Question

I’ve been doing some Googling to find an answer to this, but I’ve had no luck. It could be because I’m a bit of an amateur and I don’t know the proper terms to search for, but maybe someone here can steer me in the right direction or help me out.

Anyway, I’m looking for a way to get a div to randomly, smoothly move around a page. There will be a background color, then this image which I want to seemingly randomly, infinitely move around the page. Much like the background of a DVD player’s home screen where “DVD” is just floating around.

Starting point of the div doesn’t matter, nor does the ending point. It just needs to randomly move around the page for the duration a user is on that page.

I’ve got decent HTML and CSS skills, very basic JS skills, and some experience implementing jQuery. Ideally, I’d like something which I can implement myself.

Thanks in advance!!!

Answer 1

The basic premise is to generate positional values, and use jquery’s animate() function to move the div. The calculation of the next position is simple, you just need a bit of math. Here’s a very basic jsfiddle i just knocked up. It could do with possibly a delay timer, a dynamically calculating speed based on how far its got too move e.c.t. But it gives you a start point i hope.

http://jsfiddle.net/Xw29r/

Updated example code with speed modifier:

http://jsfiddle.net/Xw29r/15/

---

For some reason this is still getting some attention, so here’s an updated answer that uses CSS transitions which should be much smoother.

http://jsfiddle.net/bf9nv1q6/

function RandomObjectMover(obj, container) {
	this.$object = obj;
  this.$container = container;
  this.container_is_window = container === window;
  this.pixels_per_second = 250;
  this.current_position = { x: 0, y: 0 };
  this.is_running = false;
}

// Set the speed of movement in Pixels per Second.
RandomObjectMover.prototype.setSpeed = function(pxPerSec) {
	this.pixels_per_second = pxPerSec;
}

RandomObjectMover.prototype._getContainerDimensions = function() {
   if (this.$container === window) {
       return { 'height' : this.$container.innerHeight, 'width' : this.$container.innerWidth };
   } else {
   	   return { 'height' : this.$container.clientHeight, 'width' : this.$container.clientWidth };
   }
}

RandomObjectMover.prototype._generateNewPosition = function() {

	// Get container dimensions minus div size
  var containerSize = this._getContainerDimensions();
	var availableHeight = containerSize.height - this.$object.clientHeight;
  var availableWidth = containerSize.width - this.$object.clientHeight;
    
  // Pick a random place in the space
  var y = Math.floor(Math.random() * availableHeight);
  var x = Math.floor(Math.random() * availableWidth);
    
  return { x: x, y: y };    
}

RandomObjectMover.prototype._calcDelta = function(a, b) {
	var dx   = a.x - b.x;         
  var dy   = a.y - b.y;         
  var dist = Math.sqrt( dx*dx + dy*dy ); 
  return dist;
}

RandomObjectMover.prototype._moveOnce = function() {
		// Pick a new spot on the page
    var next = this._generateNewPosition();
    
    // How far do we have to move?
    var delta = this._calcDelta(this.current_position, next);
    
		// Speed of this transition, rounded to 2DP
		var speed = Math.round((delta / this.pixels_per_second) * 100) / 100;
    
    //console.log(this.current_position, next, delta, speed);
          
    this.$object.style.transition='transform '+speed+'s linear';
    this.$object.style.transform='translate3d('+next.x+'px, '+next.y+'px, 0)';
    
    // Save this new position ready for the next call.
    this.current_position = next;
  
};

RandomObjectMover.prototype.start = function() {

	if (this.is_running) {
  	return;
  }

	// Make sure our object has the right css set
  this.$object.willChange = 'transform';
  this.$object.pointerEvents = 'auto';
	
  this.boundEvent = this._moveOnce.bind(this)
  
  // Bind callback to keep things moving
  this.$object.addEventListener('transitionend', this.boundEvent);
  
  // Start it moving
  this._moveOnce();
  
  this.is_running = true;
}

RandomObjectMover.prototype.stop = function() {

	if (!this.is_running) {
  	return;
  }
  
  this.$object.removeEventListener('transitionend', this.boundEvent);
  
	this.is_running = false;
}


// Init it
var x = new RandomObjectMover(document.getElementById('a'), window);


// Toolbar stuff
document.getElementById('start').addEventListener('click', function(){
	x.start();
});
document.getElementById('stop').addEventListener('click', function(){
	x.stop();
});
document.getElementById('speed').addEventListener('keyup', function(){
  if (parseInt(this.value) > 3000 ) {
 		alert('Don\'t be stupid, stupid');
    this.value = 250;
  }
	x.setSpeed(parseInt(this.value));
});


// Start it off

x.start();

div#toolbar {
  position:fixed;
  background:#20262F;
  width:100%;
  text-align:center;
  padding: 10px
}
div#a {
width: 50px;
height:50px;
background-color:red;
position:absolute;
}

<div id="toolbar">
<button id="start">Start</button>
<button id="stop">Stop</button>
<input type="number" value="250" id="speed" />
</div>
<div id='a'></div>