Box2D Forums

Hi! I'm starting working with Box2D on Flash platform. I choose it cause i need to do such a thing: a circle with the small car inside of it, we can change the circle radius, car speed (force?) and car mass; then if the speed is to small the car will not reach the top of the circle and will fall down. All I need to know is if it possible to do using Box2D and if it is, how to create a circle in which a car will drive? It must be created like a physics container or like a shape? Thank you for help.

Is nobody really know if it is possible? If you know that it-s impossible just write me. But if it is please say how to create such a thing.

You could make a ring of polygons or edge shapes.
It might be tricky to change the size of the ring, but I guess if you are only concerned about the interior of the ring for your game, you could make each segment very long and move them all inwards or outwards to change the size.

Irresistible force has the right idea here, just use something like this to add edges to a body:


var radius:Number = 100;
var numSegments:Number = 24;
var twoPi:Number = Math.PI * 2;

for ( var ct:int = 0 ; ct < numSegments ; ct++) {

addVertex( Math.cos( (ct / numSegments) * twoPi) * radius , Math.sin( ct/numSegments * twoPi) * radius );

}

You might need to add the edges back-to-front, but that should do it.