generalrelativity

Here’s a demo of the auto-gen physics engine (SLRBS- Super Lightweight Rigid Body Simulator) I’ve been working on which allows you to select images to use as rigid bodies. First, the image is analyzed, ignoring transparent pixels, to determine its convex hull. Then mass/center of mass/inertia tensor are solved for. Finally, the rigid body is created and dropped into the world.

I’m sure that in playing with it, you’ll notice all sorts of wonky behavior… but I think it’s fun anyway. Let me know if there’s a class or type of shape/image that tends to be particularly misbehaved!

demo
image pack

drew ActionScript 3.0, Flash Player 10, Geometry, Mathematics, Physics

This was something I did a while ago and never got around to posting about. It’s a simulation of an incompressible fluid- when you render the density and apply temperature by adding an upward force, it looks like smoke!

It’s fairly computationally intensive. The state of the system has to be solved simultaneously. But because it uses an iterative solver to approximate a solution, it’s easy to tune for performance to realism.

Click and drag to knock the smoke around, release to add density (more smoke).

My implementation is based on this paper by Joe Stam. The leap from the Navier Stokes equations to this compact form is pretty radical. Mr. Stam’s a pretty smart guy.

drew ActionScript 3.0, Mathematics, Physics

For the past few months I’ve been working on a general purpose geometry library for representing your interactive elements in a more precise geometrical way. There are some pretty cool features like collision detection management, auto-generation of geometry, and an easy way to bind the model to your DisplayObject hierarchy (or not!). 

It will be released under the MIT license alongside SLRBS- a physics engine that uses the library. The absolute last thing the Flash world needs is another physics engine, but this has some really nice features for beginner developers, prototypers etc. And it does a great job of showing how to use the geometry library.

One of the most frequent questions or requests I get/got with FOAM was something along the lines of “how do I make my MovieClip a rigid body?” It can be hard from my position to know how to tell someone who probably uses the Flash authoring tool a proper way to handle the difference between the model and view. So with SLRBS, I set out to address this issue.

With SLRBS, you have a typical API to create physics simulation, but it also has some streamlined auto-creation methods that make setting it up a breeze. To ensure this, I even downloaded a copy of Flash CS4 to play with it!!! AAAAHH!!! wtf happened to Flash!? 

So, all you do is lay out your MovieClips on the stage, and call a single static method and voila! physics simulation! There’s some pretty cool stuff going on that determine how to handle overlapping DisplayObjects (each demo does it differently), and it’s just a single parameter.

Here’s a screenshot of the stage in a demo where a car is being created:

Car Demo

Because 2 of the tires overlap the car, they get pinned to the car at their center of mass.

This is the only ActionScript in the .fla:

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import org.generalrelativity.slrbs.SLRBSimulator;
 
var simulator:SLRBSimulator = SLRBSimulator.createSLRBSimulatorFromContainer( this );
addEventListener( Event.ENTER_FRAME, onEnterFrame );
 
function onEnterFrame( event:Event ) : void
{
   simulator.step( 1 / 60 );
}

Here’s a second demo’s stage in the Flash authoring tool- this time a ragdoll. The overlap this time gets pinned at the center of overlap instead of the center of mass as in the car demo- this works well for creating ragdoll joints.

Ragdoll Demo

drew ActionScript 3.0, Flash Player 10, Mathematics, Physics