added engine beforeSolve event, closes #1173

src/core/Engine.js

@@ -72,7 +72,7 @@ var Body = require('../body/Body');
 
     /**
      * Moves the simulation forward in time by `delta` milliseconds.
-     * Triggers `beforeUpdate` and `afterUpdate` events.
+     * Triggers `beforeUpdate`, `beforeSolve` and `afterUpdate` events.
      * Triggers `collisionStart`, `collisionActive` and `collisionEnd` events.
      * @method update
      * @param {engine} engine
@@ -128,6 +128,8 @@ var Body = require('../body/Body');
             Engine._bodiesUpdate(allBodies, delta);
         }
 
+        Events.trigger(engine, 'beforeSolve', event);
+
         // update all constraints (first pass)
         Constraint.preSolveAll(allBodies);
         for (i = 0; i < engine.constraintIterations; i++) {
@@ -327,6 +329,17 @@ var Body = require('../body/Body');
     * @param {string} event.name The name of the event
     */
 
+    /**
+    * Fired after bodies updated based on their velocity and forces, but before any collision detection, constraints and resolving etc.
+    *
+    * @event beforeSolve
+    * @param {object} event An event object
+    * @param {number} event.timestamp The engine.timing.timestamp of the event
+    * @param {number} event.delta The delta time in milliseconds value used in the update
+    * @param {engine} event.source The source object of the event
+    * @param {string} event.name The name of the event
+    */
+
     /**
     * Fired after engine update and all collision events
     *