the player can't walk through walls

player.js

@@ -1,31 +1,49 @@
 function Player() {
   this._x = 30;
   this._y = 30;
+  this._radius = 15;
   this._moveDistance = 5;
   this._moveTime = 200;
-  this._avatar = Game.world.grantAvatar(this._x, this._y);
+  this._avatar = Game.world.grantAvatar(this._x, this._y, this._radius);
+
+  this.left = function() {
+    return this._x - this._radius;
+  }
+  this.right = function() {
+    return this._x + this._radius;
+  }
+  this.top = function() {
+    return this._y - this._radius;
+  }
+  this.bottom = function() {
+    return this._y + this._radius;
+  }
+
+  this.signal = function(event) {
+    $(this._avatar.node).trigger('player:' + event, this);
+  }
 
   this.moveLeft = function() {
     this._x -= this._moveDistance;
     this._avatar.animate({ cx: this._x }, this._moveTime);
-    this._avatar.node.trigger('player:moveleft')
+    this.signal('move');
   }
 
   this.moveRight = function() {
     this._x += this._moveDistance;
     this._avatar.animate({ cx: this._x }, this._moveTime);
-    this._avatar.node.trigger('player:moveright')
+    this.signal('move');
   }
 
   this.moveUp = function() {
     this._y -= this._moveDistance;
     this._avatar.animate({ cy: this._y }, this._moveTime);
-    this._avatar.node.trigger('player:moveup')
+    this.signal('move');
   }
 
   this.moveDown = function() {
     this._y += this._moveDistance;
     this._avatar.animate({ cy: this._y }, this._moveTime);
-    this._avatar.node.trigger('player:movedown')
+    this.signal('move');
   }
 };

world.js

@@ -3,7 +3,22 @@ function World() {
   this._height = 400;
   this._tile = Raphael('game_window', this._width, this._height);
 
-  this.grantAvatar = function(x, y) {
-    return this._tile.circle(x, y, 15);
+  this.grantAvatar = function(x, y, radius) {
+    return this._tile.circle(x, y, radius);
   }
-};
+
+  this.monitor = function(event, callback) {
+    $(this._tile.canvas).bind(event, callback);
+  }
+
+  this.monitor('player:move', function(event, player) {
+    if (player.left() < 0)
+      player.moveRight();
+    if (player.right() > this._width)
+      player.moveLeft();
+    if (player.top() < 0)
+      player.moveDown();
+    if (player.bottom() > this._height)
+      player.moveUp();
+  })
+}