Emanuele Feronato

Talking about Box2D, Game development, HTML5, Javascript and Phaser.

Back in 2008 I blogged about the magic of compound objects with Box2D to create complex shapes, and eventually built a game upon this concept, called MazeRoll.

Now it’s time to do the same thing with Phaser, building a maze in a single body.

The maze is built with the same script used in Pure JavaScript perfect tile maze generation – with a bit of magic thanks to Phaser, have a look at it:

Try to drag the mouse, you will see it’s a single body made with more fixtures.

Everything runs around the creation of a body with no fixtures – think about it as an empty body – with rectangular fixtures added to it at runtime with addRectangle method.

addRectangle(width, height, offsetX, offsetY, rotation)

Adds a Rectangle fixture to a Body. You can control the offset from the center of the body and the rotation. It will use the World friction, restitution and density by default.

This is the source code.

var game;
var maze = [];
var mazeWidth = 15; // maze width, in tiles. Should be odd
var mazeHeight = 11; // maze height, in tiles. Should be odd
var cellSize = 30;

window.onload = function() {	
	game = new Phaser.Game(640, 480, Phaser.AUTO, "");
     game.state.add("PlayGame",playGame);
     game.state.start("PlayGame");
}
	
var playGame = function(game){};

playGame.prototype = {
  	create: function(){
  		game.stage.backgroundColor = "#222222";
  		// in the same way we initialized other Phaser physics engines, this is how we initialize Box2D engine
		game.physics.startSystem(Phaser.Physics.BOX2D);
		// setting gravity
		game.physics.box2d.gravity.y = 500;
		// adding a ground static body
    		var groundBody = new Phaser.Physics.Box2D.Body(game, null, 0, 0, 0);
          // adding a rectangle fixture to the body
          groundBody.addRectangle(640, 20, game.width/2, game.height-10); 
    		// waiting for player input
    		game.input.onDown.add(mouseDragStart, this);
          game.input.addMoveCallback(mouseDragMove, this);
          game.input.onUp.add(mouseDragEnd, this);
          //var box2d = new Phaser.Physics.Box2D(game);
          var mazeBody = new Phaser.Physics.Box2D.Body(game, null, game.width/2-mazeWidth*cellSize/2, 0, 2);
          // creation of the maze itself
          createMaze();
          for(var i = 0; i < mazeHeight; i ++){
               for(var j = 0; j < mazeWidth; j ++){
                    if(maze[i][j]){
                         // adding maze bricks
                         mazeBody.addRectangle(cellSize, cellSize, cellSize * j, cellSize * i)     
                    }
               }
          }
	},
     render: function(){
          // this is the debug draw in action
          game.debug.box2dWorld();
     }
}

function mouseDragStart() {
     game.physics.box2d.mouseDragStart(game.input.mousePointer);    
}

function mouseDragMove() {
     game.physics.box2d.mouseDragMove(game.input.mousePointer);    
}

function mouseDragEnd() {
    game.physics.box2d.mouseDragEnd();    
}

function createMaze(){
     var moves = [];
     for(var i = 0; i < mazeHeight; i ++){
          maze[i] = [];
          for(var j = 0; j < mazeWidth; j ++){
               maze[i][j] = 1;
          }
     }
     var posX = 1;
     var posY = 1;
     maze[posX][posY] = 0; 
     moves.push(posY + posY * mazeWidth);
     while(moves.length){       
          var possibleDirections = "";
          if(posX+2 > 0 && posX + 2 < mazeHeight - 1 && maze[posX + 2][posY] == 1){
               possibleDirections += "S";
          }
          if(posX-2 > 0 && posX - 2 < mazeHeight - 1 && maze[posX - 2][posY] == 1){
               possibleDirections += "N";
          }
          if(posY-2 > 0 && posY - 2 < mazeWidth - 1 && maze[posX][posY - 2] == 1){
               possibleDirections += "W";
          }
          if(posY+2 > 0 && posY + 2 < mazeWidth - 1 && maze[posX][posY + 2] == 1){
               possibleDirections += "E";
          } 
          if(possibleDirections){
               var move = game.rnd.between(0, possibleDirections.length - 1);
               switch (possibleDirections[move]){
                    case "N": 
                         maze[posX - 2][posY] = 0;
                         maze[posX - 1][posY] = 0;
                         posX -= 2;
                         break;
                    case "S":
                         maze[posX + 2][posY] = 0;
                         maze[posX + 1][posY] = 0;
                         posX += 2;
                         break;
                    case "W":
                         maze[posX][posY - 2] = 0;
                         maze[posX][posY - 1] = 0;
                         posY -= 2;
                         break;
                    case "E":
                         maze[posX][posY + 2]=0;
                         maze[posX][posY + 1]=0;
                         posY += 2;
                         break;         
               }
               moves.push(posY + posX * mazeWidth);     
          }
          else{
               var back = moves.pop();
               posX = Math.floor(back / mazeWidth);
               posY = back % mazeWidth;
          }                                 
     }      
}

And this is how you can create compound objects with Box2D and Phaser. Next time, I will port my MazeRoll game in HTML5, meanwhile download the source code.