2019-03-21 09:57:27 +01:00
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<!doctype html>
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<html lang="en">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>Coordinates Doctest</title>
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2019-05-22 16:03:19 +02:00
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<link rel="stylesheet" href="./3rdparty/highlight/styles/default.css">
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2019-03-21 09:57:27 +01:00
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<link rel="stylesheet" href="../css/doctest.css">
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<script src="./3rdparty/highlight/highlight.pack.js"></script>
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<script src="./3rdparty/all.js"></script>
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2019-05-22 16:03:19 +02:00
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<script src="../dist/iwmlib.js"></script>
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2019-03-21 09:57:27 +01:00
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<script>
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function drawPolygons() {
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canvas.width = main.getBoundingClientRect().width
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let context = canvas.getContext('2d')
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context.clearRect(0, 0, canvas.width, canvas.height)
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let stage = scatterContainer.polygon
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stage.draw(context, { stroke: '#FF0000' })
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for (let scatter of scatterContainer.scatter.values()) {
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let polygon = scatter.polygon
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polygon.draw(context, { stroke: '#FF0000' })
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}
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}
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function animate(callback) {
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requestAnimationFrame((dt) => {
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drawPolygons()
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callback()
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animate(callback)
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})
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}
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</script>
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</head>
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<body onload="Doctest.run()">
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<h1>
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Coordinates
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</h1>
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<p>
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To position objects in defined spatial relationships presupposes a clear understanding of the involved coordinate systems.
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Unfortunately, several systems with several conventions are involved:
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<a href="https://javascript.info/coordinates">DOM & CSS</a>,
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<a href="https://www.sarasoueidan.com/blog/svg-coordinate-systems/SVG">SVG</a>,
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<a href="https://www.w3schools.com/graphics/canvas_coordinates.asp">Canvas</a>
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</p>
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<p>
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We need a common reference system to switch between these coordinate systems. As the uttermost context, the browser page
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coordinate system is the most natural one. A simple API was long missing but has now been established in most modern
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browsers with
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<a href="https://developer.mozilla.org/en-US/docs/Web/API/Window/convertPointFromNoteToPage">window.convertPointFromNoteToPage</a> and the inverse
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<a href="https://developer.mozilla.org/en-US/docs/Web/API/Window/convertPointFromPageToNode">window.convertPointFromPageToNode</a>.
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Although MDN Web Docs warns about their Non-standard nature the methods work in browsers targeted
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by the IWM Browser project. This doctest assures that this assumption can be tested.
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</p>
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<p>Let's look at a scatter object with a rotatable local coordinate system. We try to follow a point in this local coordinate
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system by showing a marker outside the scatter that follows the point.
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</p>
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<div id="main" class="grayBorder interactive" style="position: relative; width: 100%; height: 280px;">
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<!-- Note that we need to set draggable to false to avoid conflicts. The DOM elements
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must also be positioned absolutely. -->
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<img id="women" draggable="false" style="position: absolute;" src="examples/women.jpeg" />
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<canvas id="canvas" height="280" style="z-index: 100000; pointer-events: none; position: absolute; border: 1px solid red;">
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Canvas not supported.
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</canvas>
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</div>
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<script class="doctest">
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let dx = 44
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let app = new App()
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let scatterContainer = new DOMScatterContainer(main)
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let angle = 15
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let image = document.getElementById('women')
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// The DOMScatter needs initial width and height. Therefore we
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// define the scatter when the image size is known, i.e. after loading...
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image.onload = (e) => {
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let scatter = new DOMScatter(image, scatterContainer, {
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x: dx,
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y: 44,
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width: e.target.naturalWidth,
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height: e.target.naturalHeight,
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rotationDegrees: angle,
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throwVisibility: 88,
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minScale: 0.5,
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maxScale: 1.5
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})
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dx += 300
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angle = -angle
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}
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app.run()
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function followPoint() {
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let context = canvas.getContext('2d')
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let localPoint = { x: 100, y: 100 }
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let globalPoint = convertPointFromNodeToPage(image, localPoint.x, localPoint.y)
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let canvasPoint = convertPointFromPageToNode(canvas, globalPoint.x, globalPoint.y)
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context.strokeStyle = 'red'
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context.beginPath()
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context.arc(canvasPoint.x, canvasPoint.y, 12, 0, Math.PI * 2)
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context.stroke()
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}
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animate(followPoint)
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</script>
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</body>
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