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// Dynamic physics body schema for a companion Prop.
use crate::{AssetId, AudioClipHandle, de_opt_asset_ref, de_opt_audio_clip_handle};
/// Makes a companion [Prop](#prop) a dynamic physics body.
///
/// Attach a PropBody to give a [Prop](#prop) real physics: it falls, collides,
/// stacks, tumbles, and (with `pickup: true` on the prop) can be carried and
/// thrown. A Prop with a `collider` but no PropBody is a static, immovable
/// obstacle.
///
/// ```json
/// {
/// "name": "crate_a_body",
/// "type": "PropBody",
/// "args": { "prop_name": "crate_a", "mass": 4.0, "friction": 0.6 }
/// }
/// ```
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
#[serde(default)]
pub struct PropBody {
/// The [Prop](#prop) this body drives. Must match a Prop declared in the
/// same world.
#[serde(deserialize_with = "de_opt_asset_ref")]
pub prop_name: Option<AssetId>,
/// Mass in kilograms. 0 lets the simulation derive mass from the collider
/// shape and a default density.
pub mass: f32,
/// Friction coefficient used for contacts with this body.
pub friction: f32,
/// Bounciness in [0, 1]. 0 is fully inelastic.
pub restitution: f32,
/// Multiplier applied to world gravity for this body. 1.0 is normal.
pub gravity_scale: f32,
/// Linear velocity damping, modelling air drag.
pub linear_damping: f32,
/// Optional [AudioClip](#audioclip) played at the contact point when this
/// body collides hard enough to pass the world's `contact_min_impulse`
/// (see [PhysicsConfig](#physicsconfig)). Louder impacts play louder.
#[serde(deserialize_with = "de_opt_audio_clip_handle")]
pub impact_clip: Option<AudioClipHandle>,
/// Linear gain applied to the impact clip at full impulse.
pub impact_volume: f32,
}
impl Default for PropBody {
fn default() -> Self {
Self {
prop_name: None,
mass: 0.0,
friction: 0.5,
restitution: 0.0,
gravity_scale: 1.0,
linear_damping: 0.05,
impact_clip: None,
impact_volume: 1.0,
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn a_blank_body_falls_under_full_gravity_without_bouncing() {
let b = PropBody::default();
assert_eq!(b.gravity_scale, 1.0);
assert_eq!(b.friction, 0.5);
assert_eq!(b.restitution, 0.0);
assert_eq!(b.linear_damping, 0.05);
// Zero mass means "derive it from the collider", not "massless".
assert_eq!(b.mass, 0.0);
assert!(b.prop_name.is_none());
}
#[test]
fn a_bouncy_floating_body_parses_and_round_trips_through_postcard() {
crate::test_support::install_resolvers();
let b: PropBody = serde_json::from_str(
r#"{"prop_name":"ball","mass":2.5,"friction":0.1,"restitution":0.9,
"gravity_scale":0,"linear_damping":0.2}"#,
)
.unwrap();
assert_eq!(b.prop_name, Some(AssetId(4)));
assert_eq!(b.gravity_scale, 0.0);
let bytes = postcard::to_allocvec(&b).unwrap();
let back: PropBody = postcard::from_bytes(&bytes).unwrap();
assert_eq!(back.prop_name, Some(AssetId(4)));
assert_eq!(back.mass, 2.5);
assert_eq!(back.friction, 0.1);
assert_eq!(back.restitution, 0.9);
assert_eq!(back.linear_damping, 0.2);
}
}