scena 1.1.0

A Rust-native scene-graph renderer with typed scene state, glTF assets, and explicit prepare/render lifecycles.
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
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163

use crate::material::Color;

use super::RasterTarget;
use super::color_contract::{
    aces_tonemap, apply_exposure, linear_rgba_to_srgb8, pbr_neutral_tonemap,
};

#[derive(Debug, Clone, Copy, PartialEq)]
pub(super) struct OutputTransform {
    exposure_ev: f32,
    tonemapper: Tonemapper,
}

impl OutputTransform {
    pub(super) fn encode_rgba8(self, color: Color) -> [u8; 4] {
        match self.tonemapper {
            Tonemapper::Aces => linear_rgba_to_srgb8(aces_tonemap(color, self.exposure_ev)),
            Tonemapper::PbrNeutral => {
                linear_rgba_to_srgb8(pbr_neutral_tonemap(color, self.exposure_ev))
            }
            Tonemapper::Standard => linear_rgba_to_srgb8(apply_exposure(color, self.exposure_ev)),
        }
    }

    pub(super) fn encode_clear_rgba8(self, color: Color) -> [u8; 4] {
        linear_rgba_to_srgb8(color)
    }

    pub(super) const fn exposure_ev(self) -> f32 {
        self.exposure_ev
    }

    pub(super) fn set_exposure_ev(&mut self, exposure_ev: f32) {
        self.exposure_ev = if exposure_ev.is_finite() {
            exposure_ev
        } else {
            0.0
        };
    }

    pub(super) const fn tonemapper(self) -> Tonemapper {
        self.tonemapper
    }

    pub(super) const fn set_tonemapper(&mut self, tonemapper: Tonemapper) {
        self.tonemapper = tonemapper;
    }

    pub(super) const fn color_management_uniform(self) -> [f32; 4] {
        match self.tonemapper {
            Tonemapper::Standard => [0.0, 0.0, 0.0, 0.0],
            Tonemapper::Aces => [1.0, 0.0, 0.0, 0.0],
            Tonemapper::PbrNeutral => [2.0, 0.0, 0.0, 0.0],
        }
    }
}

impl Default for OutputTransform {
    fn default() -> Self {
        Self {
            exposure_ev: 0.0,
            tonemapper: Tonemapper::PbrNeutral,
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum Tonemapper {
    Aces,
    Standard,
    #[default]
    PbrNeutral,
}

pub(super) fn apply_fxaa_rgba8(target: RasterTarget, frame: &mut [u8], scratch: &mut [u8]) -> u64 {
    if target.width < 3 || target.height < 3 {
        return 0;
    }
    debug_assert_eq!(frame.len(), target.byte_len());
    debug_assert_eq!(scratch.len(), target.byte_len());
    scratch.copy_from_slice(frame);

    for y in 1..target.height - 1 {
        for x in 1..target.width - 1 {
            let center = pixel_offset(target, x, y);
            let samples = [
                pixel_offset(target, x - 1, y - 1),
                pixel_offset(target, x, y - 1),
                pixel_offset(target, x + 1, y - 1),
                pixel_offset(target, x - 1, y),
                center,
                pixel_offset(target, x + 1, y),
                pixel_offset(target, x - 1, y + 1),
                pixel_offset(target, x, y + 1),
                pixel_offset(target, x + 1, y + 1),
            ];
            let center_luma = luma_from_srgb8(&scratch[center..center + 4]);
            let lumas = samples.map(|offset| luma_from_srgb8(&scratch[offset..offset + 4]));
            let min_luma = lumas.into_iter().fold(f32::INFINITY, f32::min);
            let max_luma = lumas.into_iter().fold(f32::NEG_INFINITY, f32::max);
            if max_luma - min_luma < FXAA_LUMA_THRESHOLD {
                continue;
            }
            let bright_neighbors = lumas
                .iter()
                .filter(|luma| **luma - center_luma >= FXAA_LUMA_THRESHOLD)
                .count();
            let dark_neighbors = lumas
                .iter()
                .filter(|luma| center_luma - **luma >= FXAA_LUMA_THRESHOLD)
                .count();
            let dark_edge =
                center_luma - min_luma <= FXAA_LOCAL_MIN_EPSILON && bright_neighbors >= 2;
            let light_edge =
                max_luma - center_luma <= FXAA_LOCAL_MIN_EPSILON && dark_neighbors >= 2;
            if !dark_edge && !light_edge {
                continue;
            }
            average_kernel_rgba8(scratch, frame, center, samples);
        }
    }

    1
}

fn pixel_offset(target: RasterTarget, x: u32, y: u32) -> usize {
    target.pixel_index(x, y) * 4
}

fn luma_from_srgb8(pixel: &[u8]) -> f32 {
    f32::from(pixel[0]) * 0.299 + f32::from(pixel[1]) * 0.587 + f32::from(pixel[2]) * 0.114
}

fn average_kernel_rgba8(
    source: &[u8],
    target: &mut [u8],
    output_offset: usize,
    sample_offsets: [usize; 9],
) {
    for channel in 0..4 {
        let sum: u16 = sample_offsets
            .into_iter()
            .map(|offset| u16::from(source[offset + channel]))
            .sum();
        target[output_offset + channel] = (sum / 9) as u8;
    }
}

const FXAA_LUMA_THRESHOLD: f32 = 16.0;
const FXAA_LOCAL_MIN_EPSILON: f32 = 1.0;

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn pbr_neutral_uses_dedicated_shader_branch_marker() {
        let mut output = OutputTransform::default();
        output.set_tonemapper(Tonemapper::PbrNeutral);

        assert_eq!(output.color_management_uniform(), [2.0, 0.0, 0.0, 0.0]);
    }
}