3 files changed, 82 insertions, 0 deletions
diff --git a/src/Math/AABB.cpp b/src/Math/AABB.cpp
new file mode 100644
index 0000000..aa814a1
--- /dev/null
+++ b/src/Math/AABB.cpp
@@ -0,0 +1,17 @@
+// This file breaks the Ray.hpp <-> AABB.hpp dependency cycle.
+
+#include "AABB.hpp"
+#include "Ray.hpp"
+
+AABB AABB::cast_box(Vector<3> v, AABB against) const {
+    auto ray = Ray{center(), v};
+
+    auto expanded_target = against.sum(*this);
+    auto raycast = ray.cast(expanded_target);
+    if (!raycast.hit) return *this;
+
+    auto result_from = raycast.point - size() / 2.0;
+    auto result_to = result_from + size();
+
+    return {result_from, result_to};
+}
diff --git a/src/Math/AABB.hpp b/src/Math/AABB.hpp
index 11d26a8..19aa81c 100644
--- a/src/Math/AABB.hpp
+++ b/src/Math/AABB.hpp
@@ -8,6 +8,31 @@ struct AABB {
     AABB(Vector<3> min, Vector<3> max) : min(min), max(max) {}
     explicit AABB(Vector<3> max) : max(max) {}
 
+    Vector<3> size() const { return max - min; }
+    Vector<3> center() const { return (min + max) / 2; }
+
+    Bool contains(Vector<3> point) const {
+        return point.x() >= min.x() && point.x() <= max.x()
+            && point.y() >= min.y() && point.y() <= max.y()
+            && point.z() >= min.z() && point.z() <= max.z();
+    }
+
+    Bool intersects_on_x(AABB other) const {
+        return min.x() <= other.max.x() && max.x() >= other.min.x();
+    }
+
+    Bool intersects_on_y(AABB other) const {
+        return min.y() <= other.max.y() && max.y() >= other.min.y();
+    }
+
+    Bool intersects_on_z(AABB other) const {
+        return min.z() <= other.max.z() && max.z() >= other.min.z();
+    }
+
+    Bool collides(AABB other) const {
+        return intersects_on_x(other) && intersects_on_y(other) && intersects_on_z(other);
+    }
+
     std::array<Vector<3>, 8> corners() const {
         return {{
             {min.x(), min.y(), min.z()},
@@ -23,5 +48,12 @@ struct AABB {
 
     AABB offset(Vector<3> by) const { return {min + by, max + by}; }
 
+    AABB sum(AABB with) const {
+        auto new_size = size() + with.size();
+        return {center() - new_size / 2, center() + new_size / 2};
+    }
+
+    AABB cast_box(Vector<3> v, AABB against) const;
+
     Vector<3> min, max;
 };
diff --git a/src/Math/Ray.hpp b/src/Math/Ray.hpp
new file mode 100644
index 0000000..f83a2b5
--- /dev/null
+++ b/src/Math/Ray.hpp
@@ -0,0 +1,33 @@
+#pragma once
+
+#include "../Common/Lambda.hpp"
+#include "AABB.hpp"
+#include "Vector.hpp"
+
+struct Ray {
+    struct RaycastResult {
+        Bool hit = false;
+        Vec3 point;
+        Vec3 normal;
+    };
+
+    // https://gdbooks.gitbooks.io/3dcollisions/content/Chapter3/raycast_aabb.html
+    RaycastResult cast(AABB box) const {
+        Vec3 t_from = (box.min - origin) / direction;
+        Vec3 t_to = (box.max - origin) / direction;
+
+        Real t_min = t_from.zip(t_to, LAMBDA(std::min, 2)).reduce(LAMBDA(std::max, 2));
+        Real t_max = t_from.zip(t_to, LAMBDA(std::max, 2)).reduce(LAMBDA(std::min, 2));
+
+        if (t_max < 0 || t_min > t_max) return {};
+
+        return {
+            .hit = true,
+            .point = origin + direction * t_min,
+            .normal = t_from.zip(t_to, [](auto a, auto b) { return a < b ? -1.0 : 1.0; })
+        };
+    }
+
+    Vec3 origin;
+    Vec3 direction;
+};