html - 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

没有内置属性可以为您提供屏幕上当前手指（活动指针）的数量。但这里有一些简单的代码可以实现这一点：

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-- }

您可以修改 addPointer 以仅计算触摸指针，如果这是您想要的：

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

请注意，如果您还想支持 IE10，则需要稍微修改此代码，IE10 具有该标准的较早（前缀）版本。