Class-A surfacing 3/3: blend curves, curved-edge fillets, the G2 corner and continuity analysis (#1642)

Thanks @midasdf.

crates/doc/src/document.rs

@@ -563,6 +563,10 @@ pub enum FeatureKind {
         /// What to do when the radius is too large for the geometry around the edges.
         #[serde(default, skip_serializing_if = "FilletFit::is_exact")]
         fit: FilletFit,
+        /// What fills the corners where three blended edges meet: the rolling ball's sphere
+        /// (default) or a G2 patch repeating each blend up to the second order.
+        #[serde(default, skip_serializing_if = "FilletCorner::is_rolling")]
+        corner: FilletCorner,
     },
     Chamfer {
         edges: Vec<Position>,
@@ -1311,6 +1315,10 @@ pub enum FeatureKind {
     /// sketch curves: walls only, no caps.
     SurfaceLoft {
         sections: Vec<SheetSection>,
+        #[serde(default = "loft_plain_continuity", skip_serializing_if = "loft_continuity_is_plain")]
+        continuity: [Continuity; 2],
+        #[serde(default, skip_serializing_if = "loft_crown_is_plain")]
+        crown: [f64; 2],
     },
     /// The faces at `faces` copied out at a signed `distance` along their normals as a new
     /// surface body (0 copies them); `chain` takes each pick's whole smooth chain of faces;
@@ -1491,6 +1499,23 @@ pub enum FeatureKind {
     },
 }
 
+/// What fills the corner where three blended edges meet.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum FilletCorner {
+    /// A piece of the rolling ball's sphere: tangent (G1) to each blend.
+    #[default]
+    Rolling,
+    /// A G2 patch repeating each blend's surface up to the second order (see `corner_g2`).
+    G2,
+}
+
+impl FilletCorner {
+    pub fn is_rolling(&self) -> bool {
+        matches!(self, FilletCorner::Rolling)
+    }
+}
+
 /// How Extend continues a surface past its edges.
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
 #[serde(rename_all = "snake_case")]
@@ -1734,6 +1759,28 @@ pub struct SheetSection {
     pub profiles: Option<ProfileSel>,
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub curves: Vec<String>,
+    /// A section picked as an edge chain of a body instead of a sketch: `edges` are points on the
+    /// chain, and the face the chain bounds is the surface the loft leaves there.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub body: Option<BodyName>,
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub edges: Vec<Position>,
+}
+
+/// A loft's continuity where a design does not say: both ends G0, the loft of old, which only
+/// passes through its sections.
+fn loft_plain_continuity() -> [Continuity; 2] {
+    [Continuity::G0, Continuity::G0]
+}
+
+/// A loft's continuity is plain when it only passes through its sections: both ends G0.
+fn loft_continuity_is_plain(c: &[Continuity; 2]) -> bool {
+    *c == [Continuity::G0, Continuity::G0]
+}
+
+/// A loft's crown is plain when neither end is filled out.
+fn loft_crown_is_plain(c: &[f64; 2]) -> bool {
+    c.iter().all(|v| *v == 0.0)
 }
 
 /// Coil cross-sections.