diff --git a/src/bin/flat.rs b/src/bin/flat.rs
index d4592a8..f4e6152 100644
--- a/src/bin/flat.rs
+++ b/src/bin/flat.rs
@@ -222,11 +222,164 @@ impl Metric for Coil {
 	}
 }
 
+#[derive(Debug, PartialEq)]
 struct Ray {
 	pos: Vec2,
 	dir: Vec2,
 }
 
+mod basic_shapes {
+	use glam::{Vec2, vec2};
+	use crate::{Ray, shape};
+
+	pub struct Rect {
+		pub size: Vec2,
+	}
+
+	impl Rect {
+		/// Отражает луч, чтобы все координаты направления были положительны (допустимо благодаря симметрии Rect).
+		fn flip_ray(ray: Ray) -> Ray {
+			Ray { pos: ray.pos * ray.dir.signum(), dir: ray.dir.abs() }
+		}
+	}
+
+	impl shape::Shape for Rect {
+		fn is_inside(&self, pt: Vec2) -> bool {
+			pt.abs().cmplt(self.size).all()
+		}
+
+		fn trace_into(&self, ray: Ray) -> Option<f32> {
+			let ray = Self::flip_ray(ray);
+			// ray.pos.x + t * ray.dir.x = −size.x
+			let ts = (-self.size - ray.pos) / ray.dir;
+			let t = ts.max_element();
+			let pt = ray.pos + t * ray.dir;
+			if t < 0.0 { return None; }
+			if pt.cmpgt(self.size).any() { return None; }
+			Some(t)
+		}
+
+		fn trace_out_of(&self, ray: Ray) -> Option<f32> {
+			let ray = Self::flip_ray(ray);
+			// ray.pos.x + t * ray.dir.x = +size.x
+			let ts = (self.size - ray.pos) / ray.dir;
+			let t = ts.min_element();
+			Some(t)
+		}
+
+		fn visualise(&self) -> Vec<Vec2> {
+			vec![vec2(-self.size.x, -self.size.y), vec2(self.size.x, -self.size.y), vec2(self.size.x, self.size.y), vec2(-self.size.x, self.size.y)]
+		}
+	}
+
+	#[cfg(test)]
+	use crate::shape::Shape;
+
+	#[test]
+	fn test_rect() {
+		assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 5.0) }), Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 5.0) });
+		assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(-4.0, 5.0) }), Ray { pos: vec2(-2.0, 3.0), dir: vec2(4.0, 5.0) });
+		assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, -5.0) }), Ray { pos: vec2(2.0, -3.0), dir: vec2(4.0, 5.0) });
+		assert_eq!(Rect::flip_ray(Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 0.0) }), Ray { pos: vec2(2.0, 3.0), dir: vec2(4.0, 0.0) });
+
+		let r = Rect { size: vec2(2.0, 3.0) };
+
+		assert_eq!(r.trace_into(Ray { pos: vec2(3.0, 3.0), dir: vec2(1.0, 1.0) }), None);
+		assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 2.0), dir: vec2(1.0, 0.0) }), Some(1.0));
+		assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 2.0), dir: vec2(-1.0, 0.0) }), None);
+		assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 1.0), dir: vec2(2.0, 2.0) }), Some(0.5));
+		assert_eq!(r.trace_into(Ray { pos: vec2(-3.0, 2.1), dir: vec2(2.0, 2.0) }), None);
+
+		assert_eq!(r.trace_into(Ray { pos: vec2(2.0, 3.0), dir: vec2(1.0, 1.0) }), None);
+		assert_eq!(r.trace_into(Ray { pos: vec2(-2.0, 3.0), dir: vec2(-1.0, 1.0) }), None);
+		assert_eq!(r.trace_into(Ray { pos: vec2(2.0, 3.0), dir: vec2(-1.0, -1.0) }), Some(0.0));
+		assert_eq!(r.trace_into(Ray { pos: vec2(2.0, -3.0), dir: vec2(-1.0, 1.0) }), Some(0.0));
+
+		assert_eq!(r.trace_out_of(Ray { pos: vec2(0.0, 0.0), dir: vec2(1.0, 1.0) }), Some(2.0));
+		assert_eq!(r.trace_out_of(Ray { pos: vec2(0.0, 0.0), dir: vec2(0.0, 1.0) }), Some(3.0));
+		assert_eq!(r.trace_out_of(Ray { pos: vec2(0.0, 1.0), dir: vec2(0.0, -1.0) }), Some(4.0));
+		assert_eq!(r.trace_out_of(Ray { pos: vec2(1.0, 1.0), dir: vec2(0.0, -1.0) }), Some(4.0));
+		assert_eq!(r.trace_out_of(Ray { pos: vec2(2.0, 3.0), dir: vec2(1.0, 1.0) }), Some(0.0));
+	}
+}
+
+mod shape {
+	use glam::{Affine2, Vec2};
+	use crate::Ray;
+
+	pub trait Shape {
+		fn is_inside(&self, pt: Vec2) -> bool;
+
+		/// Ищет ближайшее пересечение луча с границей в направлении внутрь контура. Возвращает расстояние (в ray.dir).
