fix(ribbon): scrollable layer dropdown, stop mouse leak to viewport (#227)

The ribbon layer dropdown grew unbounded so a long layer list ran off the
bottom of the screen with no way to scroll. Cap the panel height and make
the list scrollable; short lists still shrink to fit.

While a dropdown was open, the 3D viewport beneath it kept tracking the
cursor over the panel's empty areas, and the OS cursor vanished there. In
iced 0.14 mouse_area/opaque only capture button presses, never CursorMoved,
so a higher stack layer can't swallow motion — gate it state-side instead:

- ignore viewport motion in on_viewport_move while ribbon.open_dropdown is set
- suppress the crosshair overlay's Hidden cursor (and crosshair draw) so the
  normal OS cursor shows over an open dropdown
- route all ribbon dropdown backdrops through a shared dropdown_backdrop()

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/update/viewport.rs

@@ -482,6 +482,15 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
     }
 
     pub(super) fn on_viewport_move(&mut self, p: Point) -> Task<Message> {
+                // A ribbon dropdown is open over the viewport. Its backdrop
+                // cannot swallow cursor motion — in iced 0.14 mouse_area/opaque
+                // capture only button presses, never CursorMoved — so the move
+                // leaks through the stack to the pane mouse_area beneath and
+                // would track the crosshair over the dropdown's empty areas.
+                // Drop the move here instead. (#227)
+                if self.ribbon.open_dropdown.is_some() {
+                    return Task::none();
+                }
                 let i = self.active_tab;
 
                 // UCS icon grip drag: map the cursor onto the UCS plane and

src/app/view/mod.rs

@@ -401,6 +401,7 @@ impl OpenCADStudio {
                 pane_move_rect,
                 pane_drop_rect,
                 tab.pan_mode,
+                self.ribbon.open_dropdown.is_some(),
             )
         };
 

src/ui/overlay.rs

@@ -189,6 +189,7 @@ pub fn selection_overlay<'a>(
     pane_move_rect: Option<iced::Rectangle>,
     pane_drop_rect: Option<iced::Rectangle>,
     pan_mode: bool,
+    suppressed: bool,
 ) -> Element<'a, Message> {
     canvas(SelectionCanvas {
         selection,
@@ -202,6 +203,7 @@ pub fn selection_overlay<'a>(
         pane_move_rect,
         pane_drop_rect,
         pan_mode,
+        suppressed,
     })
     .width(Length::Fill)
     .height(Length::Fill)
@@ -230,6 +232,10 @@ struct SelectionCanvas {
     /// Interactive PAN mode: the crosshair is hidden and the cursor becomes a
     /// hand so the viewport reads as a draggable surface.
     pan_mode: bool,
+    /// A ribbon dropdown (or similar overlay) is open over the viewport. The
+    /// crosshair is not drawn and the OS cursor is shown normally so the panel
+    /// is usable instead of the cursor vanishing over it. (#227)
+    suppressed: bool,
 }
 
 impl SelectionCanvas {
@@ -259,6 +265,12 @@ impl canvas::Program<Message> for SelectionCanvas {
         bounds: iced::Rectangle,
         cursor: mouse::Cursor,
     ) -> mouse::Interaction {
+        // A dropdown/overlay is open over the viewport — show the normal OS
+        // cursor over the whole canvas instead of hiding it for the crosshair,
+        // so the cursor doesn't vanish while using the panel. (#227)
+        if self.suppressed {
+            return mouse::Interaction::default();
+        }
         // PAN mode owns the whole viewport: an open hand when hovering, a
         // closed hand while dragging.
         if self.pan_mode && cursor.is_over(bounds) {
@@ -826,7 +838,7 @@ impl canvas::Program<Message> for SelectionCanvas {
         // top of it would double up the visual feedback.
         let over_divider = self.divider_under(cursor, bounds);
         // PAN mode replaces the crosshair with a hand cursor.
-        if !over_viewcube && !over_divider && !self.pan_mode {
+        if !over_viewcube && !over_divider && !self.pan_mode && !self.suppressed {
             if let Some(cp) = self.selection.last_move_pos {
                 let color = Color {
                     r: 0.85,

