# Binary Tree maze generation in Javascript

## Maze Creation

Generating a maze using the Binary Tree algorithm in Javascript. This simple method searches in a diagonal bias from the starting corner. This results in simple mazes with long corridors covering the sides opposite to the starting corner.

First we create a Maze object that stores information and is used to set the maze dimensions and directional bias:

``````
function Maze(w, h, bias)
{
this.w = (isNaN(w) || w < 5 || w > 999 ? 20 : w);
this.h = (isNaN(h) || h < 5 || h > 999 ? 20 : h);
this.map = new Array();
for(var mh = 0; mh < h; ++mh) { this.map[mh] = new Array(); for(var mw = 0; mw < w; ++mw) { this.map[mh][mw] = {'n':0,'s':0,'e':0,'w':0}; } }

var bias = (typeof bias=='undefined' || (bias!='ne' && bias!='nw' && bias!='sw' && bias!='se') ? 'nw' : bias);

this.build(bias);
}

``````

We then use a method to randomly move to one of the biased direction from each square until we've covered the whole map:

``````
Maze.prototype.build = function(dir)
{
if(typeof dir=='undefined' || (dir!='nw' && dir!='ne' && dir!='sw' && dir!='se')) { dir = 'se'; }

var dirs = new Array();
dirs.push(dir=='ne' || dir=='nw' ? 'n' : 's');
dirs.push(dir=='ne' || dir=='se' ? 'e' : 'w');

for(var y = 0; y < this.h; ++y)
{
var trueY = (dir=='nw' || dir=='ne' ? this.h-(y+1) : y);

for(var x = 0; x < this.w; ++x)
{
var trueX = (dir=='nw' || dir=='sw' ? this.w-(x+1) : x);
var m = 0;

// If we're at the opposite corners for our movement, break!
if(trueY==0 && dirs[0]=='n' && ((trueX==0 && dirs[1]=='w') || (trueX==(this.w-1) && dirs[1]=='e'))) { break; }
if(trueY==(this.h-1) && dirs[0]=='s' && ((trueX==0 && dirs[1]=='w') || (trueX==(this.w-1) && dirs[1]=='e'))) { break; }

// If we're at an opposite border, move the only way we can...
if(trueY==0 && dirs[0]=='n') { this.map[trueY][trueX][dirs[1]] = 1; this.map[trueY][(trueX+(dirs[1]=='w'?-1:1))][(dirs[1]=='w'?'e':'w')] = 1; m = 1; }
else if(trueY==(this.h-1) && dirs[0]=='s') { this.map[trueY][trueX][dirs[1]] = 1; this.map[trueY][(trueX+(dirs[1]=='w'?-1:1))][(dirs[1]=='w'?'e':'w')] = 1; m = 1; }
else if(trueX==0 && dirs[1]=='w') { this.map[trueY][trueX][dirs[0]] = 1; this.map[(trueY+(dirs[0]=='n'?-1:1))][trueX][(dirs[0]=='n'?'s':'n')] = 1; m = 1; }
else if(trueX==(this.w-1) && dirs[1]=='e') { this.map[trueY][trueX][dirs[0]] = 1; this.map[(trueY+(dirs[0]=='n'?-1:1))][trueX][(dirs[0]=='n'?'s':'n')] = 1; m = 1; }

if(m==0)
{
var mov = dirs[Math.floor((Math.random()*1000)%2)];

if(mov=='n') { this.map[trueY][trueX][mov] = 1; this.map[(trueY-1)][trueX]['s'] = 1; }
else if(mov=='s') { this.map[trueY][trueX][mov] = 1; this.map[(trueY+1)][trueX]['n'] = 1; }
else if(mov=='w') { this.map[trueY][trueX][mov] = 1; this.map[trueY][(trueX-1)]['e'] = 1; }
else if(mov=='e') { this.map[trueY][trueX][mov] = 1; this.map[trueY][(trueX+1)]['w'] = 1; }
}
}
}

this.toGrid();
};

``````

And additionally we use a method to convert the map and walls to a useable grid for tile maps:

``````
Maze.prototype.toGrid = function()
{
var grid = new Array();
for(var mh = 0; mh < (this.h * 2 + 1); ++mh) { grid[mh] = new Array(); for(var mw = 0; mw < (this.w * 2 + 1); ++mw) { grid[mh][mw] = 0; } }

for(var y = 0; y < this.h; ++ y)
{
var py = (y * 2) + 1;

for(var x = 0; x < this.w; ++x)
{
var px = (x * 2) + 1;

grid[py][px] = 1;

if(this.map[y][x]['n']==1) { grid[(py-1)][px] = 1; }
if(this.map[y][x]['s']==1) { grid[(py+1)][px] = 1; }
if(this.map[y][x]['e']==1) { grid[py][(px+1)] = 1; }
if(this.map[y][x]['w']==1) { grid[py][(px-1)] = 1; }
}
}

this.gridMap = grid;
this.gridW	= grid.length;
this.gridH	= grid[0].length;
};

``````