Thin Extrude: walls of a set thickness along sketch curves (#721) (#991)

Thin Extrude builds walls of a set thickness along sketch curves, open chains and closed loops, with the wall centred, inside, outside or on both sides at two thicknesses. Saved under format 20 (thin on an Extrude); an extrude without thin saves as before. Closes #721.

crates/doc/src/eval.rs

@@ -2551,6 +2551,35 @@ fn centered_extrude(plane: &Plane, region: &Region2, start: f64, end: f64, sketc
         .collect()
 }
 
+/// The regions a thin extrude's wall covers in its sketch.
+pub(crate) fn thin_regions(vals: &BTreeMap<String, Value>, ss: &SolvedSketch, thin: &crate::ThinWall) -> Result<Vec<Region2>> {
+    if thin.curves.is_empty() || thin.curves.len() > 1000 {
+        return Err(DocError::Invalid("a thin extrude needs 1…1000 sketch curves".into()));
+    }
+    let t = val(vals, &thin.thickness, Kind::Length)?;
+    let (inside, outside) = match thin.side {
+        crate::ThinSide::Center => (t / 2.0, t / 2.0),
+        crate::ThinSide::Inside => (t, 0.0),
+        crate::ThinSide::Outside => (0.0, t),
+        crate::ThinSide::TwoSides => {
+            let e = thin.thickness2.as_deref().ok_or_else(|| DocError::Invalid("a two-sided thin wall needs `thickness2`".into()))?;
+            (t, val(vals, e, Kind::Length)?)
+        }
+    };
+    if !(inside >= 0.0 && outside >= 0.0 && inside + outside > 0.0) {
+        return Err(DocError::Invalid("the wall thickness must be positive".into()));
+    }
+    let curves = thin
+        .curves
+        .iter()
+        .map(|id| {
+            let ci = ss.sketch.curve_index(id).ok_or_else(|| DocError::Unknown(format!("curve `{id}` of {}", ss.name)))?;
+            Ok(ss.sketch.exact_segs(ci).unwrap_or_else(|| ss.sketch.segs(ci)))
+        })
+        .collect::<Result<Vec<_>>>()?;
+    solidcraft_sketch::thin_wall_regions(&curves, inside, outside).map_err(|e| DocError::Invalid(format!("thin wall: {e}")))
+}
+
 /// How far apart (mm) profiles must stay for their extruded tools to be cut as one.
 const APART_GAP: f64 = 1e-3;
 
@@ -2564,13 +2593,16 @@ fn feature_tools_with_constructor(
 ) -> Result<Vec<Traced>> {
     let unnamed = |bodies: Vec<Body>| -> Vec<Traced> { bodies.into_iter().map(Traced::unnamed).collect() };
     match &f.kind {
-        FeatureKind::Extrude { sketch, profiles, extent, operation, targets } => {
+        FeatureKind::Extrude { sketch, profiles, extent, operation, targets, thin } => {
             let ss = sketch_in_feature_frame(
                 doc,
                 st.sketch(*sketch).ok_or_else(|| DocError::Unknown(format!("sketch {sketch} (it must come earlier in the timeline)")))?,
                 f.component,
             )?;
-            let regions = solidcraft_sketch::merge_regions(&select_profiles(&ss, profiles)?);
+            let regions = match thin {
+                Some(thin) => thin_regions(vals, &ss, thin)?,
+                None => solidcraft_sketch::merge_regions(&select_profiles(&ss, profiles)?),
+            };
             // From / To Object: where the face or point lies along the normal, measured over the
             // middle of the profiles. The points are in this feature's component frame, so the
             // model is seen from there: a target in another, moved component where it is shown.