iwmlib/lib/imageloader.html

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2019-03-21 09:57:27 +01:00
<!doctype html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<link rel="stylesheet" href="../lib/3rdparty/highlight/styles/default.css">
<link rel="stylesheet" href="../css/doctest.css">
<script src="../lib/3rdparty/highlight/highlight.pack.js"></script>
<script src="../lib/3rdparty/all.js"></script>
<script src="all.js"></script>
</head>
<body onload="Doctest.run()" >
<h1>Image Loader Worker</h1>
<p>
The loading of multiple small images (e.g. loadimng tiles of a zoomable
map) is a time consuming task that leads to small but noticeable delays
in touch interaction if standard DOM events are used. With a worker we
can try to do most of the time consuming processing in the background.
</p>
<p>Let's look at an example of a image loader worker:</p>
<img id="img1" width="160" height="120" class="grayBorder interactive" src=""/>
<img id="img2" width="160" height="120" class="grayBorder interactive" src=""/>
<img id="img3" width="160" height="120" class="grayBorder interactive" src=""/>
<img id="img4" width="160" height="120" class="grayBorder interactive" src=""/>
<script class="doctest">
let urls = [
'http://i.imgur.com/JmvCQXd.jpg',
'http://i.imgur.com/L4ipvCE.jpg',
'http://i.imgur.com/fKDIYIP.jpg',
'http://i.imgur.com/4ad4bo5.jpg'
]
let imgs = [img1, img2, img3, img4]
let count = 0
let worker = new Worker("imageloader.js")
worker.onmessage = (event) => {
console.log("Loaded", event.data)
if (event.data.success) {
console.log("Loaded", event.data.url)
imgs[count].src = event.data.url
count += 1
}
}
worker.postMessage({command: "load", urls: urls})
worker.postMessage({command: "abort", urls: urls})
worker.postMessage({command: "load", urls: urls})
</script>
</body>