU. So far I've only written it for the CPU as I've never done any GPU work before. (judging by the problems I've had with the physics side of things, it was probably a good idea not to heap on an order of magnitude more GPU problems...)

Here's a video of it in action:

After I managed to get rotation pretty much working' --- it still does odd things --- it worked pretty well. It's operating on the pixel/metre scale, because I was lazy... so everything here is massive skyscraper-sized entities. Quite by accident, it appears to have 'conservation of momentum' --- if I draw a 'C', and fill it with particles it will accelerate like a ~rocket~ snail.

Eventually, I'll work out how to port it to GPU, hook it up with OpenGL, and make it 3D... but that'll be a while.

In the meanwhile, read the code at Github, and... I've not got the build properly set up on Jenkins so you can't download it.

EDIT: another video from some time later:

Growing Trees with Space Colonisation in 2D

Lachlan Phillips — Fri, 06 Sep 2013 01:50:27 GMT

Yesterday, I quickly hacked up an implementation of the Space Colonisation algorithm, for growing trees. By trees, I don't mean the binary trees – the living sort, just represented by segments and forks.

My inspiration was from Procedural World and this article. The idea of Space Colonisation is to colonise/fill a limited area. A tree like this would grow from the bottom up (as they usually do), gradually taking up all the available space. Trees generated by this algorithm (as far as I know) rarely have intersecting branches, and look organic.

I started coding from the top (as usual I didn't plan much beforehand, but it didn't turn out too bad) – a Main class that creates a Point Cloud in a spherical shape, grows a tree in that cloud, and renders the tree out to an image. Later I added a GUI for faster feedback.

After some work, I got this:

The green points are the Point Cloud, and the black dots with the yellow lines are the generated tree (segments).

When I constructed the GUI, I added the option of scaling the point cloud horizontally, which can give me trees like:

Here's a quick shot of the GUI:

I've still got more work to do, things like

Add different point cloud shapes
- Generate from an image?
Support for multiple trees growing in the same space
Biases
- Bias upwards
Rendering more tree-like
- Trunk should be thicker than topmost twigs
- Very close branches could be merged

The code is available on Github.

Lachlan Phillips (Posts about simulation)

Rigid-body physics using particles

Growing Trees with Space Colonisation in 2D