新增flag 帮助处理位掩码

source/src/Physics/Shapes/Circle.ts

@@ -0,0 +1,11 @@
+///<reference path="./Shape.ts" />
+class Circle extends Shape {
+    public radius: number;
+    private _originalRadius: number;
+
+    constructor(radius: number){
+        super();
+        this.radius = radius;
+        this._originalRadius = radius;
+    }
+}