How to detect finger count on pointer events in IE 11

Question

I have implemented pointer events for canvas object. I need to know how we can detect finger count for touch events. Here is a piece of my code:

canvasObj.addEventListener( 'pointerenter', mouseEnterCall, false );
canvasObj.addEventListener( 'pointerdown',  mouseDownCall,  false );
canvasObj.addEventListener( 'pointermove',  mouseMoveCall,  false );
canvasObj.addEventListener( 'pointerup',    mouseUpCall,    false );
canvasObj.addEventListener( 'pointerout',   mouseOutCall,   false );

Appreciate your help.

Answer 1

There's no built-in property that gives you the current number of fingers (active pointers) on the screen. But here's some simple code that would achieve this:

var pointerCount = 0; //Stores current number of "active pointers"
window.addEventListener("pointerdown", addPointer, true); 
window.addEventListener("pointerup", removePointer, true); 
window.addEventListener("pointercancel", removePointer, true);
function addPointer(e) { pointerCount++ } 
function removePointer(e) { pointerCount-- }

You can modify addPointer to only count touch pointers, if that's what you want:

function addPointer(e) { if (e.pointerType === "touch") pointerCount++ } 

Note that you'll need to modify this code somewhat if you want to also support IE10, which has an earlier (prefixed) version of the standard.