add custom Materials

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

@@ -1,6 +1,8 @@
 package eu.jonahbauer.raytracing;
 
+import eu.jonahbauer.raytracing.material.LambertianMaterial;
 import eu.jonahbauer.raytracing.render.Camera;
+import eu.jonahbauer.raytracing.render.Color;
 import eu.jonahbauer.raytracing.render.ImageFormat;
 import eu.jonahbauer.raytracing.scene.Scene;
 import eu.jonahbauer.raytracing.scene.Sphere;
@@ -11,8 +13,8 @@ import java.nio.file.Path;
 public class Main {
     public static void main(String[] args) throws IOException {
         var scene = new Scene(
-                new Sphere(0, 0, 1, 0.5),
-                new Sphere(0, -100.5, 1, 100)
+                new Sphere(0, 0, 1, 0.5, new LambertianMaterial(Color.RED)),
+                new Sphere(0, -100.5, 1, 100, new LambertianMaterial(Color.BLUE))
         );
         var camera = new Camera(512, 2, 16 / 9d);
 

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

@@ -0,0 +1,25 @@
+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;
+
+import java.util.Objects;
+import java.util.Optional;
+
+public record LambertianMaterial(@NotNull Color albedo) implements Material {
+    public LambertianMaterial {
+        Objects.requireNonNull(albedo, "albedo");
+    }
+
+    @Override
+    public @NotNull Optional<ScatterResult> scatter(@NotNull Ray ray, @NotNull HitResult hit) {
+        var newDirection = hit.normal().plus(Vec3.random(true));
+        if (newDirection.isNearZero()) newDirection = hit.normal();
+
+        var scattered = new Ray(hit.position(), newDirection);
+        return Optional.of(new ScatterResult(scattered, albedo));
+    }
+}

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

@@ -0,0 +1,21 @@
+package eu.jonahbauer.raytracing.material;
+
+import eu.jonahbauer.raytracing.math.Ray;
+import eu.jonahbauer.raytracing.render.Color;
+import eu.jonahbauer.raytracing.scene.HitResult;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Objects;
+import java.util.Optional;
+
+public interface Material {
+
+    @NotNull Optional<ScatterResult> scatter(@NotNull Ray ray, @NotNull HitResult hit);
+
+    record ScatterResult(@NotNull Ray ray, @NotNull Color attenuation) {
+        public ScatterResult {
+            Objects.requireNonNull(ray, "ray");
+            Objects.requireNonNull(attenuation, "attenuation");
+        }
+    }
+}

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

@@ -63,6 +63,11 @@ public record Vec3(double x, double y, double z) {
         return Math.sqrt(squared());
     }
 
+    public boolean isNearZero() {
+        var s = 1e-8;
+        return Math.abs(x) < s && Math.abs(y) < s && Math.abs(z) < s;
+    }
+    
     public @NotNull Vec3 unit() {
         return div(length());
     }

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

@@ -137,12 +137,11 @@ public final class Camera {
 
         var optional = scene.hit(ray, new Range(0.001, Double.POSITIVE_INFINITY));
         if (optional.isPresent()) {
-            var result = optional.get();
-
-            var newDirection = result.normal().plus(Vec3.random(true));
-            var scattered = new Ray(result.position(), newDirection);
-
-            return Color.lerp(Color.BLACK, getColor(scene, scattered, depth - 1), 0.5);
+            var hit = optional.get();
+            var material = hit.material();
+            return material.scatter(ray, hit)
+                    .map(scatter -> Color.multiply(scatter.attenuation(), getColor(scene, scatter.ray(), depth - 1)))
+                    .orElse(Color.BLACK);
         } else {
             return getSkyboxColor(ray);
         }

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

@@ -7,6 +7,8 @@ public record Color(double r, double g, double b) {
     public static final @NotNull Color WHITE = new Color(1.0, 1.0, 1.0);
     public static final @NotNull Color SKY = new Color(0.5, 0.7, 1.0);
     public static final @NotNull Color RED = new Color(1.0, 0.0, 0.0);
+    public static final @NotNull Color GREEN = new Color(0.0, 1.0, 0.0);
+    public static final @NotNull Color BLUE = new Color(0.0, 0.0, 1.0);
 
     public static @NotNull Color lerp(@NotNull Color a, @NotNull Color b, double t) {
         if (t < 0) return a;
@@ -18,6 +20,10 @@ public record Color(double r, double g, double b) {
         );
     }
 
+    public static @NotNull Color multiply(@NotNull Color a, @NotNull Color b) {
+        return new Color(a.r() * b.r(), a.g() * b.g(), a.b() * b.b());
+    }
+
     public Color {
         if (r < 0 || r > 1 || g < 0 || g > 1 || b < 0 || b > 1) {
             throw new IllegalArgumentException("r, g and b must be in the range 0 to 1");

src/main/java/eu/jonahbauer/raytracing/scene/HitResult.java

@@ -1,11 +1,17 @@
 package eu.jonahbauer.raytracing.scene;
 
 import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.material.Material;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Objects;
 
-public record HitResult(double t, @NotNull Vec3 position, @NotNull Vec3 normal) implements Comparable<HitResult> {
+public record HitResult(
+        double t,
+        @NotNull Vec3 position,
+        @NotNull Vec3 normal,
+        @NotNull Material material
+) implements Comparable<HitResult> {
     public HitResult {
         if (t < 0 || !Double.isFinite(t)) throw new IllegalArgumentException("t must be non-negative");
         Objects.requireNonNull(position, "position");

src/main/java/eu/jonahbauer/raytracing/scene/Sphere.java

@@ -1,5 +1,6 @@
 package eu.jonahbauer.raytracing.scene;
 
+import eu.jonahbauer.raytracing.material.Material;
 import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.math.Vec3;
@@ -8,16 +9,16 @@ import org.jetbrains.annotations.NotNull;
 import java.util.Objects;
 import java.util.Optional;
 
-public record Sphere(@NotNull Vec3 center, double radius) implements Hittable {
-    public static final @NotNull Sphere UNIT = new Sphere(Vec3.ZERO, 1.0);
+public record Sphere(@NotNull Vec3 center, double radius, @NotNull Material material) implements Hittable {
 
     public Sphere {
         Objects.requireNonNull(center, "center");
+        Objects.requireNonNull(material, "material");
         if (radius <= 0 || !Double.isFinite(radius)) throw new IllegalArgumentException("radius must be positive");
     }
 
-    public Sphere(double x, double y, double z, double r) {
-        this(new Vec3(x, y, z), r);
+    public Sphere(double x, double y, double z, double r, @NotNull Material material) {
+        this(new Vec3(x, y, z), r, material);
     }
 
     @Override
@@ -38,11 +39,11 @@ public record Sphere(@NotNull Vec3 center, double radius) implements Hittable {
         if (!range.surrounds(t)) return Optional.empty();
 
         var position = ray.at(t);
-        return Optional.of(new HitResult(t, position, position.minus(center)));
+        return Optional.of(new HitResult(t, position, position.minus(center), material));
     }
 
     public @NotNull Sphere withCenter(@NotNull Vec3 center) {
-        return new Sphere(center, radius);
+        return new Sphere(center, radius, material);
     }
 
     public @NotNull Sphere withCenter(double x, double y, double z) {
@@ -50,6 +51,6 @@ public record Sphere(@NotNull Vec3 center, double radius) implements Hittable {
     }
 
     public @NotNull Sphere withRadius(double radius) {
-        return new Sphere(center, radius);
+        return new Sphere(center, radius, material);
     }
 }