library: shape: add Shape trait definition

src/shape/mod.rs

@@ -0,0 +1,13 @@
+use super::{Point, Point2D, Vector};
+use bvh::aabb::Bounded;
+use bvh::ray::Ray;
+
+/// Represent an abstract shape inside the scene.
+pub trait Shape: Bounded + std::fmt::Debug {
+    /// Return the distance at which the object intersects with the ray, or None if it does not.
+    fn intersect(&self, ray: &Ray) -> Option<f64>;
+    /// Return the unit vector corresponding to the normal at this point of the shape.
+    fn normal(&self, point: &Point) -> Vector;
+    /// Project the point from the shape's surface to its texel coordinates.
+    fn project_texel(&self, point: &Point) -> Point2D;
+}