ui: one number or one per axis for conductivity, expansion and point mass

A PerAxis field kind: one value for every direction, or Per axis ticked
for one per axis. Thermal conductivity and expansion and the point mass
use it instead of a JSON box (#449).

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

crates/engine/src/cmd/forms.rs

@@ -186,18 +186,19 @@ const HYPERELASTIC: Field = variants(
 .help("A large-strain rubber model (nonlinear steps), built on the isotropic constants.")
 .hint("large strain in nonlinear steps, from the isotropic constants");
 
+/// The material axes 1, 2, 3 (the global X, Y, Z until material orientations land).
+const AXES_123: &[&str] = &["1", "2", "3"];
+
 const THERMAL: Field = group(
     "thermal",
     "Thermal",
     &[
-        json("conductivity", "Conductivity")
+        per_axis("conductivity", "Conductivity", D::Conductivity, Some(0.0), AXES_123)
-            .help("Thermal conductivity, one value or one per axis. Steel ≈ 50 W/(m·K), i.e. 50 in mm-t-s-N.")
+            .help("Thermal conductivity, one value or one per material axis. Steel ≈ 50 W/(m·K), i.e. 50 in mm-t-s-N."),
-            .hint("k or [k1, k2, k3]"),
         positive("specific_heat", "Specific heat", D::SpecificHeat)
             .help("Heat that raises a unit mass by one degree. Steel ≈ 460 J/(kg·K), 4.6e8 in mm-t-s."),
-        json("expansion", "Expansion")
+        per_axis("expansion", "Expansion", D::Expansion, None, AXES_123)
-            .help("Thermal expansion coefficient, one value or one per axis, in 1/K. Steel ≈ 1.2e-5, aluminium ≈ 2.3e-5.")
+            .help("Thermal expansion coefficient, one value or one per material axis. Steel ≈ 1.2e-5, aluminium ≈ 2.3e-5."),
-            .hint("α or [α1, α2, α3], 1/K"),
         num("reference_temperature", "Reference temperature", D::Temperature).help("The temperature at which there is no thermal strain.").def("0"),
     ],
 )
@@ -371,7 +372,9 @@ pub const COUPLING: &[Field] = &[
 pub const MASS: &[Field] = &[
     NAME,
     TARGET,
-    positive("mass", "Mass", D::Mass).help("A lumped mass at each node of the target.").hint("per node; [mx, my, mz] in JSON"),
+    per_axis("mass", "Mass", D::Mass, Some(0.0), XYZ)
+        .help("A lumped mass at each node of the target: one value, or one per direction X, Y, Z.")
+        .hint("per node"),
     vector("inertia", "Inertia", D::Inertia, &["I11", "I22", "I33", "I12", "I13", "I23"])
         .help("Rotary inertia about the reference point: three moments and three products.")
         .hint("about the node; needs a reference point"),

