1 files changed, 29 insertions, 1 deletions

diff --git a/ray.h b/ray.h
index db28d0f..4d5401c 100644
--- a/ray.h
+++ b/ray.h
@@ -12,6 +12,7 @@ template<typename T>
 class ray3 {
     vec3<T> source_;
     vec3<T> direction_; // unit vector
+    double decay_; // How much power remaining
 
 public:
     ~ray3() = default;
@@ -23,27 +24,54 @@ public:
     ray3<T> &operator=(const ray3<T> &other) {
         source_ = other.source_;
         direction_ = other.direction_;
+        decay_ = other.decay_;
         return *this;
     }
 
-    ray3(const vec3<T> &source, const vec3<T> &direction) : source_(source), direction_(direction.unit_vec()) {}
+    ray3(const vec3<T> &source, const vec3<T> &direction) :
+            source_(source), direction_(direction.unit_vec()), decay_(1.0) {}
 
     // Get the source point from where the ray emits.
     vec3<T> source() const {
         return source_;
     }
 
+    void source(const vec3<T> &s) {
+        source_ = s;
+    }
+
     // Get the unit vector along the ray's direction.
     vec3<T> direction() const {
         return direction_;
     }
 
+    // d should be a unit vector
+    void direction(const vec3<T> &d) {
+        assert(fabs(d.mod2() - 1.0) < 1e-6);
+        direction_ = d;
+    }
+
     // Compute the point this ray reaches at the time `t`.
     template<typename U>
     vec3<T> at(U t) const {
         return source_ + direction_ * t;
     }
 
+    // Get the final color we got at the ray's origin, by tracing back along with the ray's path.
+    // Currently, here is only a simple power decay accumulation.
+    template<typename U>
+    pixel<U> hit(const pixel<U> &color) const {
+        return decay_ * color;
+    }
+
+    void decay(double a) {
+        decay_ *= a;
+    }
+
+    double decay() const {
+        return decay_;
+    }
+
     // Get a ray starts from zero and directs to undefined direction.
     static ray3<T> null() {
         return ray3<T>{vec3<T>::zero(), vec3<T>::zero()};