Joints: cam and follower coupling (joint.cam) (#1734)

Thanks @SychPL.

crates/ui-egui/src/dialogs_coupling.rs

@@ -1,5 +1,5 @@
 //! The Gear, Rack and Pinion and Screw dialogs: two joints coupled by radii or a pitch
-//! (`joint.gear`, `joint.rack_pinion`, `joint.screw`). A radius is typed, or comes from the round
+//! (`joint.gear`, `joint.rack_pinion`, `joint.screw`); the Cam dialog is `dialogs_cam.rs`. A radius is typed, or comes from the round
 //! face picked on the part, and then follows that face when the design changes. Picking a gear's
 //! face also picks the joint it turns on. Play turns the driving joint so the coupling shows its
 //! motion before OK.
@@ -259,21 +259,31 @@ pub fn commands(app: &SolveApp, f: &CouplingForm, inputs: &[SelInput]) -> Result
     Ok(vec![(f.command.to_string(), p)])
 }
 
-/// While animating, the preview turns the driving joint a full turn: its first value that turns
-/// (a planar joint's is its third), the values before it as they are.
+/// While animating, the preview turns the driving joint a full turn.
 pub fn animate(s: &Session, f: &CouplingForm, cmds: &mut Vec<(String, Value)>) {
-    let Some(j) = s.doc.assembly.joints.iter().find(|j| j.id == f.a).filter(|_| f.animate) else { return };
+    if f.animate {
+        turn(s, f.a, f.phase, cmds);
+    }
+}
+
+/// Drive `joint` to `phase` of a full turn: its first value that turns (a planar joint's is its
+/// third), the values before it as they are.
+fn turn(s: &Session, joint: u64, phase: f64, cmds: &mut Vec<(String, Value)>) {
+    let Some(j) = s.doc.assembly.joints.iter().find(|j| j.id == joint) else { return };
     let Some(turn) = (0..j.kind.dofs().len()).find(|i| j.kind.is_angle(*i)) else { return };
     let values: Vec<String> = (0..=turn)
         .map(|i| match j.values.get(i).copied().unwrap_or(0.0) {
-            _ if i == turn => format!("{} deg", f.phase * 360.0),
+            _ if i == turn => format!("{} deg", phase * 360.0),
             v if j.kind.is_angle(i) => format!("{} deg", v.to_degrees()),
             v => format!("{v} mm"),
         })
         .collect();
-    cmds.push(("joint.drive".into(), json!({"joint": f.a, "values": values})));
+    cmds.push(("joint.drive".into(), json!({"joint": joint, "values": values})));
 }
 
+#[path = "dialogs_cam.rs"]
+pub mod cam;
+
 #[cfg(test)]
 #[path = "dialogs_coupling_tests.rs"]
 mod tests;