fix(ui): preserve construction tools and dashed feedback (#600)

Construction (X) keeps the active sketch tool, its picked points and inline values while switching line type, and drawing previews and hover show the same dashed pattern as committed construction and centre lines. Fixes #584 and #581.

Co-authored-by: lillith <35337584+0xlillith@users.noreply.github.com>

crates/ui-egui/src/tools.rs

@@ -451,13 +451,34 @@ pub fn finish(app: &mut SolveApp) {
 
 /// Rubber-band preview of the shape being drawn.
 pub(crate) fn paint_preview_curve(
-    sketch: &solidcraft_engine::sketch::Sketch,
+    mut sketch: solidcraft_engine::sketch::Sketch,
     plane: &solidcraft_engine::geom::Plane,
     painter: &egui::Painter,
     proj: &Proj,
     stroke: Stroke,
+    mode: u8,
 ) {
-    paint_curve(sketch, 0, plane, painter, proj, stroke, &mut solidcraft_engine::render::SamplingBudget::new(4096, 65_536));
+    for curve in &mut sketch.curves {
+        curve.centerline = mode == 2 && matches!(curve.kind, solidcraft_engine::sketch::CurveKind::Line { .. });
+        curve.construction = mode != 0 && !curve.centerline;
+    }
+    paint_curve(&sketch, 0, plane, painter, proj, stroke, &mut solidcraft_engine::render::SamplingBudget::new(4096, 65_536));
+}
+
+pub(crate) fn paint_sketch_path(points: &[solidcraft_engine::geom::Vec3], mode: u8, painter: &egui::Painter, proj: &Proj, stroke: Stroke) {
+    if mode == 0 {
+        let screen: Vec<_> = points.iter().filter_map(|point| proj.to_screen(*point)).collect();
+        if screen.len() >= 2 {
+            painter.add(egui::Shape::line(screen, stroke));
+        }
+        return;
+    }
+    let unit = solidcraft_engine::view::grid_step(proj.cam.half_height()).0;
+    for (a, b) in crate::viewport::sketch_segments(points, mode, unit) {
+        if let (Some(a), Some(b)) = (proj.to_screen(a), proj.to_screen(b)) {
+            painter.line_segment([a, b], stroke);
+        }
+    }
 }
 
 pub(crate) fn paint_curve(
@@ -470,10 +491,8 @@ pub(crate) fn paint_curve(
     budget: &mut solidcraft_engine::render::SamplingBudget,
 ) {
     for part in crate::sketch_display::curve_with_budget(sketch, index, plane, proj, painter.ctx().pixels_per_point(), budget).parts {
-        let screen: Vec<_> = part.into_iter().filter_map(|point| proj.to_screen(point)).collect();
-        if screen.len() >= 2 {
-            painter.add(egui::Shape::line(screen, stroke));
-        }
+        let mode = sketch.curves.get(index).map_or(0, |c| if c.centerline { 2 } else { u8::from(c.construction) });
+        paint_sketch_path(&part, mode, painter, proj, stroke);
     }
 }
 
@@ -589,14 +608,12 @@ pub fn preview(app: &SolveApp, t: &Tool, painter: &egui::Painter, proj: &Proj) {
     let Some((h, _)) = t.hover.clone() else { return };
     let h = crate::sketch_dims::effective(app, t, h);
     if let Some(curve) = preview_curve(t, h, crate::sketch_dims::locked_value(app, t, "Sweep")) {
-        paint_preview_curve(&curve, &ss.plane, painter, proj, stroke);
+        paint_preview_curve(curve, &ss.plane, painter, proj, stroke, crate::sketch_palette::mode(app));
         return;
     }
     let pts: Vec<Vec2> = t.pts.iter().map(|p| p.0).collect();
     let line = |a: Vec2, b: Vec2| {
-        if let (Some(x), Some(y)) = (to(a), to(b)) {
-            painter.line_segment([x, y], stroke);
-        }
+        paint_sketch_path(&[ss.plane.to_world(a), ss.plane.to_world(b)], crate::sketch_palette::mode(app), painter, proj, stroke);
     };
     match (t.cmd, pts.as_slice()) {
         ("sketch.line", [.., last]) => {