gistfile1.js

// add tile
    ig.game.addItem({
        _layer : 'bg',
        update: function(){
            var mainMap = ig.game.getMapByName('main'),
                tileSize = mainMain.tilesize,
                ctx = ig.game.bgCanvasContext,
                x = tileSize * x * ig.system.scale,
                y = tileSize * y * ig.system.scale;

            ctx.save();
            ctx.fillStyle = 'tan';
            ctx.fillRect(x,y,tileSize,tileSize);
            ctx.restore();
        },
        draw:function(){
            // empty the array we dont want to draw anything with these objects
            ig.game.layers[this._layer] = [];
        }
    });

// remove tile
    ig.game.addItem({
        _layer : 'bg',
        update: function(){
            var mainMap = ig.game.getMapByName('main'),
                tileSize = mainMain.tilesize,
                ctx = ig.game.bgCanvasContext,
                x = tileSize * x * ig.system.scale,
                y = tileSize * y * ig.system.scale;

            ctx.save();
            ctx.clearRect(x,y,tileSize,tileSize);
            ctx.restore();
        },
        draw:function(){
            // empty the array we dont want to draw anything with these objects
            ig.game.layers[this._layer] = [];
        }
    });