add metal fuzz

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

@@ -16,8 +16,8 @@ public class Main {
         var scene = new Scene(
                 new Sphere(0, -100.5, 1, 100, new LambertianMaterial(new Color(0.8, 0.8, 0.0))),
                 new Sphere(0, 0, 1.2, 0.5, new LambertianMaterial(new Color(0.1, 0.2, 0.5))),
-                new Sphere(-1, 0, 1, 0.5, new MetallicMaterial(new Color(0.8, 0.8, 0.8))),
-                new Sphere(1, 0, 1, 0.5, new MetallicMaterial(new Color(0.8, 0.6, 0.2)))
+                new Sphere(-1, 0, 1, 0.5, new MetallicMaterial(new Color(0.8, 0.8, 0.8), 0.3)),
+                new Sphere(1, 0, 1, 0.5, new MetallicMaterial(new Color(0.8, 0.6, 0.2), 1.0))
         );
         var camera = new Camera(512, 2, 16 / 9d);
 

src/main/java/eu/jonahbauer/raytracing/material/MetallicMaterial.java

@@ -1,6 +1,7 @@
 package eu.jonahbauer.raytracing.material;
 
 import eu.jonahbauer.raytracing.math.Ray;
+import eu.jonahbauer.raytracing.math.Vec3;
 import eu.jonahbauer.raytracing.render.Color;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
@@ -8,16 +9,23 @@ import org.jetbrains.annotations.NotNull;
 import java.util.Objects;
 import java.util.Optional;
 
-public record MetallicMaterial(@NotNull Color albedo) implements Material {
+public record MetallicMaterial(@NotNull Color albedo, double fuzz) implements Material {
+
+    public MetallicMaterial(@NotNull Color albedo) {
+        this(albedo, 0);
+    }
+
     public MetallicMaterial {
         Objects.requireNonNull(albedo, "albedo");
+        if (fuzz < 0 || !Double.isFinite(fuzz)) throw new IllegalArgumentException("fuzz must be non-negative");
     }
 
     @Override
     public @NotNull Optional<ScatterResult> scatter(@NotNull Ray ray, @NotNull HitResult hit) {
-        var direction = ray.direction();
-        var normal = hit.normal();
-        var newDirection = direction.minus(normal.times(2 * normal.times(direction)));
+        var newDirection = Vec3.reflect(ray.direction(), hit.normal());
+        if (fuzz > 0) {
+            newDirection = newDirection.unit().plus(Vec3.random(true).times(fuzz));
+        }
         return Optional.of(new ScatterResult(new Ray(hit.position(), newDirection), albedo));
     }
 }

src/main/java/eu/jonahbauer/raytracing/math/Vec3.java

@@ -27,6 +27,10 @@ public record Vec3(double x, double y, double z) {
         return unit ? random.unit() : random;
     }
 
+    public static @NotNull Vec3 reflect(@NotNull Vec3 vec, @NotNull Vec3 normal) {
+        return vec.minus(normal.times(2 * normal.times(vec)));
+    }
+
     public @NotNull Vec3 plus(@NotNull Vec3 b) {
         return new Vec3(this.x + b.x, this.y + b.y, this.z + b.z);
     }