Here's a little code snippet for today.

While I was making the 3D CSS Mario Kart, I needed a simple, drop-in bit of code to handle touch interfaces. I looked through some old experiments and found a rough version of the code below. It was based on this KeyboardController by Stack Overflow user Bob Ince.

It doesn't do anything clever. All it does is provide a simple way to attach functionality to touch events in different areas of the screen – top-left, top-center, top-right, middle-left, middle-center, middle-right, bottom-left, bottom-center, bottom-right. My apologies to any Brits for the spelling of centre as 'center'. It's the Internet, we have to.

How to use

Include this code:

function TouchController(areas, repeat) {
  var touchtimer;
  document.onmousedown = document.ontouchstart = document.ontouchmove = function(e) {
    var position;
    e.preventDefault();
    e.touches = [{'clientX':e.pageX,'clientY':e.pageY}];
    switch(true) {
    case (e.touches[0].clientY<window.innerHeight/3) : 
        position = 'top';
        break;
    case (e.touches[0].clientY>(2*window.innerHeight)/3) : 
        position = 'bottom';
        break;
    default : 
        position = 'middle';
        break;
    }
    position+='-';
    switch(true) {
    case (e.touches[0].clientX<window.innerWidth/3) : 
        position += 'left';
        break;
    case (e.touches[0].clientX>(2*window.innerWidth)/3) : 
        position += 'right';
        break;
    default : 
        position += 'center';
        break;  
    }

    if (!(position in areas)) {
      return true;
    }

    areas[position]();
    if (repeat!==0) {
      clearInterval(touchtimer);
      touchtimer= setInterval(areas[position], repeat);
    }
    return false;
  };
  // Cancel timeout
  document.onmouseup = document.ontouchend= function(e) {
  clearInterval(touchtimer);
  };
};

Now, all you need to do to attach a function to a touch event in the top-left area of the screen is:

TouchController({
  'top-left': function() { topLeftFunction();}
}, 20);

I use this for direction control in the Mario Kart experiment which maps exactly onto the cursor keys used for the normal control.

TouchController({
  'top-left': function() {  // UP + LEFT
				drawMap.move({y: 2}); 
				drawMap.move({z: drawMap.z + 2}); 
				drawMap.sprite(-1) 
			  },
  'top-center': function() {  // UP
				drawMap.move({y: 2}); 
			  },
  'top-right': function() {  // UP + RIGHT
				drawMap.move({y: 2}); 
				drawMap.move({z: drawMap.z - 2}); 
				drawMap.sprite(1) 
			  },

  'middle-left': function() {  // LEFT
				drawMap.move({z: drawMap.z + 2}); 
				drawMap.sprite(-1) 
			  },
  'middle-right': function() {  // RIGHT
				drawMap.move({z: drawMap.z - 2});
				drawMap.sprite(1) 
			  },

  'bottom-left': function() {  // DOWN + LEFT
				drawMap.move({y:  - 2}); 
				drawMap.move({z: drawMap.z + 2}); 
				drawMap.sprite(-1)  
			  },
  'bottom-center': function() { 
				drawMap.move({y:  - 2}); 
			  },
  'bottom-right': function() {  // DOWN + RIGHT
				drawMap.move({y:  - 2}); 
				drawMap.move({z: drawMap.z - 2}); 
				drawMap.sprite(1)  
			  },
}, 20);

If you need anything clever or you need two or more touches, you should use something else. This is just a simple drop-in for when you're copy-paste coding and want to include touch-screen support.