concinnity_asset/
prop_body.rs

1// Dynamic physics body schema for a companion Prop.
2
3use crate::{AssetId, AudioClipHandle, de_opt_asset_ref, de_opt_audio_clip_handle};
4
5/// Makes a companion [Prop](#prop) a dynamic physics body.
6///
7/// Attach a PropBody to give a [Prop](#prop) real physics: it falls, collides,
8/// stacks, tumbles, and (with `pickup: true` on the prop) can be carried and
9/// thrown. A Prop with a `collider` but no PropBody is a static, immovable
10/// obstacle.
11///
12/// ```json
13/// {
14///   "name": "crate_a_body",
15///   "type": "PropBody",
16///   "args": { "prop_name": "crate_a", "mass": 4.0, "friction": 0.6 }
17/// }
18/// ```
19#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
20#[serde(default)]
21pub struct PropBody {
22    /// The [Prop](#prop) this body drives. Must match a Prop declared in the
23    /// same world.
24    #[serde(deserialize_with = "de_opt_asset_ref")]
25    pub prop_name: Option<AssetId>,
26    /// Mass in kilograms. 0 lets the simulation derive mass from the collider
27    /// shape and a default density.
28    pub mass: f32,
29    /// Friction coefficient used for contacts with this body.
30    pub friction: f32,
31    /// Bounciness in [0, 1]. 0 is fully inelastic.
32    pub restitution: f32,
33    /// Multiplier applied to world gravity for this body. 1.0 is normal.
34    pub gravity_scale: f32,
35    /// Linear velocity damping, modelling air drag.
36    pub linear_damping: f32,
37    /// Optional [AudioClip](#audioclip) played at the contact point when this
38    /// body collides hard enough to pass the world's `contact_min_impulse`
39    /// (see [PhysicsConfig](#physicsconfig)). Louder impacts play louder.
40    #[serde(deserialize_with = "de_opt_audio_clip_handle")]
41    pub impact_clip: Option<AudioClipHandle>,
42    /// Linear gain applied to the impact clip at full impulse.
43    pub impact_volume: f32,
44}
45
46impl Default for PropBody {
47    fn default() -> Self {
48        Self {
49            prop_name: None,
50            mass: 0.0,
51            friction: 0.5,
52            restitution: 0.0,
53            gravity_scale: 1.0,
54            linear_damping: 0.05,
55            impact_clip: None,
56            impact_volume: 1.0,
57        }
58    }
59}
60
61#[cfg(test)]
62mod tests {
63    use super::*;
64
65    #[test]
66    fn a_blank_body_falls_under_full_gravity_without_bouncing() {
67        let b = PropBody::default();
68        assert_eq!(b.gravity_scale, 1.0);
69        assert_eq!(b.friction, 0.5);
70        assert_eq!(b.restitution, 0.0);
71        assert_eq!(b.linear_damping, 0.05);
72        // Zero mass means "derive it from the collider", not "massless".
73        assert_eq!(b.mass, 0.0);
74        assert!(b.prop_name.is_none());
75    }
76
77    #[test]
78    fn a_bouncy_floating_body_parses_and_round_trips_through_postcard() {
79        crate::test_support::install_resolvers();
80        let b: PropBody = serde_json::from_str(
81            r#"{"prop_name":"ball","mass":2.5,"friction":0.1,"restitution":0.9,
82                "gravity_scale":0,"linear_damping":0.2}"#,
83        )
84        .unwrap();
85        assert_eq!(b.prop_name, Some(AssetId(4)));
86        assert_eq!(b.gravity_scale, 0.0);
87
88        let bytes = postcard::to_allocvec(&b).unwrap();
89        let back: PropBody = postcard::from_bytes(&bytes).unwrap();
90        assert_eq!(back.prop_name, Some(AssetId(4)));
91        assert_eq!(back.mass, 2.5);
92        assert_eq!(back.friction, 0.1);
93        assert_eq!(back.restitution, 0.9);
94        assert_eq!(back.linear_damping, 0.2);
95    }
96}
concinnity_asset/prop_body.rs

concinnity_asset/
prop_body.rs
