Folder structure

src/sky.js

@@ -0,0 +1,23 @@
+import {createCanvas, drawRect, clipCanvas, plot} from './gfx.js';
+import {randomInt, gradient} from './math.js';
+import {SKY_COLORS} from './constants.js';
+import {sample} from './utils.js';
+
+export function createSky(width, height) {
+  const ctx = createCanvas(width, height);
+  generateSky(ctx);
+  return ctx;
+}
+
+export function generateSky(ctx) {
+  const {width, height} = ctx.canvas;
+  const {from, to} = sample(SKY_COLORS);
+
+  for (let y=0; y<height; y++) {
+    const f = y / height;
+    const r = gradient(from[0], to[0], f);
+    const g = gradient(from[1], to[1], f);
+    const b = gradient(from[2], to[2], f);
+    drawRect(ctx, 0, y, width, 1, `rgb(${r},${g},${b})`);
+  }
+}