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

use std::time::Duration;

use crate::source::ChannelVolume;
use crate::{Sample, Source};

use super::SeekError;

/// A simple spatial audio source. The underlying source is transformed to Mono
/// and then played in stereo. The left and right channel's volume are amplified
/// differently depending on the distance of the left and right ear to the source.
#[derive(Clone)]
pub struct Spatial<I>
where
    I: Source,
    I::Item: Sample,
{
    input: ChannelVolume<I>,
}

fn dist_sq(a: [f32; 3], b: [f32; 3]) -> f32 {
    a.iter()
        .zip(b.iter())
        .map(|(a, b)| (a - b) * (a - b))
        .sum::<f32>()
}

impl<I> Spatial<I>
where
    I: Source,
    I::Item: Sample,
{
    /// Builds a new `SpatialSink`, beginning playback on a stream.
    pub fn new(
        input: I,
        emitter_position: [f32; 3],
        left_ear: [f32; 3],
        right_ear: [f32; 3],
    ) -> Spatial<I>
    where
        I: Source,
        I::Item: Sample,
    {
        let mut ret = Spatial {
            input: ChannelVolume::new(input, vec![0.0, 0.0]),
        };
        ret.set_positions(emitter_position, left_ear, right_ear);
        ret
    }

    /// Sets the position of the emitter and ears in the 3D world.
    pub fn set_positions(
        &mut self,
        emitter_pos: [f32; 3],
        left_ear: [f32; 3],
        right_ear: [f32; 3],
    ) {
        debug_assert!(left_ear != right_ear);
        let left_dist_sq = dist_sq(left_ear, emitter_pos);
        let right_dist_sq = dist_sq(right_ear, emitter_pos);
        let max_diff = dist_sq(left_ear, right_ear).sqrt();
        let left_dist = left_dist_sq.sqrt();
        let right_dist = right_dist_sq.sqrt();
        let left_diff_modifier = (((left_dist - right_dist) / max_diff + 1.0) / 4.0 + 0.5).min(1.0);
        let right_diff_modifier =
            (((right_dist - left_dist) / max_diff + 1.0) / 4.0 + 0.5).min(1.0);
        let left_dist_modifier = (1.0 / left_dist_sq).min(1.0);
        let right_dist_modifier = (1.0 / right_dist_sq).min(1.0);
        self.input
            .set_volume(0, left_diff_modifier * left_dist_modifier);
        self.input
            .set_volume(1, right_diff_modifier * right_dist_modifier);
    }
}

impl<I> Iterator for Spatial<I>
where
    I: Source,
    I::Item: Sample,
{
    type Item = I::Item;

    #[inline]
    fn next(&mut self) -> Option<I::Item> {
        self.input.next()
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.input.size_hint()
    }
}

impl<I> ExactSizeIterator for Spatial<I>
where
    I: Source + ExactSizeIterator,
    I::Item: Sample,
{
}

impl<I> Source for Spatial<I>
where
    I: Source,
    I::Item: Sample,
{
    #[inline]
    fn current_frame_len(&self) -> Option<usize> {
        self.input.current_frame_len()
    }

    #[inline]
    fn channels(&self) -> u16 {
        self.input.channels()
    }

    #[inline]
    fn sample_rate(&self) -> u32 {
        self.input.sample_rate()
    }

    #[inline]
    fn total_duration(&self) -> Option<Duration> {
        self.input.total_duration()
    }

    #[inline]
    fn try_seek(&mut self, pos: Duration) -> Result<(), SeekError> {
        self.input.try_seek(pos)
    }
}