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/document.rs

@@ -179,6 +179,51 @@ pub struct Extent {
     pub from: Option<Vec3>,
 }
 
+/// Thin Extrude: a wall of constant thickness along sketch curves instead of the profiles.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct ThinWall {
+    /// The sketch curves the wall follows: open chains and closed loops, joined where they
+    /// meet end to end.
+    pub curves: Vec<String>,
+    /// The wall thickness (expression); with `side: two_sides`, the thickness inside.
+    pub thickness: String,
+    #[serde(default, skip_serializing_if = "ThinSide::is_center")]
+    pub side: ThinSide,
+    /// With `side: two_sides`, the thickness outside (expression).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub thickness2: Option<String>,
+}
+
+/// Where a thin wall lies against its curves. A closed loop's inside is the area it encloses;
+/// an open chain's is the side it bends toward (a straight one's, the left of its first
+/// curve as drawn).
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum ThinSide {
+    /// Half the thickness either side of the curves.
+    #[default]
+    Center,
+    Inside,
+    Outside,
+    /// `thickness` inside and `thickness2` outside.
+    TwoSides,
+}
+
+impl ThinSide {
+    pub fn is_center(&self) -> bool {
+        *self == ThinSide::Center
+    }
+    pub fn parse(s: &str) -> Option<ThinSide> {
+        match s.trim().to_ascii_lowercase().replace([' ', '-'], "_").as_str() {
+            "center" | "centre" | "centered" | "centred" | "symmetric" => Some(ThinSide::Center),
+            "inside" | "side1" | "side_1" => Some(ThinSide::Inside),
+            "outside" | "side2" | "side_2" => Some(ThinSide::Outside),
+            "two_sides" | "both" => Some(ThinSide::TwoSides),
+            _ => None,
+        }
+    }
+}
+
 /// Revolve axis.
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 #[serde(tag = "type", rename_all = "snake_case")]
@@ -365,6 +410,9 @@ pub enum FeatureKind {
         /// Target body names for join/cut/intersect (empty = all bodies).
         #[serde(default, skip_serializing_if = "Vec::is_empty")]
         targets: Vec<String>,
+        /// Thin: a wall along sketch curves instead of the profiles (which are then unused).
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        thin: Option<ThinWall>,
     },
     Revolve {
         sketch: u64,
@@ -1464,6 +1512,8 @@ impl FeatureKind {
     /// The feature's profile selections, each with its sketch.
     pub fn profile_sels_mut(&mut self) -> Vec<(u64, &mut ProfileSel)> {
         match self {
+            // A thin extrude follows curves; its profiles are not used.
+            FeatureKind::Extrude { thin: Some(_), .. } => Vec::new(),
             FeatureKind::Extrude { sketch, profiles, .. }
             | FeatureKind::Revolve { sketch, profiles, .. }
             | FeatureKind::Sweep { sketch, profiles, .. }
@@ -1484,6 +1534,8 @@ impl FeatureKind {
     /// Profile selections and their source sketches without cloning feature data.
     pub fn profile_sels(&self) -> Vec<(u64, &ProfileSel)> {
         match self {
+            // A thin extrude follows curves; its profiles are not used.
+            FeatureKind::Extrude { thin: Some(_), .. } => Vec::new(),
             FeatureKind::Extrude { sketch, profiles, .. }
             | FeatureKind::Revolve { sketch, profiles, .. }
             | FeatureKind::Sweep { sketch, profiles, .. }