solidcraft-smlib: mass properties of any body, by its material regions (fork 311946c)

SMLib's mass properties no longer refuse bodies that are not one manifold
solid: several lumps and lumps touching along edges or points are the sum
over their material regions, and a sheet is its faces' area and centre with
volume 0. Docs of Brep::mass_properties and kernel::measure say so.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017itGh5fpMEousnZ91cYcVt

crates/kernel/src/measure.rs

@@ -48,9 +48,10 @@ pub struct MassMeasure {
 /// dRelativeAccuracy".
 const ACCURACY: f64 = 1e-4;
 
-/// Measure a body. A solid body's volume, area and centre are SMLib's, integrated on its exact
-/// surfaces, and its box is SMLib's exact box; a body SMLib cannot measure is an error. A mesh
-/// body is measured from its triangles, exactly.
+/// Measure a body. A B-rep body's volume, area and centre are SMLib's, integrated on its exact
+/// surfaces over its material regions (a sheet's: its faces' area and their centre, volume 0),
+/// and its box is SMLib's exact box; a body SMLib cannot measure is an error. A mesh body is
+/// measured from its triangles, exactly.
 pub fn measure(b: &Body) -> Result<BodyMeasure> {
     if let Some((pos, tris)) = b.triangle_mesh() {
         // Exact for a mesh body; topology counts are facets, sides and vertices.

crates/smlib/SMLIB_REV

@@ -1 +1 @@
-964474aef3baeaca3a1291182eb912297265b3e9
+311946c25118c9443e33c6dfac16ed1b778156e1

crates/smlib/src/measure.rs

@@ -7,7 +7,7 @@ use crate::{Brep, Result, error, ffi};
 /// finest SMLib allows. Analytic primitives then come out within 2e-7 of their closed forms.
 pub const MEASURE_ACCURACY: f64 = 1e-8;
 
-/// Mass properties of a closed solid at unit density (mm, mm², mm³, mm⁵). For a density ρ the
+/// Mass properties of a body at unit density (mm, mm², mm³, mm⁵). For a density ρ the
 /// mass is ρ·`volume` and the inertia scales by ρ.
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub struct MassProperties {
@@ -33,8 +33,9 @@ impl MassProperties {
 
 impl Brep {
     /// Mass properties at `relative_accuracy` (clamped to [1e-8, 1e-1]; [`MEASURE_ACCURACY`] is
-    /// the finest). A body that is not a closed manifold solid is an error; [`Brep::area`]
-    /// measures those.
+    /// the finest): the sum over the body's material regions, so several lumps, or lumps
+    /// touching along edges or at points, measure too. A body with no material (a sheet, an open
+    /// shell) has volume 0 and no inertia, its faces' area and the centroid of that area.
     pub fn mass_properties(&self, relative_accuracy: f64) -> Result<MassProperties> {
         let m = ffi::measure::mass_properties(&self.0, relative_accuracy).map_err(error)?;
         let [area, volume, cx, cy, cz, ixx, iyy, izz, iyz, izx, ixy] = m;