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function RainCanvas(canvasDOM) {
this.canvas = canvasDOM;
this.ctx = this.canvas.getContext("2d");
this.drops = [];
this.tick = 0;
// drop: {x, y, intensity, color} (all in range [0, 1], except color which is
// an array [r,g,b])
this.newDrop = (newDrop) => {
if (!document.hasFocus()) return;
// scale intensity up a bit right off the bat. If the intensity was near 0
// the drop wouldn't actually show up at all.
newDrop.intensity = distribute(newDrop.intensity, 0, 1, 0.1, 1);
newDrop.tick = this.tick;
this.drops.push(newDrop);
};
// alpha isn't really alpha, it's used to determine line width, but it plays
// the same role.
this.drawDrop = (drop, alpha) => {
let cW = this.canvas.width, cH = this.canvas.height;
let minDim = Math.min(cW, cH);
let tickDiff = this.tick - drop.tick;
let radius = tickDiff * (minDim / 250);
let x = distribute(drop.x, 0, 1, cW*0.1, cW*0.9);
let y = distribute(drop.y, 0, 1, cH*0.1, cH*0.9);
this.ctx.beginPath();
this.ctx.arc(x, y, radius, 0, Math.PI * 2, false);
this.ctx.closePath();
// multiple lineWidth by alpha so that the line width drops over time in
// correspondence with the opacity.
this.ctx.lineWidth = distribute(drop.intensity, 0, 1, 2, 9) * alpha;
let r = drop.color[0], g = drop.color[1], b = drop.color[2];
this.ctx.strokeStyle = `rgba(${r}, ${g}, ${b}, 1)`;
this.ctx.stroke();
};
let requestAnimationFrame =
window.requestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.msRequestAnimationFrame;
this.doTick = () => {
this.canvas.width = window.innerWidth;
this.canvas.height = window.innerHeight;
this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
let newDrops = [];
for (let i in this.drops) {
let drop = this.drops[i];
let alpha = distribute(
this.tick - drop.tick,
0, 200 * drop.intensity,
1, 0,
);
if (alpha <= 0) continue;
this.drawDrop(drop, alpha);
newDrops.push(drop);
}
this.drops = newDrops;
this.tick++;
requestAnimationFrame(this.doTick);
};
requestAnimationFrame(this.doTick);
}
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