1 files changed, 74 insertions, 0 deletions
diff --git a/src/http/static/trading-in-the-rain/RainCanvas.js b/src/http/static/trading-in-the-rain/RainCanvas.js
new file mode 100644
index 0000000..5396eb5
--- /dev/null
+++ b/src/http/static/trading-in-the-rain/RainCanvas.js
@@ -0,0 +1,74 @@
+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);
+}