src/ui/ribbon/mod.rs

@@ -64,6 +64,16 @@ pub struct LayerInfo {
     pub locked: bool,
 }
 
+/// Full-screen backdrop for an open ribbon dropdown: closes the dropdown when
+/// the user clicks outside the panel. (Cursor motion leaking to the viewport
+/// beneath is blocked in `on_viewport_move`, not here — iced 0.14's mouse_area
+/// can only capture button presses, never CursorMoved. #227.)
+fn dropdown_backdrop<'a>(positioned: Element<'a, Message>) -> Element<'a, Message> {
+    mouse_area(positioned)
+        .on_press(Message::CloseRibbonDropdown)
+        .into()
+}
+
 impl Ribbon {
     pub fn new() -> Self {
         Self {
@@ -547,11 +557,7 @@ impl Ribbon {
                 .width(Fill)
                 .height(Fill);
 
-            return Some(
-                mouse_area(positioned)
-                    .on_press(Message::CloseRibbonDropdown)
-                    .into(),
-            );
+            return Some(dropdown_backdrop(positioned.into()));
         }
 
         if open_id == LAYER_COMBO_ID {
@@ -677,11 +683,7 @@ impl Ribbon {
             .width(Fill)
             .height(Fill);
 
-        Some(
-            mouse_area(positioned)
-                .on_press(Message::CloseRibbonDropdown)
-                .into(),
-        )
+        Some(dropdown_backdrop(positioned.into()))
     }
 
     fn layer_combo_overlay(&self) -> Option<Element<'_, Message>> {
@@ -774,7 +776,12 @@ impl Ribbon {
             })
             .collect();
 
-        let panel = container(column(rows))
+        // Cap the panel height and make the list scrollable so a long layer
+        // list stays reachable instead of running off the bottom of the
+        // screen (#227). Short lists shrink to fit; longer ones scroll.
+        let row_count = self.layer_infos.len().max(1);
+        let list_h = (row_count as f32 * 26.0).min(420.0);
+        let panel = container(scrollable(column(rows)).height(Length::Fixed(list_h)))
             .style(|_: &Theme| container::Style {
                 background: Some(Background::Color(PANEL_BG)),
                 border: Border {
@@ -800,11 +807,7 @@ impl Ribbon {
             .width(Fill)
             .height(Fill);
 
-        Some(
-            mouse_area(positioned)
-                .on_press(Message::CloseRibbonDropdown)
-                .into(),
-        )
+        Some(dropdown_backdrop(positioned.into()))
     }
 
     /// Floating popup for an annotate-tab style combo (text / dimension /
@@ -927,11 +930,7 @@ impl Ribbon {
             .width(Fill)
             .height(Fill);
 
-        Some(
-            mouse_area(positioned)
-                .on_press(Message::CloseRibbonDropdown)
-                .into(),
-        )
+        Some(dropdown_backdrop(positioned.into()))
     }
 
     fn prop_color_overlay(&self) -> Option<Element<'_, Message>> {
@@ -970,11 +969,7 @@ impl Ribbon {
             .width(Fill)
             .height(Fill);
 
-        Some(
-            mouse_area(positioned)
-                .on_press(Message::CloseRibbonDropdown)
-                .into(),
-        )
+        Some(dropdown_backdrop(positioned.into()))
     }
 
     fn prop_linetype_overlay(&self) -> Option<Element<'_, Message>> {
@@ -1063,11 +1058,7 @@ impl Ribbon {
             .width(Fill)
             .height(Fill);
 
-        Some(
-            mouse_area(positioned)
-                .on_press(Message::CloseRibbonDropdown)
-                .into(),
-        )
+        Some(dropdown_backdrop(positioned.into()))
     }
 
     fn prop_lw_overlay(&self) -> Option<Element<'_, Message>> {
@@ -1143,11 +1134,7 @@ impl Ribbon {
             .width(Fill)
             .height(Fill);
 
-        Some(
-            mouse_area(positioned)
-                .on_press(Message::CloseRibbonDropdown)
-                .into(),
-        )
+        Some(dropdown_backdrop(positioned.into()))
     }
 }