crates/engine/src/schema.rs

@@ -112,6 +112,13 @@ pub enum Kind {
         dim: Dim,
         min: Option<f64>,
     },
+    /// One number for every direction, or one per axis (`labels`, e.g. the material axes
+    /// 1, 2, 3), each at least `min`.
+    PerAxis {
+        dim: Dim,
+        min: Option<f64>,
+        labels: &'static [&'static str],
+    },
     /// Any JSON: what the schema does not describe.
     Json,
 }
@@ -390,7 +397,11 @@ impl Field {
     /// Its physical dimension, for a number or a vector of numbers.
     pub fn dim(&self) -> Option<Dim> {
         match self.kind {
-            Kind::Number { dim, .. } | Kind::Vector { dim, .. } | Kind::Points { dim, .. } | Kind::NumberOrAuto { dim, .. } => Some(dim),
+            Kind::Number { dim, .. }
+            | Kind::Vector { dim, .. }
+            | Kind::Points { dim, .. }
+            | Kind::NumberOrAuto { dim, .. }
+            | Kind::PerAxis { dim, .. } => Some(dim),
             _ => None,
         }
     }
@@ -509,6 +520,10 @@ pub const fn multi(key: &'static str, label: &'static str, options: &'static [(&
 pub const fn number_or_auto(key: &'static str, label: &'static str, dim: Dim, min: Option<f64>) -> Field {
     field(key, label, Kind::NumberOrAuto { dim, min })
 }
+/// One number at least `min`, or one per axis of `labels`.
+pub const fn per_axis(key: &'static str, label: &'static str, dim: Dim, min: Option<f64>, labels: &'static [&'static str]) -> Field {
+    field(key, label, Kind::PerAxis { dim, min, labels })
+}
 pub const fn json(key: &'static str, label: &'static str) -> Field {
     field(key, label, Kind::Json)
 }
@@ -1045,6 +1060,18 @@ fn value_problem(f: &'static Field, v: &Value, path: &str, out: &mut Vec<Problem
             (_, Some(_)) => Some(ProblemKind::Below(min.unwrap_or(0.0))),
             _ => Some(ProblemKind::Invalid("a number or \"auto\"".into())),
         },
+        Kind::PerAxis { min, labels, .. } => {
+            let values = match v {
+                Value::Array(a) if a.len() == labels.len() => a.iter().map(|x| x.as_f64().filter(|x| x.is_finite())).collect::<Option<Vec<_>>>(),
+                Value::Array(_) => None,
+                _ => v.as_f64().filter(|x| x.is_finite()).map(|x| vec![x]),
+            };
+            match values {
+                Some(xs) if xs.iter().all(|&x| min.is_none_or(|lo| x >= lo)) => None,
+                Some(_) => Some(ProblemKind::Below(min.unwrap_or(0.0))),
+                None => Some(ProblemKind::Invalid(format!("a number, or {} numbers (one per axis)", labels.len()))),
+            }
+        }
         Kind::Rows { fields, max } => match v.as_array() {
             Some(a) if a.len() <= max => {
                 for (i, row) in a.iter().enumerate() {
@@ -1172,6 +1199,18 @@ fn field_schema(f: &Field, depth: usize) -> Value {
             }
             json!({"oneOf": [n, {"const": "auto"}]})
         }
+        Kind::PerAxis { dim, min, labels } => {
+            let mut n = json!({"type": "number"});
+            if let Some(lo) = min {
+                n["minimum"] = json!(lo);
+            }
+            let mut s =
+                json!({"oneOf": [n.clone(), {"type": "array", "items": n, "minItems": labels.len(), "maxItems": labels.len(), "x-labels": labels}]});
+            if dim != Dim::None {
+                s["x-dimension"] = json!(format!("{dim:?}").to_lowercase());
+            }
+            s
+        }
         _ => json!({}),
     };
     s["title"] = json!(f.label);
@@ -1270,6 +1309,19 @@ mod tests {
         assert_eq!(s["properties"]["path"]["items"]["x-columns"], json!(["fraction", "factor"]));
     }
 
+    /// A per-axis field takes one number or one per axis, each at least its minimum.
+    #[test]
+    fn per_axis_takes_one_number_or_one_per_axis() {
+        const F: &[Field] = &[per_axis("k", "K", Dim::Conductivity, Some(0.0), &["1", "2", "3"])];
+        assert!(problems(F, &json!({"k": 50})).is_empty());
+        assert!(problems(F, &json!({"k": [50, 20, 20.5]})).is_empty());
+        for bad in [json!({"k": -1}), json!({"k": [1, 2]}), json!({"k": [1, 2, -3]}), json!({"k": "x"}), json!({"k": [1, 2, "3"]})] {
+            assert_eq!(problems(F, &bad).len(), 1, "{bad}");
+        }
+        let s = json_schema(F);
+        assert_eq!(s["properties"]["k"]["oneOf"][1]["maxItems"], 3);
+    }
+
     #[test]
     fn prefill_switch_and_check() {
         let p = prefill(LOADISH, &json!({}));

