mirror of https://github.com/nealey/vail.git
72 lines
1.5 KiB
HTML
72 lines
1.5 KiB
HTML
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<!DOCTYPE html>
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<html>
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<head>
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<title>Chart-O-Matic</title>
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<script>
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data = []
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const Millisecond = 1
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const Second = 1000 * Millisecond
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const ChartWidth = 20 * Second
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function draw(canvas) {
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let ctx = canvas.getContext("2d")
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let now = Date.now()
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let begin = now - ChartWidth
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let xScale = canvas.width / ChartWidth
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ctx.clearRect(0, 0, canvas.width, canvas.height)
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ctx.save()
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// Make 0,0 be the lower-left corner, like in PostScript
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ctx.scale(1, -1)
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ctx.translate(0, -canvas.height)
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ctx.strokeStyle = "red"
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ctx.lineWidth = 2
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let y = 0
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ctx.moveTo(0, y)
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ctx.beginPath()
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for (let point of data) {
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let x = (point[0] - begin) * xScale
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ctx.lineTo(x, y)
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y = point[1] * canvas.height
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ctx.lineTo(x, y)
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}
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ctx.stroke()
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ctx.restore()
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requestAnimationFrame(() => draw(canvas))
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}
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function update() {
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let now = Date.now()
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let earliest = now - ChartWidth
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data.push([now, Math.sin(now/Second)>0?1:0])
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while (data[0][0] < earliest) {
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data.shift()
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}
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}
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function init() {
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let canvas = document.querySelector("#chart")
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canvas.width = ChartWidth / (20 * Millisecond)
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setInterval(update, 50 * Millisecond)
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draw(canvas)
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}
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if (document.readyState === "loading") {
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document.addEventListener("DOMContentLoaded", init)
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} else {
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init()
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}
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</script>
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</head>
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<body>
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<h1>The Amazing Chart-O-Matic</h1>
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<canvas id="chart" style="border: solid black 1px; width: 100%;"></canvas>
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</body>
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</html>
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