skip presolve when impulse 0

Author: liabru

src/collision/Resolver.js

@@ -186,24 +186,26 @@ var Resolver = {};
                 contactVertex = contact.vertex;
                 normalImpulse = contact.normalImpulse;
                 tangentImpulse = contact.tangentImpulse;
-                
-                // total impulse from contact
-                impulse.x = (normal.x * normalImpulse) + (tangent.x * tangentImpulse);
-                impulse.y = (normal.y * normalImpulse) + (tangent.y * tangentImpulse);
-                
-                // apply impulse from contact
-                if (!(bodyA.isStatic || bodyA.isSleeping)) {
-                    offset = Vector.sub(contactVertex, bodyA.position, tempA);
-                    bodyA.positionPrev.x += impulse.x * bodyA.inverseMass;
-                    bodyA.positionPrev.y += impulse.y * bodyA.inverseMass;
-                    bodyA.anglePrev += Vector.cross(offset, impulse) * bodyA.inverseInertia;
-                }
 
-                if (!(bodyB.isStatic || bodyB.isSleeping)) {
-                    offset = Vector.sub(contactVertex, bodyB.position, tempA);
-                    bodyB.positionPrev.x -= impulse.x * bodyB.inverseMass;
-                    bodyB.positionPrev.y -= impulse.y * bodyB.inverseMass;
-                    bodyB.anglePrev -= Vector.cross(offset, impulse) * bodyB.inverseInertia;
+                if (normalImpulse !== 0 || tangentImpulse !== 0) {
+                    // total impulse from contact
+                    impulse.x = (normal.x * normalImpulse) + (tangent.x * tangentImpulse);
+                    impulse.y = (normal.y * normalImpulse) + (tangent.y * tangentImpulse);
+                    
+                    // apply impulse from contact
+                    if (!(bodyA.isStatic || bodyA.isSleeping)) {
+                        offset = Vector.sub(contactVertex, bodyA.position, tempA);
+                        bodyA.positionPrev.x += impulse.x * bodyA.inverseMass;
+                        bodyA.positionPrev.y += impulse.y * bodyA.inverseMass;
+                        bodyA.anglePrev += Vector.cross(offset, impulse) * bodyA.inverseInertia;
+                    }
+
+                    if (!(bodyB.isStatic || bodyB.isSleeping)) {
+                        offset = Vector.sub(contactVertex, bodyB.position, tempA);
+                        bodyB.positionPrev.x -= impulse.x * bodyB.inverseMass;
+                        bodyB.positionPrev.y -= impulse.y * bodyB.inverseMass;
+                        bodyB.anglePrev -= Vector.cross(offset, impulse) * bodyB.inverseInertia;
+                    }
                 }
             }
         }