ui: Relax Nodes takes picked faces (#471)

Use selection puts the selected design faces in the form as faces, in
place of a sphere; Shift/Ctrl-click picks faces while the form is open,
and every click does once the form lists faces.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/forms.rs

@@ -1409,8 +1409,8 @@ pub const NODE_RELAX: &[Field] = &[
         .help("Instead of a centre: a sphere round this element (radius default twice its longest edge).")
         .hint("none"),
     face_rows("faces", "Faces")
-        .help("Instead of a sphere: every node on these CAD faces and the elements touching them, nodes sliding on the faces. Pick faces in the view, then Use selection.")
-        .hint("pick faces"),
+        .help("Instead of a sphere: every node on these CAD faces and the elements touching them, nodes sliding on the faces. Shift-click faces in the view, then Use selection.")
+        .hint("Shift-click faces"),
     labels("nodes", "Nodes", LabelOf::Node).help("Instead of a sphere: these nodes.").hint("none"),
     labels("elements", "Elements", LabelOf::Element).help("Instead of a sphere: the nodes of these elements.").hint("none"),
     references("bodies", "Bodies", C::Body).help("Only the nodes of these bodies.").hint("every body"),

crates/ui-egui/src/context.rs

@@ -165,6 +165,7 @@ fn form(app: &mut ModelApp, ui: &mut egui::Ui, t: &Tokens) {
                 selection::Target::DatumPoint => "Puts the point on what is selected: a vertex, an edge's midpoint, a face's centre, or the centre of a hole or of several items",
                 selection::Target::Bodies => "The selected bodies (Select: Bodies), or the bodies of the selected faces, become the cells",
                 selection::Target::ExtrudeFaces => "Pick the source face and use it, then pick the target surface and use it",
+                selection::Target::Faces => "The selected design faces (Shift-click to pick, Select: Faces) are relaxed instead of a sphere",
             };
             let button = match target {
                 selection::Target::ExtrudeFaces if selection::extrude_key(&params) == "source" => "Use as source",

crates/ui-egui/src/lib.rs

@@ -1252,6 +1252,16 @@ impl ModelApp {
         self.dialog.as_ref().is_some_and(|d| d.command == "mesh.node.relax")
     }
 
+    /// Whether the open Relax Nodes form relaxes listed faces: clicks in the view then pick faces
+    /// instead of placing a sphere.
+    pub fn relax_by_faces(&self) -> bool {
+        self.dialog
+            .as_ref()
+            .filter(|d| d.command == "mesh.node.relax")
+            .and_then(|d| serde_json::from_str::<Value>(&d.text).ok())
+            .is_some_and(|p| p.get("faces").and_then(Value::as_array).is_some_and(|f| !f.is_empty()))
+    }
+
     /// Put the open Relax Nodes form's sphere at `at` (a click on the mesh); a sphere without a
     /// radius yet gets a twentieth of the mesh's size.
     pub fn relax_place(&mut self, at: Vec3) -> bool {
@@ -1264,8 +1274,9 @@ impl ModelApp {
         let mut params = serde_json::from_str::<Value>(&d.text).ok().filter(Value::is_object).unwrap_or_else(|| json!({}));
         params["center"] = json!([at.x, at.y, at.z]);
         if let Some(o) = params.as_object_mut() {
-            o.remove("around_element");
-            o.remove("nodes");
+            for key in ["around_element", "nodes", "elements", "faces"] {
+                o.remove(key);
+            }
         }
         if params.get("radius").and_then(Value::as_f64).is_none_or(|r| !(r > 0.0)) && size > 0.0 && size.is_finite() {
             params["radius"] = json!(size / 20.0);
@@ -1806,6 +1817,9 @@ impl ModelApp {
             }
             selection::Target::ExtrudeFaces => selection::with_extrude_faces(&params, &self.pick.selection)
                 .ok_or("no face is selected: pick the source face, then the target surface (Select: Faces)")?,
+            selection::Target::Faces => {
+                selection::with_faces(&params, &self.pick.selection).ok_or("no face is selected: pick the faces to relax (Select: Faces)")?
+            }
             selection::Target::Bodies => {
                 let bodies = selection::bodies(&self.pick.selection).ok_or("no geometry is selected: pick cells with Select: Bodies")?;
                 let mut out = params.as_object().cloned().unwrap_or_default();
@@ -2511,6 +2525,33 @@ mod tests {
         assert_ne!(app.session.model.node(n).unwrap().xyz, [2.7, 2.6, 2.5]);
     }
 
