make scene deterministic

src/main/java/eu/jonahbauer/raytracing/Main.java

@@ -19,6 +19,7 @@ import org.jetbrains.annotations.NotNull;
 import java.io.IOException;
 import java.nio.file.Path;
 import java.util.ArrayList;
+import java.util.Random;
 
 public class Main {
     public static void main(String[] args) throws IOException {
@@ -47,24 +48,25 @@ public class Main {
     }
 
     private static @NotNull Scene getScene() {
+        var rng = new Random(1);
         var objects = new ArrayList<Hittable>();
         objects.add(new Sphere(new Vec3(0, -1000, 0), 1000, new LambertianMaterial(new Color(0.5, 0.5, 0.5))));
 
         for (int a = -11; a < 11; a++) {
             for (int b = -11; b < 11; b++) {
-                var center = new Vec3(a + 0.9 * Math.random(), 0.2, b + 0.9 * Math.random());
+                var center = new Vec3(a + 0.9 * rng.nextDouble(), 0.2, b + 0.9 * rng.nextDouble());
                 if (Vec3.distance(center, new Vec3(4, 0.2, 0)) <= 0.9) continue;
 
                 Material material;
-                var rnd = Math.random();
+                var rnd = rng.nextDouble();
                 if (rnd < 0.8) {
                     // diffuse
-                    var albedo = Color.multiply(Color.random(), Color.random());
+                    var albedo = Color.multiply(Color.random(rng), Color.random(rng));
                     material = new LambertianMaterial(albedo);
                 } else if (rnd < 0.95) {
                     // metal
-                    var albedo = Color.random(0.5, 1.0);
+                    var albedo = Color.random(rng, 0.5, 1.0);
-                    var fuzz = Math.random() * 0.5;
+                    var fuzz = rng.nextDouble() * 0.5;
                     material = new MetallicMaterial(albedo, fuzz);
                 } else {
                     // glass

src/main/java/eu/jonahbauer/raytracing/render/Color.java

@@ -2,6 +2,8 @@ package eu.jonahbauer.raytracing.render;
 
 import org.jetbrains.annotations.NotNull;
 
+import java.util.Random;
+
 public record Color(double r, double g, double b) {
     public static final @NotNull Color BLACK = new Color(0.0, 0.0, 0.0);
     public static final @NotNull Color WHITE = new Color(1.0, 1.0, 1.0);
@@ -24,16 +26,16 @@ public record Color(double r, double g, double b) {
         return new Color(a.r() * b.r(), a.g() * b.g(), a.b() * b.b());
     }
 
-    public static @NotNull Color random() {
+    public static @NotNull Color random(@NotNull Random random) {
-        return new Color(Math.random(), Math.random(), Math.random());
+        return new Color(random.nextDouble(), random.nextDouble(), random.nextDouble());
     }
 
-    public static @NotNull Color random(double min, double max) {
+    public static @NotNull Color random(@NotNull Random random, double min, double max) {
         var span = max - min;
         return new Color(
-                Math.fma(Math.random(), span, min),
+                Math.fma(random.nextDouble(), span, min),
-                Math.fma(Math.random(), span, min),
+                Math.fma(random.nextDouble(), span, min),
-                Math.fma(Math.random(), span, min)
+                Math.fma(random.nextDouble(), span, min)
         );
     }