add Range to optimize Shape#hit

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

@@ -0,0 +1,19 @@
+package eu.jonahbauer.raytracing.math;
+
+public record Range(double min, double max) {
+    public static final Range EMPTY = new Range(Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY);
+    public static final Range UNIVERSE = new Range(Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
+    public static final Range NON_NEGATIVE = new Range(0, Double.POSITIVE_INFINITY);
+
+    public Range {
+        if (Double.isNaN(min) || Double.isNaN(max)) throw new IllegalArgumentException("min and max must not be NaN");
+    }
+
+    public boolean contains(double value) {
+        return min <= value && value <= max;
+    }
+
+    public boolean surrounds(double value) {
+        return min < value && value < max;
+    }
+}

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

@@ -1,10 +1,12 @@
 package eu.jonahbauer.raytracing.render;
 
+import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
+import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.shape.HitResult;
 import eu.jonahbauer.raytracing.shape.Shape;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.Comparator;
 import java.util.List;
 import java.util.Optional;
 
@@ -26,18 +28,10 @@ public record Scene(@NotNull List<@NotNull Shape> shapes) {
             var y = pixel.y();
             var ray = pixel.ray();
 
-            var result = shapes.stream()
-                    .map(shape -> shape.hit(ray))
-                    .flatMap(Optional::stream)
-                    .min(Comparator.naturalOrder());
-
+            var result = hit(ray);
             if (result.isPresent()) {
                 var normal = result.get().normal();
-                image.set(x, y, new Color(
-                        0.5 * (normal.x() + 1),
-                        0.5 * (normal.y() + 1),
-                        0.5 * (normal.z() + 1)
-                ));
+                image.set(x, y, getNormalColor(normal));
             } else {
                 image.set(x, y, getSkyboxColor(ray));
             }
@@ -46,6 +40,27 @@ public record Scene(@NotNull List<@NotNull Shape> shapes) {
         return image;
     }
 
+    private @NotNull Optional<HitResult> hit(@NotNull Ray ray) {
+        var range = new Range(0, Double.POSITIVE_INFINITY);
+        var result = (HitResult) null;
+        for (var shape : shapes) {
+            var r = shape.hit(ray, range);
+            if (r.isPresent() && (result == null || r.get().t() < result.t())) {
+                result = r.get();
+                range = new Range(0, result.t());
+            }
+        }
+        return Optional.ofNullable(result);
+    }
+
+    private @NotNull Color getNormalColor(@NotNull Vec3 normal) {
+        return new Color(
+                0.5 * (normal.x() + 1),
+                0.5 * (normal.y() + 1),
+                0.5 * (normal.z() + 1)
+        );
+    }
+
     private @NotNull Color getSkyboxColor(@NotNull Ray ray) {
         // altitude from -pi/2 to pi/2
         var alt = Math.copySign(

src/main/java/eu/jonahbauer/raytracing/shape/Shape.java

@@ -1,5 +1,6 @@
 package eu.jonahbauer.raytracing.shape;
 
+import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
 import org.jetbrains.annotations.NotNull;
 
@@ -12,5 +13,5 @@ public sealed interface Shape permits Sphere {
      * the ray origin, or <code>Double.NaN</code> if the ray does not intersect this shape}
      * @param ray a ray
      */
-    @NotNull Optional<HitResult> hit(@NotNull Ray ray);
+    @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range);
 }

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

@@ -1,5 +1,6 @@
 package eu.jonahbauer.raytracing.shape;
 
+import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.math.Vec3;
 import org.jetbrains.annotations.NotNull;
@@ -20,7 +21,7 @@ public record Sphere(@NotNull Vec3 center, double radius) implements Shape {
     }
 
     @Override
-    public @NotNull Optional<HitResult> hit(@NotNull Ray ray) {
+    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
         var oc = ray.origin().minus(center());
 
         var a = ray.direction().squared();
@@ -33,8 +34,8 @@ public record Sphere(@NotNull Vec3 center, double radius) implements Shape {
         var sd = Math.sqrt(discriminant);
 
         double t = (- h - sd) / a;
-        if (t < 0) t = (- h + sd) / a;
-        if (t < 0) return Optional.empty();
+        if (!range.surrounds(t)) t = (- h + sd) / a;
+        if (!range.surrounds(t)) return Optional.empty();
         return Optional.of(new HitResult(t, ray.at(t).minus(center)));
     }
 

src/test/java/eu/jonahbauer/raytracing/shape/SphereTest.java

@@ -1,5 +1,6 @@
 package eu.jonahbauer.raytracing.shape;
 
+import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.math.Vec3;
 import org.junit.jupiter.api.Test;
@@ -18,7 +19,7 @@ class SphereTest {
         var direction = new Vec3(-1, -1, -1);
         var ray = new Ray(origin, direction);
 
-        var result = sphere.hit(ray);
+        var result = sphere.hit(ray, Range.NON_NEGATIVE);
         assertFalse(result.isEmpty());
         assertEquals(center.plus(new Vec3(1, 1, 1).unit().times(radius)), ray.at(result.get().t()));
     }