implement panels (Adanos020#164) against 0.12 with sensible drag/drop…

… behavior

src/widgets/dock_area/drag_and_drop.rs

@@ -138,7 +138,7 @@ enum LockState {
  /// Lock remains locked, but can be unlocked.
  SoftLock,
 
- /// Lock is locked forever. 
+ /// Lock is locked forever.
  HardLock,
 }
 
@@ -162,6 +162,7 @@ impl DragDropState {
  ui: &Ui,
  style: &Style,
  allowed_splits: AllowedSplits,
+ insert_allowed: bool,
  windows_allowed: bool,
  window_bounds: Rect,
  ) -> Option<TabDestination> {
@@ -188,7 +189,7 @@ impl DragDropState {
  let center = rect.center();
  let rect = Rect::from_center_size(center, Vec2::splat(shortest_side));
 
- if button_ui(rect, ui, &mut hovering_buttons, pointer, style, None) {
+ if insert_allowed && button_ui(rect, ui, &mut hovering_buttons, pointer, style, None) {
  match self.hover.dst {
  TreeComponent::Node(surface, node) => {
  destination = Some(TabDestination::Node(surface, node, TabInsert::Append))
@@ -243,6 +244,7 @@ impl DragDropState {
  ui: &Ui,
  style: &Style,
  allowed_splits: AllowedSplits,
+ insert_allowed: bool,
  windows_allowed: bool,
  window_bounds: Rect,
  ) -> Option<TabDestination> {
@@ -287,10 +289,10 @@ impl DragDropState {
  );
 
  // Find out what kind of tab insertion (if any) should be used to move this widget.
- if center_drop_rect.contains(a_pos) {
+ if insert_allowed && center_drop_rect.contains(a_pos) {
  (Some(TabInsert::Append), Rect::EVERYTHING)
  } else if window_drop_rect.contains(a_pos) {
- match windows_allowed {
+ match windows_allowed || !insert_allowed {
  true => (None, Rect::NOTHING),
  false => (Some(TabInsert::Append), Rect::EVERYTHING),
  }

src/widgets/dock_area/show/leaf.rs

@@ -27,6 +27,9 @@ impl<'tree, Tab> DockArea<'tree, Tab> {
  fade_style: Option<(&Style, f32)>,
  ) {
  assert!(self.dock_state[surface_index][node_index].is_leaf());
+ let hide_tab_bar = self.dock_state[surface_index][node_index]
+ .iter_tabs()
+ .all(|tab| tab_viewer.is_fixed_panel(tab));
 
  let rect = self.dock_state[surface_index][node_index]
  .rect()
@@ -40,13 +43,17 @@ impl<'tree, Tab> DockArea<'tree, Tab> {
  ui.spacing_mut().item_spacing = Vec2::ZERO;
  ui.set_clip_rect(rect);
 
- let tabbar_rect = self.tab_bar(
- ui,
- state,
- (surface_index, node_index),
- tab_viewer,
- fade_style.map(|(style, _)| style),
- );
+ let tabbar_rect = if hide_tab_bar {
+ Rect::ZERO
+ } else {
+ self.tab_bar(
+ ui,
+ state,
+ (surface_index, node_index),
+ tab_viewer,
+ fade_style.map(|(style, _)| style),
+ )
+ };
  self.tab_body(
  ui,
  state,

src/widgets/dock_area/show/mod.rs

@@ -187,6 +187,14 @@ impl<'tree, Tab> DockArea<'tree, Tab> {
  let drag_state = state.dnd.as_mut().unwrap();
  let style = self.style.as_ref().unwrap();
 
+ let dst_is_fixed_panel = match drag_state.hover.dst.node_address() {
+ (dst_surf, Some(dst_node)) => self.dock_state[dst_surf][dst_node]
+ .iter_tabs()
+ .all(|tab| tab_viewer.is_fixed_panel(tab)),
+ _ => false,
+ };
+ let insert_allowed = !dst_is_fixed_panel;
+
  let deserted_node = {
  match (
  drag_state.drag.src.node_address(),
@@ -231,6 +239,7 @@ impl<'tree, Tab> DockArea<'tree, Tab> {
  ui,
  style,
  allowed_splits,
+ insert_allowed,
  allowed_in_window,
  window_bounds,
  )
@@ -239,6 +248,7 @@ impl<'tree, Tab> DockArea<'tree, Tab> {
  ui,
  style,
  allowed_splits,
+ insert_allowed,
  allowed_in_window,
  window_bounds,
  )

src/widgets/tab_viewer.rs

@@ -97,4 +97,12 @@ pub trait TabViewer {
  fn scroll_bars(&self, _tab: &Self::Tab) -> [bool; 2] {
  [true, true]
  }
+
+ /// Returns `true` if the tab can be considered a "fixed panel"
+ ///
+ /// If there is only a single fixed panel in a docking area, no tab bar
+ /// will be shown, and the panel thus can't be dragged/moved.
+ fn is_fixed_panel(&self, _tab: &Self::Tab) -> bool {
+ false
+ }
 }