warped-sampling 0.1.0

Rust implementation of the Warped Sampling technique for mipmaps from http://graphics.ucsd.edu/~henrik/papers/wavelet_importance_sampling.pdf
Documentation 
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

#[derive(Debug, Copy, Clone)]
struct Box2f {
    min: (f64, f64),
    max: (f64, f64),
}

fn lerp(a: f64, b: f64, t: f64) -> f64 {
    a + t * (b - a)
}

fn lerp_factor(a: f64, b: f64, m: f64) -> f64 {
    (m - a) / (b - a)
}

fn set_box(i: usize, edge: [[f64; 2]; 3]) -> Box2f {
    let ox = i & 1;
    let oy = (i & 2) >> 1;
    Box2f {
        min: (edge[0 + ox][0], edge[0 + oy][1]),
        max: (edge[1 + ox][0], edge[1 + oy][1]),
    }
}

fn warp_a_point(point: (f64, f64), texture_region: &Box2f, warp: &Box2f) -> (f64, f64) {
    let xf = lerp_factor(warp.min.0, warp.max.0, point.0);
    let yf = lerp_factor(warp.min.1, warp.max.1, point.1);

    (
        lerp(texture_region.min.0, texture_region.max.0, xf),
        lerp(texture_region.min.1, texture_region.max.1, yf),
    )
}

pub fn warp(mipmaps: &Vec<&Vec<Vec<f64>>>, points: &[(f64, f64)], warped_points: &mut Vec<(f64, f64)>) {
    warp_recurse(
        &mipmaps,
        0,
        0,
        0,
        2,
        1.0,
        &Box2f {
            min: (0.0, 0.0),
            max: (1.0, 1.0),
        },
        &points,
        warped_points,
    );
}

fn warp_recurse(
    mipmaps: &Vec<&Vec<Vec<f64>>>,
    level: usize,
    x: usize,
    y: usize,
    w: usize,
    scale: f64,
    b: &Box2f,
    points: &[(f64, f64)],
    warped_points: &mut Vec<(f64, f64)>,
) {
    if level >= mipmaps.len() {
        let inv_size = 1.0 / ((1 << level + 1) as f64);

        let texture_box = Box2f {
            min: (x as f64 * inv_size, y as f64 * inv_size),
            max: ((x as f64 + 2.0) * inv_size, (y as f64 + 2.0) * inv_size),
        };

        for (x, y) in points {
            warped_points.push(warp_a_point((*x, *y), &texture_box, b))
        }

        return;
    }

    let cur_mip = &mipmaps[level];
    let pdfs = [
        scale * cur_mip[y][x],
        scale * cur_mip[y][x + 1],
        scale * cur_mip[y + 1][x],
        scale * cur_mip[y + 1][x + 1],
    ];

    let sum = 1.0 / (pdfs[0] + pdfs[1] + pdfs[2] + pdfs[3]);
    let mid_1 = sum * (pdfs[0] + pdfs[1]);
    let mid_0 = sum * pdfs[0] / mid_1;

    let mut edge = [
        [b.min.0, b.min.1],
        [lerp(b.min.0, b.max.0, mid_0), lerp(b.min.1, b.max.1, mid_1)],
        [b.max.0, b.max.1],
    ];

    let b0 = set_box(0, edge);
    let b1 = set_box(1, edge);

    let mid_2 = sum * pdfs[2] / (1.0 - mid_1);
    edge[1][0] = lerp(b.min.0, b.max.0, mid_2);

    let b2 = set_box(2, edge);
    let b3 = set_box(3, edge);

    let boxes = [b0, b1, b2, b3];

    let mut point_cache = [vec![], vec![], vec![], vec![]];

    for (x, y) in points {
        let mut offset = 0;
        offset += if *y > boxes[offset].max.1 { 2 } else { 0 };
        offset += if *x > boxes[offset].max.0 { 1 } else { 0 };
        point_cache[offset].push((*x, *y));
    }

    let nl = level + 1;
    let nx = x << 1;
    let ny = y << 1;
    let nw = w << 1;

    for idx in 0..4 {
        let ox = (idx & 1) << 1;
        let oy = idx & 2;
        if point_cache[idx].len() > 0 {
            warp_recurse(
                mipmaps,
                nl,
                nx + ox,
                ny + oy,
                nw,
                pdfs[idx],
                &boxes[idx],
                &point_cache[idx],
                warped_points,
            )
        }
    }
}