brep_kernel/props/
mass_properties.rs

1use crate::topology::{BrepSolid, EdgeRecord, FaceRecord, ShellRecord};
2use crate::{NurbsCurve, NurbsSurface, Vec3};
3use serde::Serialize;
4
5/// Eight-station Gauss–Legendre on `[-1, 1]`. `pub(crate)` because
6/// `brep/soundness.rs`'s vector-area closure integrates the trims with the
7/// same rule the mass integrals use — one table, not a third copy of it.
8pub(crate) const GAUSS_X: [f64; 8] = [
9    -0.9602898564975363,
10    -0.7966664774136267,
11    -0.525532409916329,
12    -0.18343464249564978,
13    0.18343464249564978,
14    0.525532409916329,
15    0.7966664774136267,
16    0.9602898564975363,
17];
18pub(crate) const GAUSS_W: [f64; 8] = [
19    0.10122853629037669,
20    0.22238103445337445,
21    0.31370664587788727,
22    0.362683783378362,
23    0.362683783378362,
24    0.31370664587788727,
25    0.22238103445337445,
26    0.10122853629037669,
27];
28
29#[derive(Clone, Copy)]
30enum Integrand {
31    Area,
32    Volume,
33    VolumeAbout(Vec3),
34    /// Divergence-theorem first moments: ∫x dV = ∮ (x²/2)·nx dA, etc.
35    MomentX,
36    MomentY,
37    MomentZ,
38    /// Second moments: ∫x² dV = ∮ (x³/3)·nx dA, etc.
39    SecondXX,
40    SecondYY,
41    SecondZZ,
42    /// Products: ∫xy dV = ∮ (x²y/2)·nx dA, ∫xz, ∫yz analogously.
43    ProductXY,
44    ProductXZ,
45    ProductYZ,
46}
47
48/// A bounded, per-solid memo for exact area and volume. Geometry edits are
49/// detected by the face-set content identity; callers never invalidate it.
50/// The contents are private so external code cannot supply a fabricated result.
51#[derive(Clone, Debug, Default)]
52pub struct MassPropertiesCache {
53    entry: std::cell::Cell<Option<(FaceSetIdentity, MassProperties)>>,
54}
55
56#[derive(Clone, Copy, Debug, Serialize)]
57pub struct MassProperties {
58    pub surface_area: f64,
59    pub volume: f64,
60}
61
62#[derive(Clone, Copy, Debug, Serialize)]
63pub struct FullMassProperties {
64    pub surface_area: f64,
65    pub volume: f64,
66    /// Volume centroid (unit density center of mass).
67    pub centroid: Vec3,
68    /// Inertia tensor about the centroid for unit density, row-major
69    /// [[Ixx, Ixy, Ixz], [Ixy, Iyy, Iyz], [Ixz, Iyz, Izz]].
70    pub inertia: [[f64; 3]; 3],
71    /// Principal moments of inertia (eigenvalues of `inertia`) at unit
72    /// density, sorted ASCENDING: `principal_moments[0] <= [1] <= [2]`.
73    /// Golovanov §8.11.
74    pub principal_moments: [f64; 3],
75    /// Principal axes of inertia (eigenvectors of `inertia`), one per row:
76    /// `principal_axes[i]` is the unit axis whose moment is
77    /// `principal_moments[i]`. The three axes are orthonormal and arranged as
78    /// a RIGHT-HANDED frame (determinant +1); the sign of the third axis is
79    /// fixed to enforce handedness. Density-independent.
80    pub principal_axes: [[f64; 3]; 3],
81}
82
83/// Mass properties scaled to a physical density (Golovanov §8.11). The
84/// underlying `FullMassProperties` is a UNIT-density geometric result; here
85/// `mass = density * volume` and every inertia quantity scales linearly with
86/// density (`inertia = density * geometric_inertia`). The centroid and the
87/// principal AXES are density-independent; only the principal MOMENTS and the
88/// mass scale with density.
89#[derive(Clone, Copy, Debug, Serialize)]
90pub struct DensityMassProperties {
91    /// Density used to scale the geometric (unit-density) properties.
92    pub density: f64,
93    /// `mass = density * volume`.
94    pub mass: f64,
95    pub surface_area: f64,
96    pub volume: f64,
97    /// Center of mass (identical to the unit-density centroid).
