1 files changed, 40 insertions, 0 deletions
diff --git a/src/hittable/instance/moving.rs b/src/hittable/instance/moving.rs
new file mode 100644
index 0000000..418fdbb
--- /dev/null
+++ b/src/hittable/instance/moving.rs
@@ -0,0 +1,40 @@
+use std::sync::Arc;
+
+use crate::{ray::Ray, vec3::Vec3};
+use crate::hittable::{HitRecord, Hittable, AABB};
+
+pub struct Moving {
+    pub hittable: Arc<dyn Hittable>,
+    pub offset_start: Vec3,
+    pub offset_end: Vec3,
+    pub time_start: f64,
+    pub time_end: f64,
+}
+
+impl Moving {
+    fn offset_at(&self, time: f64) -> Vec3 {
+        &self.offset_start + ((time - self.time_start) / (self.time_end - self.time_start)) * (&self.offset_end - &self.offset_start)
+    }
+}
+
+impl Hittable for Moving {
+    fn hit(&self, ray: &Ray, t_min: f64, t_max: f64) -> Option<HitRecord> {
+        let moved_ray = Ray { origin: &ray.origin - &self.offset_at(ray.time), direction: ray.direction.clone(), time: ray.time };
+        let mut hit_record = self.hittable.hit(&moved_ray, t_min, t_max)?;
+        hit_record.p += self.offset_at(ray.time).clone();
+        let normal = hit_record.normal.clone();
+        hit_record.set_face_normal(&moved_ray, &normal);
+        Some(hit_record)
+    }
+
+    fn bounding_box(&self, time_start: f64, time_end: f64) -> Option<AABB> {
+        let output_box = self.hittable.bounding_box(time_start, time_end)?;
+        Some(AABB {
+            minimum: &output_box.minimum + &self.offset_at(time_start),
+            maximum: &output_box.maximum + &self.offset_at(time_start),
+        }.surrounding_box(&AABB {
+            minimum: &output_box.minimum + &self.offset_at(time_end),
+            maximum: &output_box.maximum + &self.offset_at(time_end),
+        }))
+    }
+}