[Feature] Spatial/3D audio #116

Overview

Add positional audio support where sounds have a position in 3D space and are
panned/attenuated based on listener position and orientation.

Current State

Requires audio mixer implementation. No spatial audio exists.

Scope

• Set sound position in 3D space
• Set listener position and orientation
• Distance-based volume attenuation
• Stereo panning based on direction
• Configurable attenuation model

Non-Goals:

• HRTF (head-related transfer function) - complex, deferred
• Doppler effect (separate issue)
• Occlusion/obstruction (separate issue)
• Reverb zones (separate issue)

Proposed API

pub struct AudioListener {
  position: [f32; 3],
  forward: [f32; 3],
  up: [f32; 3],
}

pub struct SpatialSound {
  position: [f32; 3],
  min_distance: f32,
  max_distance: f32,
  // ...
}

impl SpatialSound {
  pub fn set_position(&mut self, position: [f32; 3]);
  pub fn set_min_distance(&mut self, distance: f32);
  pub fn set_max_distance(&mut self, distance: f32);
}

impl AudioContext {
  pub fn set_listener(&mut self, listener: AudioListener);
  pub fn play_spatial(&mut self, buffer: &SoundBuffer) -> SpatialSound;
}

Acceptance Criteria

• Sounds pan left/right based on listener orientation
• Sounds attenuate with distance
• Sounds beyond max_distance are silent
• Sounds within min_distance play at full volume
• Example with moving sound source

Affected Crates

lambda-rs, lambda-rs-platform

Notes

• Linear or inverse-square attenuation models
• Integrate with camera position for listener updates