Extrude: a symmetric distance is the total thickness (#1260)

A symmetric solid extrude of 10 mm is now 10 mm thick, 5 mm each side of the sketch plane, and switching from One Side to Symmetric keeps the thickness entered. Under format 21 the extent records its convention; designs saved without it keep the per-side reading, so their geometry and parameters don't change. Fixes #1236.

Co-authored-by: Karl-VonRichter <Karl-VonRichter@users.noreply.github.com>

crates/ui-egui/src/canvas.rs

@@ -338,6 +338,16 @@ fn draw(app: &SolveApp, ui: &mut egui::Ui, painter: &egui::Painter, proj: &Proj,
         _ => 1.0,
     };
     let symmetric = to_span.is_none() && matches!(d.kind, Kind::Extrude { direction: 2, .. });
+    let symmetric_scale = if symmetric {
+        d.extra
+            .get("convention")
+            .cloned()
+            .and_then(|v| serde_json::from_value::<solidcraft_engine::doc::ExtrudeConvention>(v).ok())
+            .unwrap_or(solidcraft_engine::doc::ExtrudeConvention::TotalDistance)
+            .symmetric_half_distance(1.0)
+    } else {
+        1.0
+    };
     // Extrudes and moves go either way; radii and thicknesses stay positive.
     let signed = matches!(
         d.kind,
@@ -416,17 +426,19 @@ fn draw(app: &SolveApp, ui: &mut egui::Ui, painter: &egui::Painter, proj: &Proj,
     if let (Some(n), Some(l)) = (dir, len.filter(|_| kind == ValueKind::Length)) {
         let n = n * sign;
         let baseline = to_span.map(f64::abs).unwrap_or(0.0);
-        let mut shown_value = format_len(l + baseline);
+        // Through All already supplies a reach per side; dragging switches to an entered distance.
+        let half = if all_span.is_some() { l } else { l * symmetric_scale };
+        let mut shown_value = format_len(half + baseline);
         let original_shown = shown_value.clone();
-        let dragged = if to_span.is_some() { &mut shown_value } else { &mut *value };
-        if let Some(ts) = drag_arrow(ui, painter, proj, base, bs, n, l + baseline, signed, egui::Id::new("sc_manipulator"), half_height, dragged) {
-            if to_span.is_some()
+        let dragged = if to_span.is_some() || symmetric_scale != 1.0 { &mut shown_value } else { &mut *value };
+        if let Some(ts) = drag_arrow(ui, painter, proj, base, bs, n, half + baseline, signed, egui::Id::new("sc_manipulator"), half_height, dragged) {
+            if (to_span.is_some() || symmetric_scale != 1.0)
                 && shown_value != original_shown
                 && let Ok(v) = app.session.doc.eval(&shown_value, ValueKind::Length)
             {
-                *value = format_len(v - baseline);
+                *value = format_len((v - baseline) / symmetric_scale);
             }
-            if symmetric && let Some(bt) = proj.to_screen(base - n * l) {
+            if symmetric && let Some(bt) = proj.to_screen(base - n * half) {
                 arrow(painter, bs, bt, t.manipulator);
             }
             painter.circle(bs, 3.5, t.manipulator, Stroke::new(1.0, Color32::WHITE));