+		fn trace_into(&self, ray: Ray) -> Option<f32>;
+		/// Ищет ближайшее пересечение луча с границей в направлении вовне контура. Возвращает расстояние (в ray.dir).
+		fn trace_out_of(&self, ray: Ray) -> Option<f32>;
+
+		/// Возвращает визуальное представление контура, для отладки.
+		fn visualise(&self) -> Vec<Vec2>;
+	}
+
+	pub struct MovedShape<S: Shape> {
+		pub shape: S,
+		pub transform: Affine2, // transform(координаты контура) = 0
+	}
+
+	impl<S: Shape> MovedShape<S> {
+		fn pt_to_inner(&self, pt: Vec2) -> Vec2 {
+			self.transform.transform_point2(pt)
+		}
+		fn pt_to_outer(&self, pt: Vec2) -> Vec2 {
+			self.transform.inverse().transform_point2(pt)
+		}
+		fn vec_to_inner(&self, vec: Vec2) -> Vec2 {
+			self.transform.transform_vector2(vec)
+		}
+		fn vec_to_outer(&self, vec: Vec2) -> Vec2 {
+			self.transform.inverse().transform_vector2(vec)
+		}
+		fn ray_to_inner(&self, ray: Ray) -> Ray {
+			Ray { pos: self.pt_to_inner(ray.pos), dir: self.vec_to_inner(ray.dir) }
+		}
+		fn ray_to_outer(&self, ray: Ray) -> Ray {
+			Ray { pos: self.pt_to_outer(ray.pos), dir: self.vec_to_outer(ray.dir) }
+		}
+	}
+
+	impl<S: Shape> Shape for MovedShape<S> {
+		fn is_inside(&self, pt: Vec2) -> bool {
+			self.shape.is_inside(self.pt_to_inner(pt))
+		}
+		fn trace_into(&self, ray: Ray) -> Option<f32> {
+			self.shape.trace_into(self.ray_to_inner(ray))
+		}
+		fn trace_out_of(&self, ray: Ray) -> Option<f32> {
+			self.shape.trace_out_of(self.ray_to_inner(ray))
+		}
+		fn visualise(&self) -> Vec<Vec2> {
+			self.shape.visualise().iter().map(|pt| self.pt_to_outer(*pt)).collect()
+		}
+	}
+
+	pub struct InvertedShape<S: Shape> {
+		pub shape: S,
+	}
+
+	impl<S: Shape> Shape for InvertedShape<S> {
+		fn is_inside(&self, pt: Vec2) -> bool {
+			!self.shape.is_inside(pt)
+		}
+		fn trace_into(&self, ray: Ray) -> Option<f32> {
+			self.shape.trace_out_of(ray)
+		}
+		fn trace_out_of(&self, ray: Ray) -> Option<f32> {
+			self.shape.trace_into(ray)
+		}
+		fn visualise(&self) -> Vec<Vec2> {
+			self.shape.visualise()
+		}
+	}
+}
+
 struct Grid {
 	hlines: Vec<f32>,
 	vlines: Vec<f32>,