From 1d48a499873198fd319ed32cf8629eefd65eda32 Mon Sep 17 00:00:00 2001
From: jbb01 <32650546+jbb01@users.noreply.github.com>
Date: Wed, 7 Aug 2024 15:50:09 +0200
Subject: [PATCH] refactor AABB intersection

---
 .../eu/jonahbauer/raytracing/Examples.java    |  2 +-
 .../eu/jonahbauer/raytracing/math/AABB.java   | 36 ++++++++++---------
 .../eu/jonahbauer/raytracing/math/Vec3.java   |  9 +++++
 3 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/src/main/java/eu/jonahbauer/raytracing/Examples.java b/src/main/java/eu/jonahbauer/raytracing/Examples.java
index 5f38dcb..8e55352 100644
--- a/src/main/java/eu/jonahbauer/raytracing/Examples.java
+++ b/src/main/java/eu/jonahbauer/raytracing/Examples.java
@@ -316,7 +316,7 @@ public class Examples {
                 var x1 = x0 + w;
                 var y1 = random.nextInt(1, 101);
                 var z1 = z0 + w;
-                boxes.add(new Box(new Vec3(x0, y0, z0), new Vec3(x1, y1, z1), ground));
+                boxes.add(Hittables.box(new Vec3(x0, y0, z0), new Vec3(x1, y1, z1), ground));
             }
         }
         objects.add(new HittableBinaryTree(boxes));
diff --git a/src/main/java/eu/jonahbauer/raytracing/math/AABB.java b/src/main/java/eu/jonahbauer/raytracing/math/AABB.java
index 44796fc..b01dd28 100644
--- a/src/main/java/eu/jonahbauer/raytracing/math/AABB.java
+++ b/src/main/java/eu/jonahbauer/raytracing/math/AABB.java
@@ -2,6 +2,7 @@ package eu.jonahbauer.raytracing.math;
 
 import eu.jonahbauer.raytracing.scene.Hittable;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Comparator;
 import java.util.List;
@@ -11,7 +12,6 @@ import java.util.Optional;
  * An axis-aligned bounding box.
  */
 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));
@@ -57,17 +57,13 @@ public record AABB(@NotNull Vec3 min, @NotNull Vec3 max) {
     }
 
     public boolean hit(@NotNull Ray ray) {
-        return intersect(ray).isPresent();
+        return intersect(ray) != null;
     }
 
-    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();
-
+    public @Nullable Range intersect(@NotNull Ray ray) {
         var origin = ray.origin();
-        var invDirection = ray.direction().inv();
+        var direction = ray.direction();
+        var invDirection = direction.inv();
 
         // calculate t values for intersection points of ray with planes through min
         var tmin = intersect(min(), origin, invDirection);
@@ -78,19 +74,27 @@ public record AABB(@NotNull Vec3 min, @NotNull Vec3 max) {
         double tlmax = Double.NEGATIVE_INFINITY; // lower limit maximum
         double tumin = Double.POSITIVE_INFINITY; // upper limit minimum
         for (int i = 0; i < 3; i++) {
-            // classify t values as lower or upper limit based on vmask
-            if ((vmask & (1 << i)) == 0) {
+            // classify t values as lower or upper limit based on ray direction
+            if (direction.get(i) >= 0) {
                 // min is lower limit and max is upper limit
-                tlmax = Math.max(tlmax, tmin[i]);
-                tumin = Math.min(tumin, tmax[i]);
+                if (tmin[i] > tlmax) {
+                    tlmax = tmin[i];
+                }
+                if (tmax[i] < tumin) {
+                    tumin = tmax[i];
+                }
             } else {
                 // max is lower limit and min is upper limit
-                tlmax = Math.max(tlmax, tmax[i]);
-                tumin = Math.min(tumin, tmin[i]);
+                if (tmax[i] > tlmax) {
+                    tlmax = tmax[i];
+                }
+                if (tmin[i] < tumin) {
+                    tumin = tmin[i];
+                }
             }
         }
 
-        return tlmax < tumin ? Optional.of(new Range(tlmax, tumin)) : Optional.empty();
+        return tlmax < tumin ? new Range(tlmax, tumin) : null;
     }
 
     public static double @NotNull[] intersect(@NotNull Vec3 corner, @NotNull Ray ray) {
diff --git a/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java b/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java
index 767febe..9e59a0a 100644
--- a/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java
+++ b/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java
@@ -146,6 +146,15 @@ public record Vec3(double x, double y, double z) {
         return div(length());
     }
 
+    public double get(int axis) {
+        return switch (axis) {
+            case 0 -> x;
+            case 1 -> y;
+            case 2 -> z;
+            default -> throw new IndexOutOfBoundsException(axis);
+        };
+    }
+
     public @NotNull Vec3 withX(double x) {
         return new Vec3(x, y, z);
     }