How to draw on a HTML5 canvas with a stylus

问题

I used onmousedown, onmousemove and onmouseup events to draw with JavaScript on a HTML5 canvas object. Everything is working.

Now I want to replace the mouse with a sylus (Wacom Intous Pro) Therefore I replaced the mouse Events with onpointerdown, onpointerup and onpointermove.

But now, if I touch and move the pen, I do not get any onpointermove Events, instead the whole page is draged. By adding html, body {overflow: hidden} to the HTML construct I could Prevent this behaviour, but still I do not get any onpointermove Events. These I only get when the pen is above the tablet.

Has somebody an idea how to solve it?

Corrently this is the concept I use (but not working):

$(function() {
   var el=document.getElementById("myDraw");
    el.onpointerdown = down_handler;
    el.onpointerup = up_handler;
    el.onpointermove = move_handler;
    ctx = el.getContext("2d");
    ctx.canvas.width  = window.innerWidth*0.75;
    ctx.canvas.height = window.innerHeight*0.75;
});



function move_handler(ev) 
{ 
if (onTrack>0)
{
    var xPosition = ev.clientX-getPosition(document.getElementById("myDraw")).x;
    var yPosition = ev.clientY-getPosition(document.getElementById("myDraw")).y;
    ctx.beginPath();
    ctx.lineWidth=10*ev.pressure;
    ctx.moveTo(lastX,lastY);
    ctx.lineTo(xPosition,yPosition);
    ctx.stroke();     
    lastX = xPosition; 
    lastY = yPosition;
}
}

function down_handler(ev) 
{
    var xPosition = ev.clientX-getPosition(document.getElementById("myDraw")).x;
    var yPosition = ev.clientY-getPosition(document.getElementById("myDraw")).y;
    ctx.beginPath();
    ctx.arc(xPosition, yPosition, 5, 0, 2 * Math.PI);
    ctx.stroke();     
    startX = xPosition;
    startY = yPosition;
    lastX = xPosition;
    lastY = yPosition;
    onTrack=1;
    var el=document.getElementById("myRemoteDraw");
   el.setPointerCapture(ev.pointerId);
    console.log('pointer down '+ev.pointerId);
}


function up_handler(ev) 
{
    var xPosition = ev.clientX-getPosition(document.getElementById("myDraw")).x;
    var yPosition = ev.clientY-getPosition(document.getElementById("myDraw")).y;
    ctx.beginPath();
    ctx.rect(xPosition-5, yPosition-5, 10, 10);
    ctx.stroke();     
    onTrack = 0;
    var el=document.getElementById("myRemoteDraw");
    el.releasePointerCapture(ev.pointerId);
    console.log('pointer up '+ev.pointerId);
}

回答1:

This CSS should help you:

<style>
    /* Disable intrinsic user agent touch behaviors (such as panning or zooming) */
    canvas {
      touch-action: none;
    }
</style>

or in JavaScript:

ctx.canvas.style.touchAction = "none";

More details from this link about "touch-action" and some general info in this link about inputs:

The touch-action CSS property is used to specify whether or not the browser should apply its default (native) touch behavior (such as zooming or panning) to a region. This property may be applied to all elements except: non-replaced inline elements, table rows, row groups, table columns, and column groups.

A value of auto means the browser is free to apply its default touch behavior (to the specified region) and the value of none disables the browser's default touch behavior for the region. The values pan-x and pan-y, mean that touches that begin on the specified region are only for horizontal and vertical scrolling, respectively. The value manipulation means the browser may consider touches that begin on the element are only for scrolling and zooming.

来源：https://stackoverflow.com/questions/51581625/how-to-draw-on-a-html5-canvas-with-a-stylus

标签

javascript

html

stylus-pen