plexus 0.0.10

3D mesh generation and manipulation.
Documentation 
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use decorum::R32;
use num::{One, Zero};

use geometry::{Duplet, Triplet};
use primitive::generate::{
    Generate, IndexGenerator, IndexPolygonGenerator, PolygonGenerator, PositionGenerator,
    PositionPolygonGenerator, PositionVertexGenerator, TextureGenerator, TexturePolygonGenerator,
    VertexGenerator,
};
use primitive::topology::{MapVerticesInto, Quad};
use primitive::Half;

#[derive(Clone, Copy, Eq, Hash, PartialEq)]
pub enum Plane {
    XY,
    NXY,
    ZY,
    NZY,
    XZ,
    XNZ,
}

#[derive(Clone, Copy)]
pub struct Bounds {
    lower: R32,
    upper: R32,
}

impl Bounds {
    pub fn unit_radius() -> Self {
        Bounds {
            lower: -R32::one(),
            upper: R32::one(),
        }
    }

    pub fn unit_width() -> Self {
        Bounds {
            lower: -R32::half(),
            upper: R32::half(),
        }
    }
}

impl Default for Bounds {
    fn default() -> Self {
        Self::unit_width()
    }
}

#[derive(Clone, Copy)]
pub struct Cube;

impl Cube {
    pub fn new() -> Self {
        Cube
    }

    pub fn polygons_with_plane(&self) -> Generate<Self, (), Quad<Plane>> {
        Generate::new(
            self,
            (),
            0..self.polygon_count(),
            Cube::polygon_with_plane_from,
        )
    }

    fn polygon_with_plane_from(&self, _: &(), index: usize) -> Quad<Plane> {
        match index {
            0 => Quad::converged(Plane::XY),  // front
            1 => Quad::converged(Plane::NZY), // right
            2 => Quad::converged(Plane::XNZ), // top
            3 => Quad::converged(Plane::ZY),  // left
            4 => Quad::converged(Plane::XZ),  // bottom
            5 => Quad::converged(Plane::NXY), // back
            _ => panic!(),
        }
    }
}

impl Default for Cube {
    fn default() -> Self {
        Cube::new()
    }
}

impl VertexGenerator for Cube {
    fn vertex_count(&self) -> usize {
        8
    }
}

impl PolygonGenerator for Cube {
    fn polygon_count(&self) -> usize {
        6
    }
}

impl PositionGenerator for Cube {
    type State = Bounds;
}

impl PositionVertexGenerator for Cube {
    type Output = Triplet<R32>;

    #[cfg_attr(rustfmt, rustfmt_skip)]
    fn vertex_with_position_from(&self, state: &Self::State, index: usize) -> Self::Output {
        let x = if index & 0b100 == 0b100 { state.upper } else { state.lower };
        let y = if index & 0b010 == 0b010 { state.upper } else { state.lower };
        let z = if index & 0b001 == 0b001 { state.upper } else { state.lower };
        Triplet(x, y, z)
    }
}

impl PositionPolygonGenerator for Cube {
    type Output = Quad<Triplet<R32>>;

    fn polygon_with_position_from(&self, state: &Self::State, index: usize) -> Self::Output {
        self.polygon_with_index_from(&Default::default(), index)
            .map_vertices_into(|index| self.vertex_with_position_from(state, index))
    }
}

impl IndexGenerator for Cube {
    type State = ();
}

impl IndexPolygonGenerator for Cube {
    type Output = Quad<usize>;

    fn polygon_with_index_from(
        &self,
        _: &Self::State,
        index: usize,
    ) -> <Self as IndexPolygonGenerator>::Output {
        match index {
            0 => Quad::new(5, 7, 3, 1), // front
            1 => Quad::new(6, 7, 5, 4), // right
            2 => Quad::new(3, 7, 6, 2), // top
            3 => Quad::new(0, 1, 3, 2), // left
            4 => Quad::new(4, 5, 1, 0), // bottom
            5 => Quad::new(0, 2, 6, 4), // back
            _ => panic!(),
        }
    }
}

impl TextureGenerator for Cube {
    type State = ();
}

impl TexturePolygonGenerator for Cube {
    type Output = Quad<Duplet<R32>>;

    fn polygon_with_texture_from(
        &self,
        _: &Self::State,
        index: usize,
    ) -> <Self as TexturePolygonGenerator>::Output {
        let uu = Duplet(One::one(), One::one());
        let ul = Duplet(One::one(), Zero::zero());
        let ll = Duplet(Zero::zero(), Zero::zero());
        let lu = Duplet(Zero::zero(), One::one());
        match index {
            0 | 4 | 5 => Quad::new(uu, ul, ll, lu), // front | bottom | back
            1 => Quad::new(ul, ll, lu, uu),         // right
            2 | 3 => Quad::new(lu, uu, ul, ll),     // top | left
            _ => panic!(),
        }
    }
}