crates/ui-egui/src/describe.rs

@@ -189,6 +189,14 @@ fn scalar(f: &Field, v: &Value, units: UnitSystem) -> String {
         Kind::Multi(options) => {
             list(v, |x| options.iter().find(|(o, _)| fieldcraft_engine::schema::multi_value(o) == *x).map(|(_, l)| (*l).to_string()))
         }
+        Kind::PerAxis { .. } => match v {
+            Value::Array(a) => a
+                .iter()
+                .map(|x| x.as_f64().map_or_else(|| crate::context::value_text(x), |x| with_unit(x, unit.as_deref())))
+                .collect::<Vec<_>>()
+                .join(", "),
+            _ => v.as_f64().map_or_else(|| crate::context::value_text(v), |x| with_unit(x, unit.as_deref())),
+        },
         Kind::NumberOrAuto { .. } => match v {
             Value::String(s) => s.clone(),
             _ => v.as_f64().map_or_else(|| crate::context::value_text(v), |x| with_unit(x, unit.as_deref())),

crates/ui-egui/src/form.rs

@@ -333,6 +333,7 @@ impl Form<'_> {
             Kind::Points { columns, max, .. } => self.points(ui, id, value, f, columns, max),
             Kind::Multi(options) => self.multi(ui, value, options),
             Kind::NumberOrAuto { .. } => self.number_or_auto(ui, id, value, f),
+            Kind::PerAxis { labels, .. } => self.per_axis(ui, id, value, f, labels),
             Kind::Unit | Kind::Group(_) | Kind::Variants { .. } | Kind::Rows { .. } => None,
         }
     }
@@ -715,6 +716,39 @@ impl Form<'_> {
         out
     }
 
+    /// One number, or with Per axis ticked one per axis: ticking it copies the number to every
+    /// axis, unticking keeps the first axis's value.
+    fn per_axis(&mut self, ui: &mut Ui, id: Id, value: Option<&Value>, f: &Field, labels: &[&str]) -> Option<Value> {
+        let split = matches!(value, Some(Value::Array(_)));
+        let mut on = split;
+        let mut out = None;
+        ui.vertical(|ui| {
+            if ui.checkbox(&mut on, "Per axis").on_hover_text("A different value along each axis").changed() {
+                out = Some(match (on, value) {
+                    (true, Some(v)) if v.is_number() => Value::Array(vec![v.clone(); labels.len()]),
+                    (true, _) => Value::Null,
+                    (false, Some(Value::Array(a))) => a.first().cloned().unwrap_or(Value::Null),
+                    (false, _) => Value::Null,
+                });
+            }
+            if split {
+                if let Some(v) = self.vector(ui, id.with("axes"), value, f, labels, false, None) {
+                    out = Some(v);
+                }
+            } else {
+                ui.horizontal(|ui| {
+                    let unit = f.unit_label(self.cx.units);
+                    let width = (fill(ui) - fields::unit_width(ui, unit.as_deref())).max(FIELD_MIN);
+                    if let Some(v) = self.number(ui, id, value, f.hint, false, width) {
+                        out = Some(v);
+                    }
+                    fields::unit(ui, &self.style, unit.as_deref());
+                });
+            }
+        });
+        out
+    }
+
     /// A JSON value typed as text: kept while it does not parse.
     /// Empty, it shows `hint` (the expected format) greyed.
     fn json(&mut self, ui: &mut Ui, id: Id, value: Option<&Value>, hint: &str) -> Option<Value> {
@@ -844,7 +878,7 @@ fn caption(component: &str) -> String {
 pub fn has_system_units(fields: &[Field], depth: usize) -> bool {
     depth <= MAX_DEPTH
         && fields.iter().any(|f| match f.kind {
-            Kind::Number { dim, .. } | Kind::Vector { dim, .. } => dim.follows_system(),
+            Kind::Number { dim, .. } | Kind::Vector { dim, .. } | Kind::PerAxis { dim, .. } => dim.follows_system(),
             Kind::Group(inner) | Kind::Rows { fields: inner, .. } | Kind::Either(inner) => has_system_units(inner, depth + 1),
             Kind::Variants { variants, .. } => variants.iter().any(|v| has_system_units(v.fields, depth + 1)),
             _ => false,