auburn 0.1.4

Fast and simple physics library.
Documentation 
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use super::*;

/// 2D rectangle *centered at the origin*.
#[derive(Default, Clone, Copy, PartialEq, Debug)]
#[cfg_attr(feature = "bevy", derive(bevy::prelude::Component))]
pub struct Box2d {
    pub halfsize: Vec2,
}

impl Box2d {
    pub const fn with_halfdims(x: f32, y: f32) -> Self {
        Self::new(Vec2::new(x, y))
    }
    pub const fn new(halfsize: Vec2) -> Self {
        Self { halfsize }
    }
    pub fn cover(&mut self, point: &Vec2) {
        let x = point.x.abs();
        let y = point.y.abs();
        self.halfsize.x = self.halfsize.x.max(x);
        self.halfsize.y = self.halfsize.y.max(y);
    }
}

//

impl SymmetricBoundingBox2d for Box2d {
    fn symmetric_bounding_box(&self) -> Box2d {
        *self
    }
}

impl ExtremePoint2d for Box2d {
    fn extreme_point(&self, direction: Vec2) -> Vec2 {
        Vec2::new(
            if direction.x > 0.0 {
                self.halfsize.x
            } else {
                -self.halfsize.x
            },
            if direction.y > 0.0 {
                self.halfsize.y
            } else {
                -self.halfsize.y
            },
        )
    }
}

impl MinkowskiNegationIsIdentity for Box2d {}

impl MinkowskiSum<Box2d> for Box2d {
    type Output = Self;

    fn minkowski_sum(&self, t: &Box2d) -> Self::Output {
        Self::Output {
            halfsize: self.halfsize + t.halfsize,
        }
    }
}

impl MinkowskiSum<Ball> for Box2d {
    type Output = RoundedBox2d;
    fn minkowski_sum(&self, t: &Ball) -> Self::Output {
        Self::Output {
            halfsize: self.halfsize,
            radius: t.radius,
        }
    }
}

impl DefaultCol2dImpls for Box2d {}

// Collides

impl CollidesRel2d<Point> for Box2d {
    fn collides_rel(&self, _t: &Point, rel: &impl Transformation2d) -> bool {
        let delta = rel.apply_origin();
        -self.halfsize.x < delta.x
            && delta.x < self.halfsize.x
            && -self.halfsize.y < delta.y
            && delta.y < self.halfsize.y
    }
}

// Penetrates

impl PenetratesRel2d<Point> for Box2d {
    fn penetrates_rel(&self, t: &Point, rel: &impl Transformation2d) -> Option<Vec2> {
        if self.collides_rel(t, rel) {
            let delta = rel.apply_origin();
            let delta_x = delta.x.abs() - self.halfsize.x;
            let delta_y = delta.y.abs() - self.halfsize.y;

            if delta_x > delta_y {
                Some(Vec2::new(delta_x * delta.x.signum(), 0.0))
            } else {
                Some(Vec2::new(0.0, delta_y * delta.y.signum()))
            }
        } else {
            None
        }
    }
}

// Sdf

impl SdfRel2d<Point> for Box2d {
    fn sdf_rel(&self, t: &Point, rel: &impl Transformation2d) -> f32 {
        let delta = rel.apply_origin();
        let delta_x = delta.x.abs() - self.halfsize.x;
        let delta_y = delta.y.abs() - self.halfsize.y;

        if self.collides_rel(t, rel) {
            delta_x.max(delta_y)
        } else {
            if delta_x < 0.0 {
                delta_y
            } else if delta_y < 0.0 {
                delta_x
            } else {
                Vec2::new(delta_x, delta_y).length()
            }
        }
    }
}

// Sdf Vector

impl SdfRel2dVector<Point> for Box2d {
    fn sdfv_rel(&self, t: &Point, rel: &impl Transformation2d) -> Vec2 {
        let delta = rel.apply_origin();
        let delta_x = delta.x.abs() - self.halfsize.x;
        let delta_y = delta.y.abs() - self.halfsize.y;

        if self.collides_rel(t, rel) {
            if delta_x > delta_y {
                Vec2::new(delta_x * delta.x.signum(), 0.0)
            } else {
                Vec2::new(0.0, delta_y * delta.y.signum())
            }
        } else {
            let delta_x = delta_x.max(0.0);
            let delta_y = delta_y.max(0.0);
            Vec2::new(delta_x * delta.x.signum(), delta_y * delta.y.signum())
        }
    }
}

#[cfg(test)]
mod tests {
    use approx::assert_relative_eq;

    use super::*;

    #[test]
    fn point_v_box_collides() {
        let b = Box2d::with_halfdims(2.0, 1.0);
        let y1 = Vec2::new(0.0, 0.0);
        let y2 = Vec2::new(1.5, 0.0);
        let y3 = Vec2::new(0.0, -0.5);
        let n1 = Vec2::new(3.0, 0.0);
        let n2 = Vec2::new(0.0, 2.0);
        let n3 = Vec2::new(-3.0, 0.0);
        let n4 = Vec2::new(0.0, -2.0);
        let n5 = Vec2::new(-2.1, 1.1);

        assert!(b.collides_rel(&Point, &y1));
        assert!(b.collides_rel(&Point, &y2));
        assert!(b.collides_rel(&Point, &y3));

        assert!(Point.collides_rel(&b, &y1));
        assert!(Point.collides_rel(&b, &y2));
        assert!(Point.collides_rel(&b, &y3));

        assert!(!b.collides_rel(&Point, &n1));
        assert!(!b.collides_rel(&Point, &n2));
        assert!(!b.collides_rel(&Point, &n3));
        assert!(!b.collides_rel(&Point, &n4));
        assert!(!b.collides_rel(&Point, &n5));

        assert!(!Point.collides_rel(&b, &n1));
        assert!(!Point.collides_rel(&b, &n2));
        assert!(!Point.collides_rel(&b, &n3));
        assert!(!Point.collides_rel(&b, &n4));
        assert!(!Point.collides_rel(&b, &n5));
    }

