I was recently adjusting the stability of Physaxe, a Haxe 2D Physics Engine, and came up with good results and bug fixes, so I just released 1.2 version. Here's a funny example where you can move the mouse around to modify the gravity. There's currently no gravity-center so it will only change the direction and power of the gravity.

The material used has a very small friction, so it's easy for the blocks to slide on each other.

BTW Physaxe is still lacking joints support, so I'm looking for someone interested in helping on that topic, please write me if you are ;)

And of courses the sources, if you want to play with it :

• install Haxe
• run the command haxelib install physaxe to install the Physaxe library
• copy and save the source code to Test.hx
• run haxe -swf9 test.swf -main Test -lib physaxe to compile it
• have fun !

class Test {

    var root : flash.display.MovieClip;
    var world : phx.World;

    function new(root) {
        this.root = root;
        var w = root.stage.stageWidth;
        var h = root.stage.stageHeight;
        world = new phx.World(new phx.col.AABB(0,0,w,h),new phx.col.SortedList());
        var p0 = phx.Const.DEFAULT_PROPERTIES;
        p0.biasCoef = 0.3;
        p0.maxDist = 2;
        world.sleepEpsilon = 0; // no sleep (gravity can change anytime)
        var floor = new phx.Body(0,0);
        floor.addShape(phx.Shape.makeBox(w,30,0,0));
        floor.addShape(phx.Shape.makeBox(w,30,0,h-30));
        floor.addShape(phx.Shape.makeBox(30,h,0,0));
        floor.addShape(phx.Shape.makeBox(30,h,w-30,0));
        floor.isStatic = true;
        world.addBody(floor);
        var mat = new phx.Material(0,0.3,1);
        for( i in 0...100 ) {
            var points = new Array();
            var size = (10 + Std.random(20)) * 0.7;
            var a = 2 * Math.PI;
            do {
                points.push(new phx.Vector(Math.cos(a) * size,Math.sin(a) * size));
                a -= (Std.random(20) + 5) * 0.1;
            } while( a > 0 );
            var shape = new phx.Body(Std.random(w - 100) + 50,Std.random(h - 100) + 50);
            shape.addShape(new phx.Polygon(points,new phx.Vector(0,0),mat));
            world.addBody(shape);
        }
    }

    function update() {
        var w = root.stage.stageWidth;
        var h = root.stage.stageHeight;
        var xf = (root.mouseX / w) * 2 - 1;
        var yf = (root.mouseY / h) * 2 - 1;
        world.gravity.x = xf * 0.5;
        world.gravity.y = yf * 0.5;
        world.step(1.0,20);
        root.graphics.clear();
        var d = new phx.FlashDraw(root.graphics);
        d.shape.lineSize = 0.5;
        d.staticShape.line = null;
        d.drawWorld(world);
    }

    public static function main() {
        var mc = flash.Lib.current;
        var t = new Test(mc);
        mc.stage.quality = flash.display.StageQuality.MEDIUM;
        mc.addEventListener(flash.events.Event.ENTER_FRAME,function(_) t.update());
    }

}