新增verlet物理引擎（实验性）

source/src/Physics/Verlet/Constraints/AngleConstraint.ts

@@ -0,0 +1,47 @@
+///<reference path="./Constraint.ts" />
+module es {
+    export class AngleConstraint extends Constraint {
+        public stiffness: number;
+        public angleInRadius: number;
+        
+        _particleA: Particle;
+        _centerParticle: Particle;
+        _particleC: Particle;
+
+        constructor(a: Particle, center: Particle, c: Particle, stiffness: number) {
+            super();
+            this._particleA = a;
+            this._centerParticle = center;
+            this._particleC = c;
+            this.stiffness = stiffness;
+
+            this.collidesWithColliders = false;
+
+            this.angleInRadius = this.angleBetweenParticles();
+        }
+
+        angleBetweenParticles(): number {
+            const first = this._particleA.position.sub(this._centerParticle.position);
+            const second = this._particleC.position.sub(this._centerParticle.position);
+
+            return Math.atan2(first.x * second.y - first.y * second.x, first.x * second.x + first.y * second.y);
+        }
+
+        public solve() {
+            const angleBetween = this.angleBetweenParticles();
+            let diff = angleBetween - this.angleInRadius;
+
+            if (diff <= -Math.PI)
+                diff += 2 * Math.PI;
+            else if(diff >= Math.PI)
+                diff -= 2 * Math.PI;
+
+            diff *= this.stiffness;
+
+            this._particleA.position = MathHelper.rotateAround2(this._particleA.position, this._centerParticle.position, diff);
+            this._particleC.position = MathHelper.rotateAround2(this._particleC.position, this._centerParticle.position, -diff);
+            this._centerParticle.position = MathHelper.rotateAround2(this._centerParticle.position, this._particleA.position, diff);
+            this._centerParticle.position = MathHelper.rotateAround2(this._centerParticle.position, this._particleC.position, -diff);
+        }
+    }
+}