URDF export for robot simulators (#719) (#942)

A design with components and joints exports as a URDF robot description (file.export to .urdf, the MCP export tool, solidcraft-cli run --out, File > Export URDF...). It writes one binary STL per component in metres, links with mass, centre of mass and inertia from material density, and maps rigid, revolute, slider, cylindrical, pin-slot, planar and ball joints to URDF joints or short chains. Loops, broken joints and loose parts are reported as warnings. Options: mesh_prefix, effort, velocity. Docs in docs/urdf.md.

crates/doc/src/assembly.rs

@@ -124,6 +124,10 @@ fn identity() -> Mat {
     IDENTITY
 }
 
+/// How deep and how many placements [`Document::placements`] walks.
+pub const MAX_PLACEMENT_DEPTH: usize = 64;
+pub const MAX_PLACEMENTS: usize = 100_000;
+
 fn map_plane(m: &Mat, p: &Plane) -> Plane {
     let (o, x, y) = (apply_point(m, p.origin), apply_vector(m, p.x), apply_vector(m, p.y));
     Plane::new(o, x, y).unwrap_or(*p)
@@ -375,13 +379,18 @@ impl Document {
     }
 
     /// Every placement of each component: (component, occurrence path ids, world transform).
+    /// A branch stops past [`MAX_PLACEMENT_DEPTH`] levels, the walk past [`MAX_PLACEMENTS`] placements.
     pub fn placements(&self) -> Vec<(u64, Vec<u64>, Mat)> {
         let mut out = vec![(0, Vec::new(), IDENTITY)];
         let mut stack: Vec<(u64, Vec<u64>, Mat)> = vec![(0, Vec::new(), IDENTITY)];
         while let Some((comp, path, m)) = stack.pop() {
-            if path.len() > 64 || out.len() > 100_000 {
+            if out.len() > MAX_PLACEMENTS {
                 break;
             }
+            // Only this branch stops past the depth limit; the others are still walked.
+            if path.len() > MAX_PLACEMENT_DEPTH {
+                continue;
+            }
             for o in self.occurrences.iter().filter(|o| o.parent == comp) {
                 let mut p = path.clone();
                 p.push(o.id);

crates/doc/src/joints.rs

@@ -17,7 +17,8 @@ use solidcraft_geom::Vec3;
 
 use crate::{DocError, Document, IDENTITY, Mat, ModelState, Result, apply_point, apply_vector, mat_inverse, mat_mul};
 
-const MAX_JOINTS: usize = 10_000;
+/// Joints the solver (and the URDF export) reads at most.
+pub const MAX_JOINTS: usize = 10_000;
 
 /// Where a joint origin sits on a component's geometry (component coordinates).
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]

crates/doc/src/lib.rs

@@ -40,7 +40,10 @@ mod project3d;
 pub use project3d::iso_grid;
 pub mod sheet;
 
-pub use assembly::{IDENTITY, Mat, Occurrence, apply_point, apply_vector, is_identity, map_point_expr, mat_inverse, mat_mul, rigid};
+pub use assembly::{
+    IDENTITY, MAX_PLACEMENT_DEPTH, MAX_PLACEMENTS, Mat, Occurrence, apply_point, apply_vector, is_identity, map_point_expr, mat_inverse, mat_mul,
+    rigid,
+};
 pub use document::*;
 pub use eval::{
     EdgeRef, FeatureResult, Model, ModelBody, ModelState, RevolveExtent, SolvedSketch, ThreadInfo, curve_pick_error, edge_names_for, edge_refs,