    #[test]
    fn point_v_box_penetrates() {
        let b = Box2d::with_halfdims(2.0, 1.0);
        let y1 = Vec2::new(0.0, 0.0);
        let y2 = Vec2::new(1.5, 0.0);
        let y3 = Vec2::new(0.0, -0.5);
        let n1 = Vec2::new(3.0, 0.0);
        let n2 = Vec2::new(0.0, 2.0);
        let n3 = Vec2::new(-3.0, 0.0);
        let n4 = Vec2::new(0.0, -2.0);
        let n5 = Vec2::new(-2.1, 1.1);

        // TODO(lubo): Actualy check if this is reasonable
        assert!(b.penetrates_rel(&Point, &y1).is_some());
        assert!(Point.penetrates_rel(&b, &y1).is_some());

        // assert_eq!(b.penetrates(&Point, &y2), Some(Vec2::new(0.5, 0.0)));
        // assert_eq!(Point.penetrates(&b, &y2), Some(Vec2::new(0.5, 0.0)));
        assert_eq!(b.penetrates_rel(&Point, &y2), Some(Vec2::new(-0.5, 0.0)));
        assert_eq!(Point.penetrates_rel(&b, &y2), Some(Vec2::new(-0.5, 0.0)));

        // assert_eq!(b.penetrates(&Point, &y3), Some(Vec2::new(0.0, -0.5)));
        // assert_eq!(Point.penetrates(&b, &y3), Some(Vec2::new(0.0, -0.5)));
        assert_eq!(b.penetrates_rel(&Point, &y3), Some(Vec2::new(0.0, 0.5)));
        assert_eq!(Point.penetrates_rel(&b, &y3), Some(Vec2::new(0.0, 0.5)));

        assert_eq!(None, b.penetrates_rel(&Point, &n1));
        assert_eq!(None, b.penetrates_rel(&Point, &n2));
        assert_eq!(None, b.penetrates_rel(&Point, &n3));
        assert_eq!(None, b.penetrates_rel(&Point, &n4));
        assert_eq!(None, b.penetrates_rel(&Point, &n5));

        assert_eq!(None, Point.penetrates_rel(&b, &n1));
        assert_eq!(None, Point.penetrates_rel(&b, &n2));
        assert_eq!(None, Point.penetrates_rel(&b, &n3));
        assert_eq!(None, Point.penetrates_rel(&b, &n4));
        assert_eq!(None, Point.penetrates_rel(&b, &n5));
    }

    #[test]
    fn point_v_box_sdf() {
        let b = Box2d::with_halfdims(2.0, 1.0);
        let y1 = Vec2::new(0.0, 0.0);
        let y2 = Vec2::new(1.5, 0.0);
        let y3 = Vec2::new(0.0, -0.5);
        let n1 = Vec2::new(3.0, 0.0);
        let n2 = Vec2::new(0.0, 2.0);
        let n3 = Vec2::new(-3.0, 0.0);
        let n4 = Vec2::new(0.0, -2.0);
        let n5 = Vec2::new(-2.1, 1.1);

        assert_eq!(b.sdf_rel(&Point, &y1), -1.0);
        assert_eq!(b.sdf_rel(&Point, &y2), -0.5);
        assert_eq!(b.sdf_rel(&Point, &n1), 1.0);
        assert_eq!(b.sdf_rel(&Point, &n2), 1.0);
        assert_eq!(b.sdf_rel(&Point, &n3), 1.0);
        assert_eq!(b.sdf_rel(&Point, &n4), 1.0);
        assert_relative_eq!(b.sdf_rel(&Point, &n5), 0.1414213);
    }

    #[test]
    fn box_v_box_no_collision() {
        let b = Box2d::with_halfdims(0.5, 0.5);
        let delta = Vec2::new(2.0, 0.0);
        assert!(!b.collides_rel(&b, &delta));
        assert_eq!(b.penetrates_rel(&b, &delta), None);
    }

    #[test]
    fn box_v_box_perfect_overlap() {
        let b = Box2d::with_halfdims(0.5, 0.5);
        let delta = Vec2::new(0.0, 0.0);
        assert!(b.collides_rel(&b, &delta));
        // TODO(lubo): Actualy check if this is reasonable
        assert!(b.penetrates_rel(&b, &delta).is_some());
    }

    #[test]
    fn box_v_box_collision() {
        let b = Box2d::with_halfdims(0.5, 0.5);
        for i in 1..=9 {
            let delta = Vec2::new(i as f32 / 10.0, 0.0);
            assert!(b.collides_rel(&b, &delta));
            // assert_eq!(Some(Vec2::new(1.0, 0.0) - delta), b.penetrates(&b, &delta));
            assert_eq!(Some(delta - Vec2::new(1.0, 0.0)), b.penetrates_rel(&b, &delta));
        }
    }
}