embox2d-helpers.js

//Having to type 'Box2D.' in front of everything makes porting
//existing C++ code a pain in the butt. This function can be used
//to make everything in the Box2D namespace available without
//needing to do that.
function using(ns, pattern) {    
    if (pattern == undefined) {
        // import all
        for (var name in ns) {
            this[name] = ns[name];
        }
    } else {
        if (typeof(pattern) == 'string') {
            pattern = new RegExp(pattern);
        }
        // import only stuff matching given pattern
        for (var name in ns) {
            if (name.match(pattern)) {
                this[name] = ns[name];
            }
        }       
    }
}
    
var e_shapeBit = 0x0001;
var e_jointBit = 0x0002;
var e_aabbBit = 0x0004;
var e_pairBit = 0x0008;
var e_centerOfMassBit = 0x0010;


//to replace original C++ operator =
function copyVec2(vec) {
    return new b2Vec2(vec.get_x(), vec.get_y());
}

//to replace original C++ operator * (float)
function scaleVec2(vec, scale) {
    vec.set_x( scale * vec.get_x() );
    vec.set_y( scale * vec.get_y() );            
}

//to replace original C++ operator *= (float)
function scaledVec2(vec, scale) {
    return new b2Vec2(scale * vec.get_x(), scale * vec.get_y());
}


// http://stackoverflow.com/questions/12792486/emscripten-bindings-how-to-create-an-accessible-c-c-array-from-javascript
function createChainShape(vertices, closedLoop) {
    var shape = new b2ChainShape();            
    var buffer = Box2D.allocate(vertices.length * 8, 'float', Box2D.ALLOC_STACK);
    var offset = 0;
    for (var i=0;i<vertices.length;i++) {
        Box2D.setValue(buffer+(offset), vertices[i].get_x(), 'float'); // x
        Box2D.setValue(buffer+(offset+4), vertices[i].get_y(), 'float'); // y
        offset += 8;
    }            
    var ptr_wrapped = Box2D.wrapPointer(buffer, Box2D.b2Vec2);
    if ( closedLoop )
        shape.CreateLoop(ptr_wrapped, vertices.length);
    else
        shape.CreateChain(ptr_wrapped, vertices.length);
    return shape;
}

function createPolygonShape(vertices) {
    var shape = new b2PolygonShape();            
    var buffer = Box2D.allocate(vertices.length * 8, 'float', Box2D.ALLOC_STACK);
    var offset = 0;
    for (var i=0;i<vertices.length;i++) {
        Box2D.setValue(buffer+(offset), vertices[i].get_x(), 'float'); // x
        Box2D.setValue(buffer+(offset+4), vertices[i].get_y(), 'float'); // y
        offset += 8;
    }            
    var ptr_wrapped = Box2D.wrapPointer(buffer, Box2D.b2Vec2);
    shape.Set(ptr_wrapped, vertices.length);
	for (var i in vertices){
		Box2D.destroy(vertices[i]);
		}
    return shape;
}
 function createEdgeShape(vertices){
	var shape=new b2EdgeShape();
	var buffer=Box2D.allocate(vertices.length * 8,'float',Box2D.ALLOC_STACK);
	var offset =0;
	for (var i=0;i<vertices.legth;i++){
		Box2D.setValue(buffer+(offset),vertices[i].get_x(),'float');
		Box2D.setValue(buffer+(offset+4),vertices[i].get_y(),'float');
		offset+=8;
	}
	var ptr_wrapped =Box2D.wrapPointer(buffer,Box2D.b2Vec2);
	shape.Set(ptr_wrapped,vertices.length);
	for(var i in vertices){
		//Box2D.destroy(vertices[i]);
		}
	return shape;
	}
function createRandomPolygonShape(radius) {
    var numVerts = 3.5 + Math.random() * 5;
    numVerts = numVerts | 0;
    var verts = [];
    for (var i = 0; i < numVerts; i++) {
        var angle = i / numVerts * 360.0 * 0.0174532925199432957;
        verts.push( new b2Vec2( radius * Math.sin(angle), radius * -Math.cos(angle) ) );
    }            
    return createPolygonShape(verts);
}

function getPosition(vert1,vert2) {
	var position = new b2Vec2(0,0);
	position.set_x(0.5 *(vert1.get_x()+vert2.get_x()));
	position.set_y(0.5 *(vert1.get_y()+vert2.get_y()));
	//Box2D.destroy(position);
	//console.log('x : '+position.get_x() + 'y :' +position.get_y());
	return position;
	}
	
function getDistance(vert1,vert2){
    //console.log(vert2);
	var resultantVector= new b2Vec2(vert2.get_x()-vert1.get_x(),vert2.get_y()-vert1.get_y());
	var distance = resultantVector.Length();
	Box2D.destroy(resultantVector);
	return distance;
	}

function getAngle(vert1,vert2){
	var resultantVector = new b2Vec2(vert2.get_x()-vert1.get_x(),vert2.get_y()-vert1.get_y());
	var angle = Math.atan2(resultantVector.get_y(),resultantVector.get_x());
	Box2D.destroy(resultantVector);
	return angle;
	}
	
function getRandomColor() {
    var letters = '0123456789ABCDEF'.split('');
    var color = '#';
    for (var i = 0; i < 6; i++ ) {
        color += letters[Math.floor(Math.random() * 16)];
    }
    return color;
}

var setContactListener = function(){
console.log('entered');
	myContactListener = new b2ContactListener();
	Box2D.customizeVTable(myContactListener,[{
		original : Box2D.b2ContactListener.prototype.BeginContact,
		replacement : function(thsPtr,contactPtr){
							var contact = Box2D.wrapPointer(contactPtr,b2Contact);
							var body1 = contact.GetFixtureA().GetBody();
							var body2 = contact.GetFixtureB().GetBody();
							// console.log(body1.a +'   ' + body2.a);
							//console.log('listener');
							//console.log(' body1 ' + body1.userData.id +' body2 ' +body2.userData.id);
							
							if(body1.userData.id == 'ball' && body2.userData.id == 'star'){
								to_be_destroyed = body2.a;
								//console.log(to_be_destroyed);
								}
							else if(body1.userData.id == 'star' && body2.userData.id == 'ball'){
								to_be_destroyed = body1.a;
								}
			          }
			}])
		world.SetContactListener(myContactListener);
		}