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