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use crate::dynamics::MassProperties;
#[cfg(feature = "dim3")]
use crate::geometry::Capsule;
use crate::math::{Point, PrincipalAngularInertia, Vector};
impl MassProperties {
fn cylinder_y_volume_unit_inertia(
half_height: f32,
radius: f32,
) -> (f32, PrincipalAngularInertia<f32>) {
#[cfg(feature = "dim2")]
{
Self::cuboid_volume_unit_inertia(Vector::new(radius, half_height))
}
#[cfg(feature = "dim3")]
{
let volume = half_height * radius * radius * std::f32::consts::PI * 2.0;
let sq_radius = radius * radius;
let sq_height = half_height * half_height * 4.0;
let off_principal = (sq_radius * 3.0 + sq_height) / 12.0;
let inertia = Vector::new(off_principal, sq_radius / 2.0, off_principal);
(volume, inertia)
}
}
pub(crate) fn from_capsule(density: f32, a: Point<f32>, b: Point<f32>, radius: f32) -> Self {
let half_height = (b - a).norm() / 2.0;
let (cyl_vol, cyl_unit_i) = Self::cylinder_y_volume_unit_inertia(half_height, radius);
let (ball_vol, ball_unit_i) = Self::ball_volume_unit_angular_inertia(radius);
let cap_vol = cyl_vol + ball_vol;
let cap_mass = cap_vol * density;
let mut cap_unit_i = cyl_unit_i + ball_unit_i;
let local_com = na::center(&a, &b);
#[cfg(feature = "dim2")]
{
let h = half_height * 2.0;
let extra = h * h * 0.5 + h * radius * 3.0 / 8.0;
cap_unit_i += extra;
Self::new(local_com, cap_mass, cap_unit_i * cap_mass)
}
#[cfg(feature = "dim3")]
{
let h = half_height * 2.0;
let extra = h * h * 0.5 + h * radius * 3.0 / 8.0;
cap_unit_i.x += extra;
cap_unit_i.z += extra;
let local_frame = Capsule::new(a, b, radius).rotation_wrt_y();
Self::with_principal_inertia_frame(
local_com,
cap_mass,
cap_unit_i * cap_mass,
local_frame,
)
}
}
}
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