Finish first demo scene

src/helper/random.ts

@@ -15,4 +15,8 @@ export abstract class Random {
     t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
     return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
   }
+
+  public static getRandomInRange(from: number, to: number): number {
+    return from + Random.getRandom() * (to - from);
+  }
 }