Construction axes, points and planes from model geometry (SOLID ▸ CONSTRUCT): axes through a cylinder/cone/torus, perpendicular to a face at a point, through two planes, two points or an edge; points at a vertex, through two edges, three planes, at the centre of a circle/sphere/torus, at an edge and a plane, along a path; midplane, planes through two edges or three points, tangent to a face, along a path. References (doc::construct::GeoRef) keep picked faces and edges by persistent name and resolve on each evaluation (they follow the model); results live in ModelState.construct, in the component's frame; view::construction_axes/points/planes for the viewport; kernel::face_surface for a face's analytic surface

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/kernel/src/surface_kind.rs

@@ -0,0 +1,52 @@
+//! What surface a face lies on (plane, cylinder, cone, sphere, torus), for construction
+//! geometry: axes through round faces, centres of spheres and tori.
+
+use solvecraft_geom::Vec3;
+
+use crate::Body;
+use crate::offset::{Surf, surf_of};
+
+/// A face's analytic surface. Axes are unit vectors.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum FaceSurface {
+    /// Outward unit normal and a point on the plane.
+    Plane {
+        normal: Vec3,
+        point: Vec3,
+    },
+    Cylinder {
+        origin: Vec3,
+        axis: Vec3,
+        radius: f64,
+    },
+    /// Apex, axis pointing into the cone, half-angle (radians).
+    Cone {
+        apex: Vec3,
+        axis: Vec3,
+        half_angle: f64,
+    },
+    Sphere {
+        center: Vec3,
+        radius: f64,
+    },
+    /// Centre of the ring, its axis, the ring (major) and tube (minor) radii.
+    Torus {
+        center: Vec3,
+        axis: Vec3,
+        major: f64,
+        minor: f64,
+    },
+}
+
+/// The surface of face `face` (in face order), if it is one of the analytic kinds.
+pub fn face_surface(b: &Body, face: usize) -> Option<FaceSurface> {
+    let f = b.solid.face_iter().nth(face)?;
+    let tol = (b.size() * 1e-7).max(1e-9) * 100.0;
+    Some(match surf_of(f, tol)? {
+        Surf::Plane { n, d } => FaceSurface::Plane { normal: n, point: n * d },
+        Surf::Cylinder { o, a, r, .. } => FaceSurface::Cylinder { origin: o, axis: a, radius: r },
+        Surf::Cone { v, a, half, .. } => FaceSurface::Cone { apex: v, axis: a, half_angle: half },
+        Surf::Sphere { c, r, .. } => FaceSurface::Sphere { center: c, radius: r },
+        Surf::Torus { o, a, big, h, r, .. } => FaceSurface::Torus { center: o + a * h, axis: a, major: big, minor: r },
+    })
+}