/
Using_Pointer_Events.html
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/
Using_Pointer_Events.html
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<!doctype html>
<html lang="en">
<!--
This application is documented in "Using Pointer Events":
<https://developer.mozilla.org/en-US/docs/Web/API/Pointer_events/Using_Pointer_Events>
The application is a port of the example in "Using Touch events":
<https://developer.mozilla.org/en-US/docs/Web/API/Touch_events>
This port uses Pointer Events instead of Touch Events.
-->
<head>
<link rel="stylesheet" type="text/css" href="https://developer.mozilla.org/en-US/docs/Template:CustomSampleCSS?raw=1" />
</head>
<body>
<canvas id="canvas" width="600" height="300" style="border:solid black 1px; touch-action:none">
Your browser does not support canvas element.
</canvas>
<br>
<button onclick="startup();">Initialize</button>
<br>
Log:
<pre id="log" style="border: 1px solid #ccc;"></pre>
<script type="text/javascript">
function startup() {
var el = document.getElementsByTagName("canvas")[0];
el.addEventListener("pointerdown", handleStart, false);
el.addEventListener("pointerup", handleEnd, false);
el.addEventListener("pointercancel", handleCancel, false);
el.addEventListener("pointermove", handleMove, false);
log("initialized.");
}
var ongoingTouches = new Array();
function handleStart(evt) {
log("pointerdown.");
var el = document.getElementsByTagName("canvas")[0];
var ctx = el.getContext("2d");
log("pointerdown: id = " + evt.pointerId);
ongoingTouches.push(copyTouch(evt));
var color = colorForTouch(evt);
ctx.beginPath();
ctx.arc(touches[i].pageX, touches[i].pageY, 4, 0, 2 * Math.PI, false); // a circle at the start
ctx.arc(evt.clientX, evt.clientY, 4, 0, 2 * Math.PI, false); // a circle at the start
ctx.fillStyle = color;
ctx.fill();
}
function handleMove(evt) {
var el = document.getElementsByTagName("canvas")[0];
var ctx = el.getContext("2d");
var color = colorForTouch(evt);
var idx = ongoingTouchIndexById(evt.pointerId);
log("continuing touch: idx = " + idx);
if (idx >= 0) {
ctx.beginPath();
log("ctx.moveTo(" + ongoingTouches[idx].pageX + ", " + ongoingTouches[idx].pageY + ");");
ctx.moveTo(ongoingTouches[idx].pageX, ongoingTouches[idx].pageY);
log("ctx.lineTo(" + evt.clientX + ", " + evt.clientY + ");");
ctx.lineTo(evt.clientX, evt.clientY);
ctx.lineWidth = 4;
ctx.strokeStyle = color;
ctx.stroke();
ongoingTouches.splice(idx, 1, copyTouch(evt)); // swap in the new touch record
log(".");
} else {
log("can't figure out which touch to continue: idx = " + idx);
}
}
function handleEnd(evt) {
log("pointerup");
var el = document.getElementsByTagName("canvas")[0];
var ctx = el.getContext("2d");
var color = colorForTouch(evt);
var idx = ongoingTouchIndexById(evt.pointerId);
if (idx >= 0) {
ctx.lineWidth = 4;
ctx.fillStyle = color;
ctx.beginPath();
ctx.moveTo(ongoingTouches[idx].pageX, ongoingTouches[idx].pageY);
ctx.lineTo(evt.clientX, evt.clientY);
ctx.fillRect(evt.clientX - 4, evt.clientY - 4, 8, 8); // and a square at the end
ongoingTouches.splice(idx, 1); // remove it; we're done
} else {
log("can't figure out which touch to end");
}
}
function handleCancel(evt) {
log("pointercancel: id = " + evt.pointerId);
var idx = ongoingTouchIndexById(evt.pointerId);
ongoingTouches.splice(idx, 1); // remove it; we're done
}
function colorForTouch(touch) {
var r = touch.pointerId % 16;
var g = Math.floor(touch.pointerId / 3) % 16;
var b = Math.floor(touch.pointerId / 7) % 16;
r = r.toString(16); // make it a hex digit
g = g.toString(16); // make it a hex digit
b = b.toString(16); // make it a hex digit
var color = "#" + r + g + b;
log("color for touch with identifier " + touch.pointerId + " = " + color);
return color;
}
function copyTouch(touch) {
return { identifier: touch.pointerId, pageX: touch.clientX, pageY: touch.clientY };
}
function ongoingTouchIndexById(idToFind) {
for (var i = 0; i < ongoingTouches.length; i++) {
var id = ongoingTouches[i].identifier;
if (id == idToFind) {
return i;
}
}
return -1; // not found
}
function log(msg) {
var p = document.getElementById('log');
p.innerHTML = msg + "\n" + p.innerHTML;
}
</script>
</body>
</html>