+    /// Relax Nodes by face (#471): Use selection puts the picked design faces in the form in
+    /// place of a sphere, clicks then pick faces, and OK relaxes them.
+    #[test]
+    fn relax_nodes_takes_picked_faces() {
+        let mut app = ModelApp::new(Session::default());
+        let dir = std::env::temp_dir().join(format!("fieldcraft-relax-faces-{}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let design = dir.join("plate.solidcraft");
+        std::fs::write(&design, fieldcraft_geometry::sample::plate_design(&fieldcraft_geometry::sample::Plate::default()).unwrap()).unwrap();
+        app.run("geometry.open", json!({"path": design.to_string_lossy()})).unwrap();
+        app.run("mesh.tet.generate", json!({"size": 4.0})).unwrap();
+        let body = app.session.design.as_ref().unwrap().bodies[0].clone();
+        let face = body.faces()[0].name.clone();
+        app.start("mesh.node.relax").unwrap();
+        assert!(app.relax_place(Vec3 { x: 1.0, y: 1.0, z: 1.0 }) && !app.relax_by_faces());
+        let picked = fieldcraft_model::geometry::GeometryRef::face(body.name.clone(), face.clone()).unwrap();
+        app.select([selection::Item::Geometry(picked)], selection::Mode::Replace);
+        app.use_selection_in_dialog().unwrap();
+        let params: Value = serde_json::from_str(&app.dialog.as_ref().unwrap().text).unwrap();
+        assert_eq!(params["faces"], json!([{"body": body.name, "face": face}]), "{params}");
+        assert!(params.get("center").is_none() && params.get("radius").is_none(), "{params}");
+        assert!(app.relax_by_faces() && app.relax_preview().is_some());
+        app.dialog = None;
+        app.run("mesh.node.relax", params).unwrap();
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
     /// Mesh Quality reads as a sentence in the status bar, not as its JSON report.
     #[test]
     fn mesh_quality_reports_in_a_line() {

crates/ui-egui/src/selection.rs

@@ -855,6 +855,9 @@ pub enum Target {
     /// The selected faces as an extrusion's `source` while it has none, then as its
     /// `to_surface`: pick the source face, then the target surface.
     ExtrudeFaces,
+    /// The selected geometry faces as `faces: [{body, face}]`, in place of a sphere or labels
+    /// (the faces Relax Nodes relaxes).
+    Faces,
 }
 
 /// Where command `id`'s form takes the selection, if it does. `params` (the form's current
@@ -867,6 +870,7 @@ pub fn target(id: &str, params: &Value) -> Option<Target> {
         "geometry.datum.point" | "geometry.datum.point.edit" => Some(Target::DatumPoint),
         "mesh.cells" => Some(Target::Bodies),
         "mesh.hex.extrude" => Some(Target::ExtrudeFaces),
+        "mesh.node.relax" => Some(Target::Faces),
         "model.boundary_condition.create" | "model.boundary_condition.edit" => Some(Target::TargetSet),
         "model.section.create" | "model.section.edit" | "model.coupling.create" | "model.coupling.edit" | "interaction.rigid_wall" => {
             Some(Target::Set)
@@ -929,6 +933,28 @@ pub fn with_edges(params: &Value, selection: &Selection) -> Option<Value> {
     Some(Value::Object(out))
 }
 
+/// `params` with the selection's geometry faces as `faces`, and no sphere, nodes or elements
+/// (what Relax Nodes relaxes); `None` when no face is selected.
+pub fn with_faces(params: &Value, selection: &Selection) -> Option<Value> {
+    let faces: Vec<Value> = selection
+        .items()
+        .iter()
+        .filter_map(|i| match i {
+            Item::Geometry(g) if matches!(g.entity, Entity::Face(_)) => Some(json!(g)),
+            _ => None,
+        })
+        .collect();
+    if faces.is_empty() {
+        return None;
+    }
+    let mut out = params.as_object().cloned().unwrap_or_default();
+    for key in ["center", "radius", "around_element", "nodes", "elements"] {
+        out.remove(key);
+    }
+    out.insert("faces".into(), Value::Array(faces));
+    Some(Value::Object(out))
+}
+
 /// The key of an extrusion's form the selected faces go into: `source` while it names no face
 /// (and no `source_set`), then `to_surface`.
 pub fn extrude_key(params: &Value) -> &'static str {
@@ -969,7 +995,7 @@ pub fn with_set(params: &Value, target: Target, set: &str) -> Value {
         Target::Set => {
             out.insert("set".into(), json!(set));
         }
-        Target::Members | Target::Edges | Target::Position | Target::DatumPoint | Target::Bodies | Target::ExtrudeFaces => {}
+        Target::Members | Target::Edges | Target::Position | Target::DatumPoint | Target::Bodies | Target::ExtrudeFaces | Target::Faces => {}
     }
     Value::Object(out)
 }

crates/ui-egui/src/viewport.rs

@@ -47,8 +47,10 @@ pub fn show(app: &mut ModelApp, ui: &mut egui::Ui) {
     if response.clicked()
         && let Some(at) = response.interact_pointer_pos()
     {
-        // With Relax Nodes open a click on the mesh places its sphere (#398).
-        let placed = app.relaxing() && app.surface_point(at).is_some_and(|p| app.relax_place(p));
+        // With Relax Nodes open a plain click on the mesh places its sphere (#398); Shift or
+        // Ctrl picks faces to relax (#471), and so does every click once the form lists faces.
+        let plain = mode(ui.input(|i| i.modifiers)) == Mode::Replace;
+        let placed = app.relaxing() && plain && !app.relax_by_faces() && app.surface_point(at).is_some_and(|p| app.relax_place(p));
         if !placed {
             let _ = app.select_at(at, mode(ui.input(|i| i.modifiers)));
             probe_at(app, at, rect);