Hiệu ứng Canvas

Demo

Đầu tiên chèn CSS:

canvas { position: absolute; top: 0; left: 0; }

Tiếp đến là đoạn code dán vào nơi hiển thị:

<canvas id=c></canvas>
<script>
var w = c.width = window.innerWidth,
h = c.height = window.innerHeight,
ctx = c.getContext('2d'),
opts = {
 len: 20,
 count: 50,
 baseTime: 10,
 addedTime: 10,
 dieChance: .05,
 spawnChance: 1,
 sparkChance: .1,
 sparkDist: 10,
 sparkSize: 2,
 color: 'hsl(hue,100%,light%)',
 baseLight: 50,
 addedLight: 10,
 shadowToTimePropMult: 6,
 baseLightInputMultiplier: .01,
 addedLightInputMultiplier: .02,
 cx: w / 2,
 cy: h / 2,
 repaintAlpha: .04,
 hueChange: .1
},
tick = 0,
lines = [],
dieX = w / 2 / opts.len,
dieY = h / 2 / opts.len,
baseRad = Math.PI * 2 / 6;
ctx.fillStyle = 'black';
ctx.fillRect(0, 0, w, h);
function loop() {
 window.requestAnimationFrame(loop); ++tick;
 ctx.globalCompositeOperation = 'source-over';
 ctx.shadowBlur = 0;
 ctx.fillStyle = 'rgba(0,0,0,alp)'.replace('alp', opts.repaintAlpha);
 ctx.fillRect(0, 0, w, h);
 ctx.globalCompositeOperation = 'lighter';
 if (lines.length < opts.count && Math.random() < opts.spawnChance) lines.push(new Line);
 lines.map(function(line) {
  line.step()
 })
}
function Line() {
 this.reset()
}
Line.prototype.reset = function() {
 this.x = 0;
 this.y = 0;
 this.addedX = 0;
 this.addedY = 0;
 this.rad = 0;
 this.lightInputMultiplier = opts.baseLightInputMultiplier + opts.addedLightInputMultiplier * Math.random();
 this.color = opts.color.replace('hue', tick * opts.hueChange);
 this.cumulativeTime = 0;
 this.beginPhase()
}
Line.prototype.beginPhase = function() {
 this.x += this.addedX;
 this.y += this.addedY;
 this.time = 0;
 this.targetTime = (opts.baseTime + opts.addedTime * Math.random()) | 0;
 this.rad += baseRad * (Math.random() < .5 ? 1 : -1);
 this.addedX = Math.cos(this.rad);
 this.addedY = Math.sin(this.rad);
 if (Math.random() < opts.dieChance || this.x > dieX || this.x < -dieX || this.y > dieY || this.y < -dieY) this.reset()
}
Line.prototype.step = function() {++this.time; ++this.cumulativeTime;
 if (this.time >= this.targetTime) this.beginPhase();
 var prop = this.time / this.targetTime,
 wave = Math.sin(prop * Math.PI / 2),
 x = this.addedX * wave,
 y = this.addedY * wave;
 ctx.shadowBlur = prop * opts.shadowToTimePropMult;
 ctx.fillStyle = ctx.shadowColor = this.color.replace('light', opts.baseLight + opts.addedLight * Math.sin(this.cumulativeTime * this.lightInputMultiplier));
 ctx.fillRect(opts.cx + (this.x + x) * opts.len, opts.cy + (this.y + y) * opts.len, 2, 2);
 if (Math.random() < opts.sparkChance) ctx.fillRect(opts.cx + (this.x + x) * opts.len + Math.random() * opts.sparkDist * (Math.random() < .5 ? 1 : -1) - opts.sparkSize / 2, opts.cy + (this.y + y) * opts.len + Math.random() * opts.sparkDist * (Math.random() < .5 ? 1 : -1) - opts.sparkSize / 2, opts.sparkSize, opts.sparkSize)
}
loop();
window.addEventListener('resize',
function() {
 w = c.width = window.innerWidth;
 h = c.height = window.innerHeight;
 ctx.fillStyle = 'black';
 ctx.fillRect(0, 0, w, h);
 opts.cx = w / 2;
 opts.cy = h / 2;
 dieX = w / 2 / opts.len;
 dieY = h / 2 / opts.len
});
</script>

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