Simple camera for ROT.js

rotjs_camera.js

// Define a camera XY object 
Game.camera = new XY();

// game draw function:

Game.draw =  function(xy) {
  var entity = this.level.getEntityAt(xy);
  var visual = entity.getVisual();
  this.display.draw(xy.x - this.camera.x, xy.y - this.camera.y, visual.ch, visual.fg, visual.bg);
};

// to move the camera, pass it an XY. For example, the player's XY.
Game.updateCamera = function(xy) {
  // pick an offset x and y that makes sense for your game.
  // you could probably also implement a camera trap here if you wanted to get fancy
  this.camera.x = xy.x - 8;
  this.camera.y = xy.y - 8;
};