servo_media_audio/
stereo_panner.rs

1use crate::block::{Chunk, Tick, FRAMES_PER_BLOCK};
2use crate::node::{AudioNodeEngine, BlockInfo};
3use crate::node::{AudioNodeType, ChannelInfo};
4use crate::param::{Param, ParamType};
5use std::f32::consts::PI;
6
7#[derive(Copy, Clone, Debug)]
8pub struct StereoPannerOptions {
9    pub pan: f32,
10}
11
12impl Default for StereoPannerOptions {
13    fn default() -> Self {
14        StereoPannerOptions { pan: 0. }
15    }
16}
17
18#[derive(AudioNodeCommon)]
19pub(crate) struct StereoPannerNode {
20    channel_info: ChannelInfo,
21    pan: Param,
22}
23
24impl StereoPannerNode {
25    pub fn new(options: StereoPannerOptions, channel_info: ChannelInfo) -> Self {
26        Self {
27            channel_info,
28            pan: Param::new(options.pan),
29        }
30    }
31
32    pub fn update_parameters(&mut self, info: &BlockInfo, tick: Tick) -> bool {
33        self.pan.update(info, tick)
34    }
35}
36
37impl AudioNodeEngine for StereoPannerNode {
38    fn node_type(&self) -> AudioNodeType {
39        AudioNodeType::StereoPannerNode
40    }
41
42    fn process(&mut self, mut inputs: Chunk, info: &BlockInfo) -> Chunk {
43        debug_assert!(inputs.len() == 1);
44
45        {
46            let block = &mut inputs.blocks[0];
47
48            block.explicit_repeat();
49
50            let mono = if block.chan_count() == 1 {
51                block.resize_silence(2);
52                true
53            } else {
54                debug_assert!(block.chan_count() == 2);
55                false
56            };
57
58            let (l, r) = block.data_mut().split_at_mut(FRAMES_PER_BLOCK.0 as usize);
59            let mut pan = self.pan.value();
60            for frame in 0..FRAMES_PER_BLOCK.0 {
61                let frame = Tick(frame);
62                if self.update_parameters(info, frame) {
63                    pan = self.pan.value();
64                }
65
66                // https://webaudio.github.io/web-audio-api/#stereopanner-algorithm
67
68                // clamp pan to [-1, 1]
69                pan = if pan < -1. {
70                    -1.
71                } else if pan > 1. {
72                    1.
73                } else {
74                    pan
75                };
76
77                let x = if mono {
78                    (pan + 1.) / 2.
79                } else if pan <= 0. {
80                    pan + 1.
81                } else {
82                    pan
83                };
84                let x = x * PI / 2.;
85
86                let mut gain_l = x.cos();
87                let mut gain_r = x.sin();
88                // 9. * PI / 2 is often slightly negative, clamp
89                if gain_l <= 0. {
90                    gain_l = 0.
91                }
92                if gain_r <= 0. {
93                    gain_r = 0.;
94                }
95
96                let index = frame.0 as usize;
97                if mono {
98                    let input = l[index];
99                    l[index] = input * gain_l;
100                    r[index] = input * gain_r;
101                } else if pan <= 0. {
102                    l[index] = l[index] + r[index] * gain_l;
103                    r[index] = r[index] * gain_r;
104                } else {
105                    r[index] = r[index] + l[index] * gain_r;
106                    l[index] = l[index] * gain_l;
107                }
108            }
109        }
110
111        inputs
112    }
113
114    fn input_count(&self) -> u32 {
115        1
116    }
117
118    fn get_param(&mut self, id: ParamType) -> &mut Param {
119        match id {
120            ParamType::Pan => &mut self.pan,
121            _ => panic!("Unknown param {:?} for PannerNode", id),
122        }
123    }
124}
servo_media_audio/stereo_panner.rs

servo_media_audio/
stereo_panner.rs
