mesh: octree chooses its levels and root size before building

The thinnest wall (measured to a facing wall) and narrowest patch give the cell size the grid
needs; the requested size refined that deep comes first, a root shrunk so one level fewer is
exact second; beyond the levels or cells allowed meshing fails at once naming the wall, levels and
cells. max_depth is a cap (default 4); rebuilds stay within the planned levels; lattice positions
no longer depend on the lattice depth; the report gives root size, levels, wall, patch and cells
per level before and after closure.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/forms.rs

@@ -1246,7 +1246,9 @@ pub const HEX_OCTREE: &[Field] = &[
     SURFACE,
     HEX_SIZE,
     TOLERANCE,
-    int("max_depth", "Refinement levels", 0, 5).help("How many times the octree may refine near the surface.").hint("3"),
+    int("max_depth", "Refinement levels", 0, 5)
+        .help("The most times the octree may refine near thin walls, narrow faces and curves; the levels the part needs are found before meshing.")
+        .hint("4"),
     int("max_elements", "Max elements", 1, 10_000_000).help("Cap on the elements created."),
     int("attempts", "Attempts", 1, 8).help("How many times to retry with adjusted settings.").hint("4"),
     int("max_sweeps", "Optimiser sweeps", 0, 10_000).help("The most smoothing sweeps.").hint("300"),

crates/engine/src/cmd/octree.rs

@@ -15,7 +15,7 @@ use crate::{CommandKind, CommandSpec, EngineError, Result, Session};
 pub const HEX_OCTREE: CommandSpec = CommandSpec {
     id: "mesh.hex.octree",
     label: "Octree Hex Mesh",
-    params: r#"{"body": "Body1" (default: every body of the open design) or "surface": 0 (an imported surface), "size": 2.0 (element size in the interior, mm; default 1/25 of the bounding-box diagonal), "tolerance": 0.05 (chordal tolerance of the tessellation, mm; default 1e-3 of the diagonal), "max_depth": 3 (refinement levels below the size, each a third, 0..=5), "max_elements": 2000000 (1..=10000000; default the session limit), "attempts": 4 (builds, refining where one failed, 1..=8), "max_sweeps": 300 (optimiser sweeps, 0..=10000), and the boundary options of mesh.tet.generate ("weld", "weld_distance", "feature_angle")} — replaces the meshes of the bodies it meshes (as mesh.tet.generate; other bodies keep theirs) with an unstructured all-hex8 mesh of any part: an adaptive 3-refinement grid with conforming transition templates, a core inside the part, two boundary layers that capture every B-rep face boundary and sharp edge, and untangling. Every element is proven valid; boundary element faces are tagged with their B-rep faces (named as in geometry.bodies; by index when a face has no name), so sets by geometry resolve. Reports per body the elements, quality, volume and grid statistics"#,
+    params: r#"{"body": "Body1" (default: every body of the open design) or "surface": 0 (an imported surface), "size": 2.0 (element size in the interior, mm; default 1/25 of the bounding-box diagonal), "tolerance": 0.05 (chordal tolerance of the tessellation, mm; default 1e-3 of the diagonal), "max_depth": 4 (the most refinement levels below the size, each a third, 0..=5; the levels the part's thinnest wall and narrowest face need are found before meshing, and a part that needs more levels or more than max_elements cells fails at once, naming them), "max_elements": 2000000 (1..=10000000; default the session limit), "attempts": 4 (builds, refining where one failed, 1..=8), "max_sweeps": 300 (optimiser sweeps, 0..=10000), and the boundary options of mesh.tet.generate ("weld", "weld_distance", "feature_angle")} — replaces the meshes of the bodies it meshes (as mesh.tet.generate; other bodies keep theirs) with an unstructured all-hex8 mesh of any part: an adaptive 3-refinement grid with conforming transition templates, a core inside the part, two boundary layers that capture every B-rep face boundary and sharp edge, and untangling. Every element is proven valid; boundary element faces are tagged with their B-rep faces (named as in geometry.bodies; by index when a face has no name), so sets by geometry resolve. Reports per body the elements, quality, volume and grid statistics (root cell size, levels, the thinnest wall and narrowest face, cells per level after refinement and after closure)"#,
     form: Some(super::forms::HEX_OCTREE),
     kind: CommandKind::Model,
     requires: &[Requirement::Geometry],
@@ -90,7 +90,7 @@ fn hex_octree(s: &mut Session, p: &Value) -> Result<Value> {
             "quality": {"min_scaled_jacobian": r.min_scaled_jacobian, "mean_scaled_jacobian": r.mean_scaled_jacobian},
             "volume": r.volume,
             "surface_volume": r.surface_volume,
-            "grid": {"cells": r.grid_cells, "core_elements": r.core_elements, "layer_elements": r.layer_elements, "frame": r.frame},
+            "grid": {"cells": r.grid_cells, "root_size": r.root_size, "levels": r.levels, "thinnest_wall": finite(r.thinnest_wall), "narrowest_patch": finite(r.narrowest_patch), "refined_per_level": r.refined_cells, "closed_per_level": r.closed_cells, "core_elements": r.core_elements, "layer_elements": r.layer_elements, "frame": r.frame},
             "features": {"corners": r.corners, "curves": r.curves, "patches": r.patches},
             "attempts": r.attempts,
             "retries": r.retries,
@@ -102,6 +102,11 @@ fn hex_octree(s: &mut Session, p: &Value) -> Result<Value> {
     Ok(cleared.report(s, json!({"bodies": report, "nodes": nodes, "elements": elements})))
 }
 
+/// A measure that may be infinite (no wall, no bounded face) as JSON: `null` when it is.
+fn finite(x: f64) -> Value {
+    if x.is_finite() { json!(x) } else { Value::Null }
+}
+
 #[cfg(test)]
 mod tests {
     use std::sync::Arc;