first attempt of implmenting asm style box2d engine

app/Lib/Vendor/Box2D/helpers.js

@@ -0,0 +1,106 @@
+define([
+    "Lib/Vendor/Box2D/asmBox2d"
+],
+ 
+function () {
+
+    //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.
+    var using = function (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);
+        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);
+    }
+
+    return {
+        createPolygonShape: createPolygonShape,
+        createChainShape: createChainShape,
+        createRandomPolygonShape: createRandomPolygonShape,
+        scaleVec2: scaleVec2,
+        scaledVec2: scaledVec2,
+        copyVec2: copyVec2,
+        using: using
+    };
+});