A Pen by Ulric Wilfred on CodePen.
Last active
August 31, 2017 17:09
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A Star Warp with Canvas
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<canvas width="1400" height="1000"> | |
</canvas> | |
<button>Restart</button> |
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const WIDTH = 1400; | |
const HEIGHT = 1000; | |
const STARS_COUNT = 100; | |
const STAR_MAX_RADIUS = 5; | |
const START_AT = 500; // in ms | |
const ANIMATION_DURATION = 2000; // in ms | |
const FADE_DURATION = 4000; // in ms | |
const TRAVEL_LENGTH = 200; // in px | |
const cvs = document.getElementsByTagName('canvas')[0]; | |
const ctx = cvs.getContext('2d'); | |
const pxRatio = window.devicePixelRatio || 1; | |
//ctx.scale(pxRatio, pxRatio); | |
const vectorLength = (x1, y1, x2, y2) => Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); | |
const createStars = () => | |
Array.from( | |
new Array(STARS_COUNT), | |
() => { | |
const x = Math.random() * WIDTH, | |
y = Math.random() * HEIGHT, | |
radius = Math.random() * STAR_MAX_RADIUS, | |
circRadius = vectorLength(x, y, WIDTH / 2, HEIGHT / 2), | |
angle = Math.atan2(y - HEIGHT / 2, x - WIDTH / 2); | |
return { x, y, radius, circRadius, angle }; | |
} | |
); | |
let stars = createStars(); | |
let startTime = new Date().getTime(); | |
let lastTime = startTime, dt; | |
let animationPos; | |
const restartButton = document.getElementsByTagName('button')[0]; | |
restartButton.addEventListener('click', () => { | |
stars = createStars(); | |
startTime = new Date().getTime(); | |
lastTime = startTime; | |
}); | |
const animate = () => { | |
dt = new Date().getTime() - lastTime; | |
lastTime += dt; | |
animationPos = (lastTime - startTime - START_AT) / ANIMATION_DURATION; | |
ctx.fillStyle = 'midnightblue'; | |
ctx.fillRect(0, 0, WIDTH, HEIGHT); | |
for (const star of stars) { | |
if (animationPos < 0) { | |
ctx.fillStyle = 'white'; | |
ctx.beginPath(); | |
ctx.arc(star.x, star.y, star.radius, 0, 2 * Math.PI, false); | |
ctx.fill(); | |
// ctx.lineWidth = 1; | |
// ctx.strokeStyle = 'rgba(255, 255, 255, 0.3)'; | |
// ctx.beginPath(); | |
// ctx.arc(WIDTH / 2, HEIGHT / 2, star.circRadius, 0, 2 * Math.PI, false); | |
// ctx.stroke(); | |
} | |
if ((animationPos >= 0) && (animationPos <= 1)) { | |
const nextCircRadius = star.circRadius + (animationPos * TRAVEL_LENGTH); | |
const newX = WIDTH / 2 + nextCircRadius * Math.cos(star.angle); | |
const newY = HEIGHT / 2 + nextCircRadius * Math.sin(star.angle); | |
ctx.strokeStyle = 'white'; | |
ctx.fillStyle = 'white'; | |
ctx.lineWidth = star.radius * 1.5; | |
ctx.beginPath(); | |
ctx.moveTo(star.x, star.y); | |
ctx.lineTo(newX, newY); | |
ctx.closePath(); | |
ctx.stroke(); | |
ctx.arc(newX, newY, star.radius, 0, 2 * Math.PI, false); | |
ctx.fill(); | |
// ctx.strokeStyle = 'rgba(255, 255, 255, 0.3)'; | |
// ctx.beginPath(); | |
// ctx.arc(WIDTH / 2, HEIGHT / 2, star.circRadius + (animationPos * TRAVEL_LENGTH), 0, 2 * Math.PI, false); | |
// ctx.stroke(); | |
} | |
if ((animationPos > 1)/* && ((animationPos - 1.0) * ANIMATION_DURATION <= FADE_DURATION)*/) { | |
const opacity = (animationPos - 1.0) * ANIMATION_DURATION / FADE_DURATION; | |
if (opacity <= 1) { | |
ctx.fillStyle = 'rgba(255, 255, 255, ' + (opacity < 1 ? 1.0 - opacity : 0) + ')'; | |
const nextCircRadius = star.circRadius + (animationPos * TRAVEL_LENGTH); | |
const newX = WIDTH / 2 + nextCircRadius * Math.cos(star.angle); | |
const newY = HEIGHT / 2 + nextCircRadius * Math.sin(star.angle); | |
ctx.beginPath(); | |
ctx.arc(newX, newY, star.radius, 0, 2 * Math.PI, false); | |
ctx.fill(); | |
} | |
ctx.fillStyle = 'rgba(255, 255, 255, ' + (opacity < 1 ? opacity : 1) + ')'; | |
ctx.beginPath(); | |
ctx.arc(star.x, star.y, star.radius, 0, 2 * Math.PI, false); | |
ctx.fill(); | |
} | |
}; | |
requestAnimationFrame(animate); | |
}; | |
requestAnimationFrame(animate); | |
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canvas { | |
width: 700px; | |
height: 500px; | |
} | |
button { | |
position: absolute; | |
top: 10px; | |
left: 720px; | |
font-size: 20px; | |
} |
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