switch from octree to binary tree

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

@@ -3,6 +3,7 @@ package eu.jonahbauer.raytracing.math;
 import eu.jonahbauer.raytracing.scene.Hittable;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.Comparator;
 import java.util.List;
 import java.util.Optional;
 
@@ -12,6 +13,9 @@ import java.util.Optional;
 public record AABB(@NotNull Vec3 min, @NotNull Vec3 max) {
     public static final AABB UNIVERSE = new AABB(Vec3.MIN, Vec3.MAX);
     public static final AABB EMPTY = new AABB(Vec3.ZERO, Vec3.ZERO);
+    public static final Comparator<AABB> X_AXIS = Comparator.comparing(AABB::min, Comparator.comparingDouble(Vec3::x));
+    public static final Comparator<AABB> Y_AXIS = Comparator.comparing(AABB::min, Comparator.comparingDouble(Vec3::y));
+    public static final Comparator<AABB> Z_AXIS = Comparator.comparing(AABB::min, Comparator.comparingDouble(Vec3::z));
 
     public AABB {
         var a = min;
@@ -58,13 +62,17 @@ public record AABB(@NotNull Vec3 min, @NotNull Vec3 max) {
 
     public @NotNull Optional<Range> intersect(@NotNull Ray ray) {
         if (this == UNIVERSE) return Optional.of(Range.UNIVERSE);
+        if (this == EMPTY) return Optional.empty();
 
         int vmask = ray.vmask();
 
+        var origin = ray.origin();
+        var invDirection = ray.direction().inv();
+
         // calculate t values for intersection points of ray with planes through min
-        var tmin = intersect(min(), ray);
+        var tmin = intersect(min(), origin, invDirection);
         // calculate t values for intersection points of ray with planes through max
-        var tmax = intersect(max(), ray);
+        var tmax = intersect(max(), origin, invDirection);
 
         // determine range of t for which the ray is inside this voxel
         double tlmax = Double.NEGATIVE_INFINITY; // lower limit maximum
@@ -86,10 +94,14 @@ public record AABB(@NotNull Vec3 min, @NotNull Vec3 max) {
     }
 
     public static double @NotNull[] intersect(@NotNull Vec3 corner, @NotNull Ray ray) {
+        return intersect(corner, ray.origin(), ray.direction().inv());
+    }
+
+    private static double @NotNull[] intersect(@NotNull Vec3 corner, @NotNull Vec3 origin, @NotNull Vec3 invDirection) {
         return new double[] {
-                (corner.x() - ray.origin().x()) / ray.direction().x(),
-                (corner.y() - ray.origin().y()) / ray.direction().y(),
-                (corner.z() - ray.origin().z()) / ray.direction().z(),
+                (corner.x() - origin.x()) * invDirection.x(),
+                (corner.y() - origin.y()) * invDirection.y(),
+                (corner.z() - origin.z()) * invDirection.z(),
         };
     }
 }

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

@@ -16,4 +16,8 @@ public record Range(double min, double max) {
     public boolean surrounds(double value) {
         return min < value && value < max;
     }
+
+    public double size() {
+        return max - min;
+    }
 }

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

@@ -106,6 +106,10 @@ public record Vec3(double x, double y, double z) {
         return new Vec3(-x, -y, -z);
     }
 
+    public @NotNull Vec3 inv() {
+        return new Vec3(1 / x, 1 / y, 1 / z);
+    }
+
     public @NotNull Vec3 cross(@NotNull Vec3 b) {
         return new Vec3(
                 this.y() * b.z() - b.y() * this.z(),

