Time for action – drawing the physics world into the Canvas

Carry out the following steps to draw the useful debug view:

1. First, open the box2dcargame.js JavaScript file:

   var shouldDrawDebug = false;

2. Add a function that draws the debugging lines:

   function showDebugDraw() {
     shouldDrawDebug = true;
   
     //setup debug draw
     var debugDraw = new b2DebugDraw();
     debugDraw.SetSprite(document.getElementById('game').getContext('2d'));
     debugDraw.SetDrawScale(pxPerMeter);
     debugDraw.SetFillAlpha(0.3);
     debugDraw.SetLineThickness(1.0);
     debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit);
   
     carGame.world.SetDebugDraw(debugDraw);
   
     carGame.world.DrawDebugData();
   }

3. Add a showDebugDraw function call at the end of the initGame method:

   showDebugDraw();

4. Now, reopen the game in a browser, and we should see the outline of the ground body in the canvas, as shown in the following screenshot:
   

What just happened?

We have just defined a method that asks the Box2D engine...