after

function BlitTerrain(surface) {
  this.surface = surface;
  this.sprite = new Blit.Sprite(this.surface, 128, 128, 'images/dirt.jpg');
}

BlitTerrain.prototype.render = function(seconds, map, rect) {
  var width = this.sprite.width;
  var height = this.sprite.height;

  var ox = Math.floor(rect.left / width) * width;
  var oy = Math.floor(rect.top / height) * height;

  for (var y = oy; y < rect.bottom; y += width) {
    for (var x = ox; x < rect.right; x += height) {
      this.sprite.blit(x, y, 0);
    }
  }
};

before

PixiTerrain.prototype.createTile = function(x, y, type, timestamp) {
  var sprite = new PIXI.Sprite(this.availableBaseTextures[type]);
  sprite.timestamp = timestamp;
  sprite.position.set(x, y);
  sprite.width = this.tileSize + 1;
  sprite.height = this.tileSize + 1;
  this.groundContainer.addChild(sprite);
  return sprite;
};

PixiTerrain.prototype.destroyTile = function(tile) {
  tile.parent.removeChild(tile);
};

PixiTerrain.prototype.render = function(seconds, state, rect) {
  this.dustSprites = this.dustSprites.filter(renderDust);

  var tileSize = this.tileSize;
  var left = Math.floor(rect.left / tileSize);
  var top = Math.floor(rect.top / tileSize);
  var right = Math.floor(rect.right / tileSize);
  var bottom = Math.floor(rect.bottom / tileSize);
  var now = Date.now();

  for (var row = top; row <= bottom; row++) {
    for (var col = left; col <= right; col++) {
      var index = col + row * state.mapWidth;
      var tileType = Math.floor(Math.random() * this.availableBaseTextures.length); //state.map[index];
      var exists = this.tiles[index];
      if (exists) {
        this.tiles[index].timestamp = now;
      }
      else {
        this.tiles[index] = this.createTile(col * tileSize, row * tileSize, tileType, now);
      }
    }
  }

  Object.keys(this.tiles).forEach(cullOffscreenTiles.bind(this));

  function cullOffscreenTiles(index) {
    if (this.tiles[index].timestamp < now) {
      this.destroyTile(this.tiles[index]);
      delete this.tiles[index];
    }
  }
};