Add empty cornell box with light and flipped normals.

rtiow/src/flip_normals.rs

@@ -0,0 +1,30 @@
+use aabb::AABB;
+use hitable::Hit;
+use hitable::HitRecord;
+use ray::Ray;
+
+pub struct FlipNormals {
+    hitable: Box<Hit>,
+}
+
+impl FlipNormals {
+    pub fn new(hitable: Box<Hit>) -> FlipNormals {
+        FlipNormals { hitable }
+    }
+}
+
+impl Hit for FlipNormals {
+    fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
+        if let Some(rec) = self.hitable.hit(r, t_min, t_max) {
+            return Some(HitRecord {
+                normal: -rec.normal,
+                ..rec
+            });
+        };
+        None
+    }
+
+    fn bounding_box(&self, t_min: f32, t_max: f32) -> Option<AABB> {
+        self.hitable.bounding_box(t_min, t_max)
+    }
+}