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

@@ -3,17 +3,15 @@ package eu.jonahbauer.raytracing.scene;
 import eu.jonahbauer.raytracing.math.AABB;
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.render.Color;
+import eu.jonahbauer.raytracing.scene.util.HittableBinaryTree;
 import eu.jonahbauer.raytracing.scene.util.HittableCollection;
-import eu.jonahbauer.raytracing.scene.util.HittableList;
-import eu.jonahbauer.raytracing.scene.util.HittableOctree;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.ArrayList;
 import java.util.List;
+import java.util.Objects;
 
 public final class Scene extends HittableCollection {
-    private final @NotNull HittableOctree octree;
-    private final @NotNull HittableList list;
+    private final @NotNull HittableCollection objects;
     private final @NotNull SkyBox background;
 
     public Scene(@NotNull List<? extends @NotNull Hittable> objects) {
@@ -25,20 +23,8 @@ public final class Scene extends HittableCollection {
     }
 
     public Scene(@NotNull SkyBox background, @NotNull List<? extends @NotNull Hittable> objects) {
-        var bounded = new ArrayList<Hittable>();
-        var unbounded = new ArrayList<Hittable>();
-
-        objects.forEach(object -> {
-            if (object.getBoundingBox().isPresent()) {
-                bounded.add(object);
-            } else {
-                unbounded.add(object);
-            }
-        });
-
-        this.octree = new HittableOctree(bounded);
-        this.list = new HittableList(unbounded);
-        this.background = background;
+        this.objects = new HittableBinaryTree(objects);
+        this.background = Objects.requireNonNull(background);
     }
 
     public Scene(@NotNull Hittable @NotNull... objects) {
@@ -55,8 +41,7 @@ public final class Scene extends HittableCollection {
 
     @Override
     public void hit(@NotNull Ray ray, @NotNull State state) {
-        octree.hit(ray, state);
-        list.hit(ray, state);
+        objects.hit(ray, state);
     }
 
     @Override

src/main/java/eu/jonahbauer/raytracing/scene/util/HittableBinaryTree.java

@@ -0,0 +1,67 @@
+package eu.jonahbauer.raytracing.scene.util;
+
+import eu.jonahbauer.raytracing.math.AABB;
+import eu.jonahbauer.raytracing.math.Ray;
+import eu.jonahbauer.raytracing.scene.Hittable;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Comparator;
+import java.util.List;
+
+public final class HittableBinaryTree extends HittableCollection {
+    private final @Nullable Hittable left;
+    private final @Nullable Hittable right;
+    private final @NotNull AABB bbox;
+
+    public HittableBinaryTree(@NotNull List<? extends @NotNull Hittable> objects) {
+        bbox = AABB.getBoundingBox(objects).orElse(AABB.EMPTY);
+        if (objects.isEmpty()) {
+            left = null;
+            right = null;
+        } else if (objects.size() == 1) {
+            left = objects.getFirst();
+            right = null;
+        } else if (objects.size() == 2) {
+            left = objects.getFirst();
+            right = objects.getLast();
+        } else {
+            var x = bbox.x().size();
+            var y = bbox.y().size();
+            var z = bbox.z().size();
+            Comparator<AABB> comparator;
+            if (x > y && x > z) {
+                comparator = AABB.X_AXIS;
+            } else if (y > z) {
+                comparator = AABB.Y_AXIS;
+            } else {
+                comparator = AABB.Z_AXIS;
+            }
+            var sorted = objects.stream().sorted(Comparator.comparing(Hittable::getBoundingBox, comparator)).toList();
+            var size = sorted.size();
+
+            left = new HittableBinaryTree(sorted.subList(0, size / 2));
+            right = new HittableBinaryTree(sorted.subList(size / 2, size));
+        }
+    }
+
+    @Override
+    public void hit(@NotNull Ray ray, @NotNull State state) {
+        if (!bbox.hit(ray)) return;
+        if (left instanceof HittableCollection coll) {
+            coll.hit(ray, state);
+        } else if (left != null) {
+            hit(state, ray, left);
+        }
+        if (right instanceof HittableCollection coll) {
+            coll.hit(ray, state);
+        } else if (right != null) {
+            hit(state, ray, right);
+        }
+    }
+
+    @Override
+    public @NotNull AABB getBoundingBox() {
+        return bbox;
+    }
+}