Sketch: symmetry about the origin point or an origin axis (#1318)

Fixes #1075. sketch.constraint.symmetry takes a centre point (the origin or any sketch point) as well as a line; the Symmetry tool's third pick may be the origin point or the sketch's own X/Y origin axis. Checked on main + this branch: cargo check --workspace, the engine cmd::sketch tests (257) and the UI symmetry pick tests.

crates/ui-egui/src/tools.rs

@@ -16,6 +16,10 @@ mod display_preview_tests;
 #[path = "sketch_neutral_click_tests.rs"]
 mod neutral_click_tests;
 
+#[cfg(test)]
+#[path = "symmetry_pick_tests.rs"]
+mod symmetry_pick_tests;
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum Kind {
     /// Click points; `n` points complete the shape (0 = chain until finished).
@@ -189,8 +193,12 @@ pub fn on_click(app: &mut SolveApp, proj: &Proj, pos: Pos2) {
         }
         Kind::Pick(n) => {
             let hits = pick(app, proj, pos);
+            // Symmetry's third pick may be an origin axis lying along the sketch's own x or y
+            // (#1075); the command names those `x` / `y`.
+            let axis_ok = tool.cmd == "sketch.constraint.symmetry" && tool.picks.len() == 2;
             if let Some(id) = hits.iter().find_map(|h| match h {
                 Hit::SketchPoint { id, .. } | Hit::SketchCurve { id, .. } => Some(id.clone()),
+                Hit::Axis { name } if axis_ok => sketch_axis_of(app, name).map(str::to_string),
                 _ => None,
             }) {
                 tool.picks.push(id);
@@ -455,6 +463,31 @@ pub(crate) fn projection_preselection(selection: &[solidcraft_engine::Sel]) -> O
         .collect()
 }
 
+/// `x` or `y` when the origin axis `name` is the active sketch's own x or y axis: along it, and
+/// through the sketch's origin.
+fn sketch_axis_of(app: &SolveApp, name: &str) -> Option<&'static str> {
+    use solidcraft_engine::geom::Vec3;
+    let dir = match name {
+        "X" => Vec3::X,
+        "Y" => Vec3::Y,
+        "Z" => Vec3::Z,
+        _ => return None,
+    };
+    let st = app.session.world_state();
+    let plane = st.sketch(app.session.active_sketch?)?.plane;
+    let o = plane.origin;
+    if (o - dir * o.dot(dir)).len() > 1e-6 {
+        return None;
+    }
+    if plane.x.dot(dir).abs() > 1.0 - 1e-9 {
+        Some("x")
+    } else if plane.y.dot(dir).abs() > 1.0 - 1e-9 {
+        Some("y")
+    } else {
+        None
+    }
+}
+
 fn run_pick(app: &mut SolveApp, t: &Tool) {
     let k = &t.picks;
     let params = match t.cmd {