Improve rain scene

src/scenes/rain/rain-scene.ts

@@ -9,11 +9,9 @@ const WIND_SLANT = 0.2;
 
 export class RainScene implements Scene {
   private droplets: Array<DropletWrapper> = [];
-  private lights = [
-    new CircleLight(vec2.create(), rgb255(184, 41, 255), 1.5),
-    new CircleLight(vec2.create(), rgb255(255, 31, 109), 1.5),
-    new CircleLight(vec2.create(), rgb255(64, 110, 255), 1.5),
-  ];
+  // The moon: a single pale, cold light hanging high in the sky and the scene's
+  // only light source — the falling rain only shows where its streaks catch it.
+  private moon = new CircleLight(vec2.create(), rgb255(200, 214, 255), 2.5);
 
   private overlay: HTMLDivElement;
   public insights?: any;
@@ -41,14 +39,18 @@ export class RainScene implements Scene {
         },
         {
           ...CircleLight.descriptor,
-          shaderCombinationSteps: [0, 3],
+          shaderCombinationSteps: [0, 1],
         },
       ],
       this.drawNextFrame.bind(this),
       {
-        backgroundColor: rgb(0.5, 0.5, 0.5),
-        ambientLight: rgb(0.2, 0.2, 0.23),
+        // A dark night sky so the moon is the dominant light.
+        backgroundColor: rgb(0.09, 0.12, 0.19),
+        ambientLight: rgb(0.2, 0.22, 0.28),
         enableHighDpiRendering: true,
+        // Keep most of the previous frame each render so the droplets smear
+        // into long streaks of rain.
+        motionBlur: 0.9,
         // More, smaller tiles keep the droplet count per tile low.
         tileMultiplier: 12,
       }
@@ -70,19 +72,17 @@ export class RainScene implements Scene {
 
     const viewAreaSize = renderer.viewAreaSize;
 
-    // each light sweeps within its own third of the screen
-    this.lights.forEach((light, i) => {
+    // The moon drifts back and forth along the top edge; the rain falls past
+    // it and lights up.
     vec2.set(
-        light.center,
-        viewAreaSize.x *
-          ((i + 0.5) / 3 + (1 / 6) * Math.sin(currentTime / 900 + (i * Math.PI * 2) / 3)),
-        0
+      this.moon.center,
+      viewAreaSize.x * (0.5 + 0.5 * Math.sin(currentTime / 2500)),
+      viewAreaSize.y * 0.95
     );
-    });
 
     this.droplets.forEach((d) => d.animate(currentTime, viewAreaSize, WIND_SLANT));
 
-    [...this.droplets.map((d) => d.drawable), ...this.lights].forEach((d) =>
+    [...this.droplets.map((d) => d.drawable), this.moon].forEach((d) =>
       renderer.addDrawable(d)
     );