1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144

use clamp::{Clamped, ClampedRange};
use math::{Clamp, FPoint3, FromSpace, FScalar, UPoint3};
use super::space::Axis;

/// Defines the bounds for `Offset` values.
#[derive(Clone, Copy)]
pub struct OffsetRange;

impl ClampedRange<u8> for OffsetRange {
    fn max_value() -> u8 {
        0x0F
    }

    fn min_value() -> u8 {
        0x00
    }
}

/// Edge offset.
///
/// This is the deformation of an `Edge` in a particular direction as an
/// absolute coordinate. It is used to define the endpoints of an `Edge`.
///
/// `Offset` is clamped to the open range `[0, 15]`. This is the same range that
/// the endpoints of an `Edge` are allowed to span.
pub type Offset = Clamped<u8, OffsetRange>;

/// Edge of a cube's `Geometry`.
///
/// `Edge`s define the endpoints of a cube's points along a particular axis as
/// front and back. For each axis, there are four edges describing the
/// coordinates of all eight points along that axis. The front and back of an
/// `Edge` are described by an `Offset` and affect opposing faces of a cube.
///
/// The front and back of an `Edge` cannot cross, but may intersect. These
/// values are packed into the upper and lower 4-bit halves of an `u8`.
#[derive(Copy, Clone)]
pub struct Edge(u8);

impl Edge {
    /// Constructs a new `Edge` that spans the full width (no deformation).
    fn full() -> Self {
        Edge(Offset::max_inner_value())
    }

    /// Constructs a new `Edge` that converges at a given `Offset`.
    fn converged(offset: Offset) -> Self {
        let offset = offset.to_inner();
        Edge((offset << 4) | offset)
    }

    /// Sets the offset of the front of the `Edge`. If the front would cross the
    /// back, it will be clamped such that it intersects the back.
    pub fn set_front(&mut self, offset: Offset) {
        let offset = offset.clamp(Offset::min_value(), self.back()).to_inner();
        self.0 = (offset << 4) | self.back().to_inner();
    }

    /// Sets the `Offset` of the back of the `Edge`. If the back would cross the
    /// front, it will be clamped such that it intersects the front.
    pub fn set_back(&mut self, offset: Offset) {
        let offset = offset.clamp(self.front(), Offset::max_value()).to_inner();
        self.0 = (self.front().to_inner() << 4) | offset;
    }

    /// Gets the `Offset` of the front of the `Edge`.
    pub fn front(&self) -> Offset {
        Offset::from((self.0 & 0xF0) >> 4)
    }

    /// Gets the `Offset` of the back of the `Edge`.
    pub fn back(&self) -> Offset {
        Offset::from(self.0 & 0x0F)
    }

    /// Gets the length of the `Edge`.
    pub fn length(&self) -> Offset {
        self.back() - self.front()
    }

    fn front_unit_transform(&self) -> FScalar {
        let min = Offset::min_inner_value();
        let n = (self.front().to_inner() - min) as FScalar;
        let d = (Offset::max_inner_value() - min) as FScalar;
        n / d
    }

    fn back_unit_transform(&self) -> FScalar {
        let min = Offset::min_inner_value();
        let span = Offset::max_inner_value() - min;
        let n = -((span - (self.back().to_inner() - min)) as FScalar);
        let d = span as FScalar;
        n / d
    }
}

#[derive(Copy, Clone)]
pub struct Geometry([[Edge; 4]; 3]);

impl Geometry {
    pub fn full() -> Self {
        Geometry([[Edge::full(); 4]; 3])
    }

    pub fn empty() -> Self {
        Geometry([[Edge::converged(Offset::from(0)); 4]; 3])
    }

    pub fn edges(&self, axis: Axis) -> &[Edge; 4] {
        &self.0[axis as usize]
    }

    pub fn edges_mut(&mut self, axis: Axis) -> &mut [Edge; 4] {
        &mut self.0[axis as usize]
    }

    pub fn is_empty(&self) -> bool {
        self.0
            .iter()
            .any(|axis| axis.iter().all(|edge| edge.length() == 0))
    }

    pub fn map_unit_cube_point(&self, unit: &UPoint3) -> FPoint3 {
        let mut point = FPoint3::from_space(*unit);
        for axis in Axis::range() {
            let edge = &self.0[axis][index_at_axis(axis, unit)];
            point[axis] += if unit[axis] == 0 {
                edge.front_unit_transform()
            }
            else {
                edge.back_unit_transform()
            };
        }
        point
    }
}

/// Gets the index of an `Edge` in a face (a collection of four `Edge`s along a
/// particular axis).
fn index_at_axis(axis: usize, unit: &UPoint3) -> usize {
    let p = if axis == 0 { 1 } else { 0 };
    let q = if axis == 2 { 1 } else { 2 };
    (unit[p] | (unit[q] << 1)) as usize
}