98    pub centroid: Vec3,
99    /// Centroidal inertia tensor `= density * geometric_inertia`, row-major.
100    pub inertia: [[f64; 3]; 3],
101    /// Principal moments `= density * geometric_principal_moments`, ascending.
102    pub principal_moments: [f64; 3],
103    /// Principal axes (identical to the unit-density axes; density-invariant).
104    pub principal_axes: [[f64; 3]; 3],
105}
106
107impl FullMassProperties {
108    /// Scale the unit-density geometric result to a physical `density`
109    /// (Golovanov §8.11): `mass = density * volume`, `inertia` and the
110    /// principal moments scale by `density`, while the centroid and principal
111    /// axes are unchanged. Panics only on a non-finite density is avoided —
112    /// callers should pass a finite, positive density; a zero density yields a
113    /// massless (all-zero inertia) result, which is well defined.
114    pub fn with_density(&self, density: f64) -> DensityMassProperties {
115        let scale = |matrix: [[f64; 3]; 3]| {
116            let mut out = [[0.0f64; 3]; 3];
117            for row in 0..3 {
118                for column in 0..3 {
119                    out[row][column] = density * matrix[row][column];
120                }
121            }
122            out
123        };
124        DensityMassProperties {
125            density,
126            mass: density * self.volume,
127            surface_area: self.surface_area,
128            volume: self.volume,
129            centroid: self.centroid,
130            inertia: scale(self.inertia),
131            principal_moments: [
132                density * self.principal_moments[0],
133                density * self.principal_moments[1],
134                density * self.principal_moments[2],
135            ],
136            principal_axes: self.principal_axes,
137        }
138    }
139}
140
141
142/// Per-call counters for the trimmed-face integrator, printed to stderr when
143/// `BREP_PROFILE` is set (the switch `boolean.<stage>_ms` and `imprint.*`
144/// use). One line per `solid_mass_properties` / `solid_signed_volume` /
145/// `solid_mass_properties_full` call: which route each trimmed face took,
146/// how many quadrature stations the cells, the boundary triangles and the
147/// chord-arc correction cost, and the wall time of each part. Native only in
148/// practice (no env vars in wasm); when the switch is off every counter is a
149/// thread-local flag test.
150#[path = "mass_properties/profile.rs"]
151mod profile;
152pub(crate) use profile::mass_profile;
153pub use profile::{mass_caller, MassCaller};
154
155/// The content identity of the face set an integrator call reads — the
156/// instrument behind the sign-check pairing, and the key a served value is
157/// checked against.
158#[path = "mass_properties/identity.rs"]
159mod identity;
160
161#[path = "mass_properties/integration.rs"]
162mod integration;
163#[path = "mass_properties/measures.rs"]
164mod measures;
165#[path = "mass_properties/polygons.rs"]
166mod polygons;
167/// Which Gauss–Legendre rule reads one span, and where it is cut: the answer
168/// is the span's own WEIGHTS, because a fixed-order rule is exact for a
169/// polynomial integrand and a rational one is not.
170#[path = "mass_properties/rule.rs"]
171mod rule;
172#[path = "mass_properties/solid_props.rs"]
173mod solid_props;
174#[path = "mass_properties/trimmed.rs"]
175mod trimmed;
176#[path = "mass_properties/winding.rs"]
177mod winding;
178
179use integration::*;
180use measures::*;
181use polygons::*;
182use trimmed::*;
183
184pub use integration::parameter_space_area;
185// The two span helpers `brep/soundness.rs`'s vector-area closure shares with
186// the mass integrals: the surface's knot levels, and a pcurve's spans cut
187// wherever it crosses one. A boundary integral read across a knot line is the
188// same 0.3%-off reading `winding_loops_integral` documents.
189pub(crate) use integration::surface_breaks;
190pub(crate) use winding::split_at_surface_breaks;
191pub use measures::{
192    curve_arc_length, edge_arc_length, face_area, face_boundary_length,
193    face_volume_contribution, solid_edge_length_total,
194};
195pub use solid_props::{solid_mass_properties, solid_mass_properties_full, solid_signed_volume};
196pub(crate) use solid_props::shell_signed_volume;
197pub use polygons::trim_polygons;
198pub use identity::{face_set_identity, FaceSetIdentity};
brep_kernel/props/mass_properties.rs

brep_kernel/props/
mass_properties.rs
