update body velocity properties after resolving

src/body/Body.js

@@ -747,10 +747,6 @@ var Axes = require('../geometry/Axes');
         body.anglePrev = body.angle;
         body.angle += body.angularVelocity;
 
-        // track speed and acceleration
-        body.speed = Vector.magnitude(body.velocity);
-        body.angularSpeed = Math.abs(body.angularVelocity);
-
         // transform the body geometry
         for (var i = 0; i < body.parts.length; i++) {
             var part = body.parts[i];
@@ -774,6 +770,23 @@ var Axes = require('../geometry/Axes');
         }
     };
 
+    /**
+     * Updates properties `body.velocity`, `body.speed`, `body.angularVelocity` and `body.angularSpeed`.
+     * @method updateVelocities
+     * @param {body} body
+     */
+    Body.updateVelocities = function(body) {
+        var timeScale = Common._timeUnit / body.deltaTime,
+            bodyVelocity = body.velocity;
+
+        bodyVelocity.x = (body.position.x - body.positionPrev.x) * timeScale;
+        bodyVelocity.y = (body.position.y - body.positionPrev.y) * timeScale;
+        body.speed = Math.sqrt((bodyVelocity.x * bodyVelocity.x) + (bodyVelocity.y * bodyVelocity.y));
+
+        body.angularVelocity = (body.angle - body.anglePrev) * timeScale;
+        body.angularSpeed = Math.abs(body.angularVelocity);
+    };
+
     /**
      * Applies a force to a body from a given world-space position, including resulting torque.
      * @method applyForce

src/core/Engine.js

@@ -171,6 +171,9 @@ var Body = require('../body/Body');
             Resolver.solveVelocity(pairs.list, delta);
         }
 
+        // update body speed and velocity properties
+        Engine._bodiesUpdateVelocities(allBodies);
+
         // trigger collision events
         if (pairs.collisionActive.length > 0)
             Events.trigger(engine, 'collisionActive', { pairs: pairs.collisionActive });
@@ -284,6 +287,20 @@ var Body = require('../body/Body');
         }
     };
 
+    /**
+     * Applies `Body.updateVelocities` to all given `bodies`.
+     * @method _bodiesUpdate
+     * @private
+     * @param {body[]} bodies
+     */
+    Engine._bodiesUpdateVelocities = function(bodies) {
+        var bodiesLength = bodies.length;
+
+        for (var i = 0; i < bodiesLength; i++) {
+            Body.updateVelocities(bodies[i]);
+        }
+    };
+
     /**
      * A deprecated alias for `Runner.run`, use `Matter.Runner.run(engine)` instead and see `Matter.Runner` for more information.
      * @deprecated use Matter.Runner.run(engine) instead

src/render/Render.js

@@ -10,7 +10,6 @@ var Render = {};
 
 module.exports = Render;
 
-var Body = require('../body/Body');
 var Common = require('../core/Common');
 var Composite = require('../body/Composite');
 var Bounds = require('../geometry/Bounds');
@@ -1107,10 +1106,8 @@ var Mouse = require('../core/Mouse');
             if (!body.render.visible)
                 continue;
 
-            var velocity = Body.getVelocity(body);
-
             c.moveTo(body.position.x, body.position.y);
-            c.lineTo(body.position.x + velocity.x * 2, body.position.y + velocity.y * 2);
+            c.lineTo(body.position.x + body.velocity.x * 2, body.position.y + body.velocity.y * 2);
         }
 
         c.lineWidth = 3;