add constant density mediums

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

@@ -11,6 +11,7 @@ import eu.jonahbauer.raytracing.render.material.*;
 import eu.jonahbauer.raytracing.render.renderer.SimpleRenderer;
 import eu.jonahbauer.raytracing.scene.*;
 import eu.jonahbauer.raytracing.scene.hittable2d.Parallelogram;
+import eu.jonahbauer.raytracing.scene.hittable3d.ConstantMedium;
 import eu.jonahbauer.raytracing.scene.hittable3d.Sphere;
 import eu.jonahbauer.raytracing.scene.util.Hittables;
 import org.jetbrains.annotations.NotNull;
@@ -22,7 +23,7 @@ import java.util.Random;
 
 public class Main {
     public static void main(String[] args) throws IOException {
-        var example = getCornellBox();
+        var example = getCornellBoxSmoke();
         var scene = example.scene();
         var camera = example.camera();
 
@@ -150,6 +151,38 @@ public class Main {
         );
     }
 
+    private static @NotNull Example getCornellBoxSmoke() {
+        var red = new LambertianMaterial(new Color(.65, .05, .05));
+        var white = new LambertianMaterial(new Color(.73, .73, .73));
+        var green = new LambertianMaterial(new Color(.12, .45, .15));
+        var light = new DiffuseLight(new Color(7.0, 7.0, 7.0));
+
+        return new Example(
+                new Scene(
+                        new Parallelogram(new Vec3(555, 0, 0), new Vec3(0, 555, 0), new Vec3(0, 0, 555), green),
+                        new Parallelogram(new Vec3(0, 0, 0), new Vec3(0, 555, 0), new Vec3(0, 0, 555), red),
+                        new Parallelogram(new Vec3(113, 554, 127), new Vec3(330, 0, 0), new Vec3(0, 0, 305), light),
+                        new Parallelogram(new Vec3(0, 0, 0), new Vec3(555, 0 ,0), new Vec3(0, 0, 555), white),
+                        new Parallelogram(new Vec3(555, 555, 555), new Vec3(-555, 0 ,0), new Vec3(0, 0, -555), white),
+                        new Parallelogram(new Vec3(0, 0, 555), new Vec3(555, 0 ,0), new Vec3(0, 555, 0), white),
+                        new ConstantMedium(
+                                Hittables.box(new Vec3(0, 0, 0), new Vec3(165, 330, 165), white).rotateY(Math.toRadians(15)).translate(new Vec3(265, 0, 295)),
+                                0.01, new IsotropicMaterial(Color.BLACK)
+                        ),
+                        new ConstantMedium(
+                                Hittables.box(new Vec3(0, 0, 0), new Vec3(165, 165, 165), white).rotateY(Math.toRadians(-18)).translate(new Vec3(130, 0, 65)),
+                                0.01, new IsotropicMaterial(Color.WHITE)
+                        )
+                ),
+                SimpleCamera.builder()
+                        .withImage(600, 600)
+                        .withFieldOfView(Math.toRadians(40))
+                        .withPosition(new Vec3(278, 278, -800))
+                        .withTarget(new Vec3(278, 278, 0))
+                        .build()
+        );
+    }
+
     private static @NotNull Scene getSimpleScene() {
         return new Scene(
                 getSkyBox(),

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

@@ -11,7 +11,6 @@ public record Ray(@NotNull Vec3 origin, @NotNull Vec3 direction) {
     }
 
     public @NotNull Vec3 at(double t) {
-        if (t < 0) throw new IllegalArgumentException("t must not be negative");
         return new Vec3(
                 origin().x() + t * direction.x(),
                 origin().y() + t * direction.y(),

src/main/java/eu/jonahbauer/raytracing/render/material/IsotropicMaterial.java

@@ -0,0 +1,16 @@
+package eu.jonahbauer.raytracing.render.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.Optional;
+
+public record IsotropicMaterial(@NotNull Color albedo) implements Material{
+    @Override
+    public @NotNull Optional<ScatterResult> scatter(@NotNull Ray ray, @NotNull HitResult hit) {
+        return Optional.of(new ScatterResult(new Ray(hit.position(), Vec3.random(true)), albedo()));
+    }
+}

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

@@ -14,7 +14,6 @@ public record HitResult(
         boolean frontFace
 ) implements Comparable<HitResult> {
     public HitResult {
-        if (t < 0 || !Double.isFinite(t)) throw new IllegalArgumentException("t must be non-negative");
         Objects.requireNonNull(position, "position");
         normal = normal.unit();
     }

src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/ConstantMedium.java

@@ -0,0 +1,42 @@
+package eu.jonahbauer.raytracing.scene.hittable3d;
+
+import eu.jonahbauer.raytracing.math.BoundingBox;
+import eu.jonahbauer.raytracing.math.Range;
+import eu.jonahbauer.raytracing.math.Ray;
+import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.material.IsotropicMaterial;
+import eu.jonahbauer.raytracing.scene.HitResult;
+import eu.jonahbauer.raytracing.scene.Hittable;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Optional;
+
+public record ConstantMedium(@NotNull Hittable boundary, double density, @NotNull IsotropicMaterial material) implements Hittable {
+
+    @Override
+    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
+        var hit1 = boundary.hit(ray, Range.UNIVERSE);
+        if (hit1.isEmpty()) return Optional.empty();
+
+        var hit2 = boundary.hit(ray, new Range(hit1.get().t() + 0.0001, Double.POSITIVE_INFINITY));
+        if (hit2.isEmpty()) return Optional.empty();
+
+        var tmin = Math.max(range.min(), hit1.get().t());
+        var tmax = Math.min(range.max(), hit2.get().t());
+        if (tmin >= tmax) return Optional.empty();
+        if (tmin < 0) tmin = 0;
+
+        var length = ray.direction().length();
+        var distance = length * (tmax - tmin);
+        var hitDistance = - Math.log(Math.random()) / density;
+        if (hitDistance > distance) return Optional.empty();
+
+        var t = tmin + hitDistance / length;
+        return Optional.of(new HitResult(t, ray.at(t), Vec3.UNIT_X, material, true)); // arbitrary normal and frontFace
+    }
+
+    @Override
+    public @NotNull Optional<BoundingBox> getBoundingBox() {
+        return boundary().getBoundingBox();
+    }
+}