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* Convert Field into a trait * Box Field instances in Vec * Store bodies in Vec and implement update() * Add Environment constructor * Add Environment description * Update header file for Environment * Update ffi for Environment * Change return type of Distributor to Vec<Body> * Refactor gravitational force into new module * Add Attractor force * Replace sun with Attractor * Tidy up * Add Gravity tests * Add Attractor test * Remove unneccesary Body id * Guard against negative min_dist
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,177 @@ | ||
| use super::types::Body; | ||
| use geometry::types::{Point, Vector}; | ||
|
|
||
| // Gravity /////////////////////////////////////////////////////////////////// | ||
| // | ||
| // Newton's Law of Universal Gravitation. | ||
|
|
||
| pub struct Gravity { | ||
| g: f32, | ||
| min_dist: f32, | ||
| } | ||
|
|
||
| impl Gravity { | ||
| pub fn new(g: f32, min_dist: f32) -> Gravity { | ||
| if min_dist <= 0.0 { | ||
| panic!("The minimum gravitational distance \ | ||
| must be greater than 0. Got {}", min_dist); | ||
| } | ||
| Gravity { | ||
| g, | ||
| min_dist, | ||
| } | ||
| } | ||
|
|
||
| pub fn between(&self, b1: &Body, b2: &Body) -> Vector { | ||
| // Force is undefined for two bodies that occupy the same space. | ||
| if b1.position == b2.position { | ||
| return Vector::zero(); | ||
| } | ||
|
|
||
| let difference = Vector::difference(&b2.position, &b1.position); | ||
| let distance = difference.magnitude().max(self.min_dist); | ||
| let force = (self.g * b1.mass * b2.mass) / (distance * distance); | ||
|
|
||
| let direction = match difference.normalized() { | ||
| None => Vector::zero(), | ||
| Some(normalized) => normalized, | ||
| }; | ||
|
|
||
| &direction * force | ||
| } | ||
| } | ||
|
|
||
| // Attractor ///////////////////////////////////////////////////////////////// | ||
| // | ||
| // Gravitational attraction to a point. | ||
|
|
||
| pub struct Attractor { | ||
| body: Body, | ||
| gravity: Gravity, | ||
| } | ||
|
|
||
| impl Attractor { | ||
| pub fn new(mass: f32, point: Point, g: f32, min_dist: f32) -> Attractor { | ||
| Attractor { | ||
| body: Body::new(mass, point, Vector::zero()), | ||
| gravity: Gravity::new(g, min_dist), | ||
| } | ||
| } | ||
|
|
||
| pub fn force(&self, body: &Body) -> Vector { | ||
| self.gravity.between(body, &self.body) | ||
| } | ||
| } | ||
|
|
||
| // Tests ///////////////////////////////////////////////////////////////////// | ||
|
|
||
| #[cfg(test)] | ||
| mod tests { | ||
| use super::{Gravity, Attractor, Body}; | ||
| use geometry::types::{Point, Vector}; | ||
|
|
||
| #[test] | ||
| #[should_panic(expected = "The minimum gravitational distance must be greater than 0.")] | ||
| fn gravity_with_negative_minimum_distance() { | ||
| // given | ||
| Gravity::new(1.0, -2.0); | ||
| } | ||
|
|
||
| #[test] | ||
| fn gravity_calculates_force() { | ||
| // given | ||
| let sut = Gravity::new(1.5, 4.0); | ||
|
|
||
| let b1 = Body::new( | ||
| 1.0, | ||
| Point { x: 1.0, y: 2.0}, | ||
| Vector::zero() | ||
| ); | ||
|
|
||
| let b2 = Body::new( | ||
| 2.0, | ||
| Point { x: -3.5, y: 0.0}, | ||
| Vector::zero() | ||
| ); | ||
|
|
||
| // when | ||
| let result = sut.between(&b1, &b2); | ||
|
|
||
| // then | ||
| assert_eq!(result, Vector { dx: -0.1130488514, dy: -0.0502439339}); | ||
| } | ||
|
|
||
| #[test] | ||
| fn gravity_obeys_minimum_distance() { | ||
| // given | ||
| let sut = Gravity::new(1.5, 4.0); | ||
|
|
||
| let b1 = Body::new( | ||
| 1.0, | ||
| Point { x: 1.0, y: 2.0}, | ||
| Vector::zero() | ||
| ); | ||
|
|
||
| let b2 = Body::new( | ||
| 2.0, | ||
| Point { x: 2.0, y: 2.5}, | ||
| Vector::zero() | ||
| ); | ||
|
|
||
| assert!(b1.position.distance_to(&b2.position) < 4.0); | ||
|
|
||
| // when | ||
| let result = sut.between(&b1, &b2); | ||
|
|
||
| // then | ||
| let result_if_dist_was_4 = Vector { dx: 0.1677050983, dy: 0.0838525491}; | ||
| assert_eq!(result, result_if_dist_was_4); | ||
| } | ||
|
|
||
| #[test] | ||
| fn gravity_is_undefined_for_bodies_with_equal_position() { | ||
| // given | ||
| let sut = Gravity::new(1.5, 4.0); | ||
|
|
||
| let b1 = Body::new( | ||
| 1.0, | ||
| Point { x: 1.0, y: 2.0}, | ||
| Vector::zero() | ||
| ); | ||
|
|
||
| let b2 = Body::new( | ||
| 2.0, | ||
| Point { x: 1.0, y: 2.0}, | ||
| Vector::zero() | ||
| ); | ||
|
|
||
| // when | ||
| let result = sut.between(&b1, &b2); | ||
|
|
||
| // then | ||
| assert_eq!(result, Vector::zero()); | ||
| } | ||
|
|
||
| #[test] | ||
| fn attractor_calculates_force() { | ||
| // given | ||
| let sut = Attractor::new( | ||
| 100.0, | ||
| Point::origin(), | ||
| 2.3, | ||
| 1.0 | ||
| ); | ||
|
|
||
| let body = Body::new( | ||
| 3.8, | ||
| Point { x: 1.0, y: 2.0}, | ||
| Vector::zero() | ||
| ); | ||
|
|
||
| // when | ||
| let result = sut.force(&body); | ||
|
|
||
| // then | ||
| assert_eq!(result, Vector { dx: -78.17293649, dy: -156.345873}); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1 +1,2 @@ | ||
| pub mod types; | ||
| pub mod force; |
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