Class-A surfacing 1/3: the continuity core, a G3 free-form blend and patch crown (#1249)

The continuity core (kernel bridge: Hermite control rows reproducing a support surface's position, tangent, curvature and change of curvature, G0 to G3), surface.blend between two edge chains (#764), and a crown for fitted patches. Existing patches and fillets are unchanged by default (crown 0 is the plain patch bit for bit). SurfaceBlend and Patch.crown are noted under format 22.

crates/doc/src/eval_surface.rs

@@ -6,9 +6,9 @@ use super::*;
 use crate::{RuledCorners, RuledMode};
 use solidcraft_geom::Seg2;
 
-pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature, st: &mut ModelState) -> Result<()> {
+pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature, st: &mut ModelState, warning: &mut Option<String>) -> Result<()> {
     match &f.kind {
-        FeatureKind::Patch { sketch, profiles, body, edges } => {
+        FeatureKind::Patch { sketch, profiles, body, edges, crown } => {
             let mut made = Vec::new();
             if let Some(sk) = sketch {
                 let ss = st.sketch(*sk).ok_or_else(|| DocError::Unknown(format!("sketch {sk} (it must come earlier in the timeline)")))?;
@@ -20,7 +20,7 @@ pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature,
             if !edges.is_empty() {
                 let i = body_at(st, body, edges)?;
                 let b = st.bodies.get(i).ok_or_else(|| DocError::Invalid("body".into()))?;
-                made.push(kernel::patch_edges(&b.body, edges)?);
+                made.push(kernel::patch_edges_crowned(&b.body, edges, *crown)?);
             }
             if made.is_empty() {
                 return Err(DocError::Invalid("a patch needs a sketch region or a loop of edges".into()));
@@ -107,6 +107,26 @@ pub(super) fn eval(doc: &Document, vals: &BTreeMap<String, Value>, f: &Feature,
             }
             Ok(())
         }
+        FeatureKind::SurfaceBlend { from, to, continuity, bulge, align, stitch } => {
+            let a = st.body(&from.body).ok_or_else(|| DocError::Unknown(format!("body `{}`", from.body)))?.body.clone();
+            let b = st.body(&to.body).ok_or_else(|| DocError::Unknown(format!("body `{}`", to.body)))?.body.clone();
+            if from.edges.is_empty() || to.edges.is_empty() {
+                return Err(DocError::Invalid("a blend needs a chain of edges at each end".into()));
+            }
+            let (made, gap) = kernel::blend_between(&a, &from.edges, &b, &to.edges, *continuity, *bulge, *align, BLEND_STATIONS, *stitch)?;
+            if gap > 1e-9 {
+                *warning = Some(format!("the blend's boundary lies up to {gap:.4} mm from the edges it was built on"));
+            }
+            let name = new_name(st, f, 0);
+            // A stitched blend takes the place of both bodies it joins; otherwise it is a new
+            // surface body of its own.
+            if *stitch {
+                let gone = [from.body.clone(), to.body.clone()];
+                st.bodies.retain(|x| !gone.contains(&x.name));
+            }
+            st.bodies.push(ModelBody::new(name, made, f.id));
+            Ok(())
+        }
         FeatureKind::SurfaceExtrude { sketch, profiles, curves, extent } => {
             let ss = sketch_in_feature_frame(
                 doc,
@@ -329,6 +349,9 @@ fn sheet_chains(ss: &SolvedSketch, profiles: Option<&ProfileSel>, curves: &[Stri
 
 /// Most sketch curves one feature chains.
 const MAX_CHAIN_CURVES: usize = 1000;
+/// Stations a blend samples each of its two boundaries at: enough that the boundary it fits is
+/// within a small part of a thousandth of the chain's length of the edges it was built on.
+const BLEND_STATIONS: usize = 41;
 
 /// The sketch curves `ids` (free-form ones exactly where they can be) grouped into chains of segments that meet end to end, each oriented
 /// to run one way. Curves are joined greedily at their free ends: where three meet, one of them