canvas粒子波

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// modified version of random-normal
function normalPool(o){var r=0;do{var a=Math.round(normal({mean:o.mean,dev:o.dev}));if(a<o.pool.length&&a>=0)return o.pool[a];r++}while(r<100)}function randomNormal(o){if(o=Object.assign({mean:0,dev:1,pool:[]},o),Array.isArray(o.pool)&&o.pool.length>0)return normalPool(o);var r,a,n,e,l=o.mean,t=o.dev;do{r=(a=2*Math.random()-1)*a+(n=2*Math.random()-1)*n}while(r>=1);return e=a*Math.sqrt(-2*Math.log(r)/r),t*e+l}

const NUM_PARTICLES = 100;
const PARTICLE_SIZE = 0.5; // View heights
const SPEED = 10000; // Milliseconds

let particles = [];

function rand(low, high) {
  return Math.random() * (high - low) + low;
}

function createParticle(canvas) {
  const colour = {
    r: 255,
    g: randomNormal({ mean: 125, dev: 20 }),
    b: 50,
    a: rand(0, 1),
  };
  return {
    x: -2,
    y: -2,
    diameter: Math.max(0, randomNormal({ mean: PARTICLE_SIZE, dev: PARTICLE_SIZE / 2 })),
    duration: randomNormal({ mean: SPEED, dev: SPEED * 0.1 }),
    amplitude: randomNormal({ mean: 16, dev: 2 }),
    offsetY: randomNormal({ mean: 0, dev: 10 }),
    arc: Math.PI * 2,
    startTime: performance.now() - rand(0, SPEED),
    colour: `rgba(${colour.r}, ${colour.g}, ${colour.b}, ${colour.a})`,
  }
}

function moveParticle(particle, canvas, time) {
  const progress = ((time - particle.startTime) % particle.duration) / particle.duration;
  return {
    ...particle,
    x: progress,
    y: ((Math.sin(progress * particle.arc) * particle.amplitude) + particle.offsetY),
  };
}

function drawParticle(particle, canvas, ctx) {
  canvas = document.getElementById('particle-canvas');
  const vh = canvas.height / 100;

ctx.fillStyle = particle.colour;
  ctx.beginPath();
  ctx.ellipse(
    particle.x * canvas.width,
    particle.y * vh + (canvas.height / 2),
    particle.diameter * vh,
    particle.diameter * vh,
    0,
    0,
    2 * Math.PI
  );
  ctx.fill();
}

function draw(time, canvas, ctx) {
  // Move particles
  particles.forEach((particle, index) => {
    particles[index] = moveParticle(particle, canvas, time);
  })

// Clear the canvas
  ctx.clearRect(0, 0, canvas.width, canvas.height);

// Draw the particles
  particles.forEach((particle) => {
    drawParticle(particle, canvas, ctx);
  })

// Schedule next frame
  requestAnimationFrame((time) => draw(time, canvas, ctx));
}

function initializeCanvas() {
  let canvas = document.getElementById('particle-canvas');
  canvas.width = canvas.offsetWidth * window.devicePixelRatio;
  canvas.height = canvas.offsetHeight * window.devicePixelRatio;
  let ctx = canvas.getContext("2d");

window.addEventListener('resize', () => {
    canvas.width = canvas.offsetWidth * window.devicePixelRatio;
    canvas.height = canvas.offsetHeight * window.devicePixelRatio;
    ctx = canvas.getContext("2d");
  })

return [canvas, ctx];
}

function startAnimation() {
  const [canvas, ctx] = initializeCanvas();

// Create a bunch of particles
  for (let i = 0; i < NUM_PARTICLES; i++) {
    particles.push(createParticle(canvas));
  }
  
  requestAnimationFrame((time) => draw(time, canvas, ctx));
};

// Start animation when document is loaded
(function () {
  if (document.readystate !== 'loading') {
    startAnimation();
  } else {
    document.addEventListener('DOMContentLoaded', () => {
      startAnimation();
    })
  }
}());

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