Api redesign with events for displaying.

Fixes: #358

You can open / close windows programmatically to events. See demo about.

The good thing about the new API, is that it won't lock the
borrowchecker (unlike open). It's maybe a good idea to considering open
as deprecated.

crates/egui/src/containers/collapsing_header.rs

@@ -6,7 +6,8 @@ use epaint::Shape;
 #[derive(Clone, Copy, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub(crate) struct InnerState {
-    open: bool,
+    open: bool,   // Expand / collapse
+    hidden: bool, // Show / Hide
 
     /// Height of the region when open. Used for animations
     #[cfg_attr(feature = "serde", serde(default))]
@@ -25,13 +26,6 @@ pub struct CollapsingState {
 }
 
 impl CollapsingState {
-    pub fn load(ctx: &Context, id: Id) -> Option<Self> {
-        ctx.data_mut(|d| {
-            d.get_persisted::<InnerState>(id)
-                .map(|state| Self { id, state })
-        })
-    }
-
     pub fn store(&self, ctx: &Context) {
         ctx.data_mut(|d| d.insert_persisted(self.id, self.state));
     }
@@ -44,11 +38,16 @@ impl CollapsingState {
         self.id
     }
 
-    pub fn load_with_default_open(ctx: &Context, id: Id, default_open: bool) -> Self {
-        Self::load(ctx, id).unwrap_or(CollapsingState {
+    pub fn load(ctx: &Context, id: Id, default_open: bool) -> Self {
+        ctx.data_mut(|d| {
+            d.get_persisted::<InnerState>(id)
+                .map(|state| Self { id, state })
+        })
+        .unwrap_or(CollapsingState {
             id,
             state: InnerState {
                 open: default_open,
+                hidden: false,
                 open_height: None,
             },
         })
@@ -62,11 +61,23 @@ impl CollapsingState {
         self.state.open = open;
     }
 
-    pub fn toggle(&mut self, ui: &Ui) {
+    pub fn toggle_open(&mut self, ui: &Ui) {
         self.state.open = !self.state.open;
         ui.ctx().request_repaint();
     }
 
+    pub fn is_hidden(&self) -> bool {
+        self.state.hidden
+    }
+
+    pub fn toggle_hidden(&mut self) {
+        self.state.hidden = !self.state.hidden;
+    }
+
+    pub fn set_hidden(&mut self, hidden: bool) {
+        self.state.hidden = hidden;
+    }
+
     /// 0 for closed, 1 for open, with tweening
     pub fn openness(&self, ctx: &Context) -> f32 {
         if ctx.memory(|mem| mem.everything_is_visible()) {
@@ -85,7 +96,7 @@ impl CollapsingState {
         let (_id, rect) = ui.allocate_space(button_size);
         let response = ui.interact(rect, self.id, Sense::click());
         if response.clicked() {
-            self.toggle(ui);
+            self.toggle_open(ui);
         }
         let openness = self.openness(ui.ctx());
         paint_default_icon(ui, openness, &response);
@@ -107,7 +118,7 @@ impl CollapsingState {
         let (_id, rect) = ui.allocate_space(size);
         let response = ui.interact(rect, self.id, Sense::click());
         if response.clicked() {
-            self.toggle(ui);
+            self.toggle_open(ui);
         }
 
         let (mut icon_rect, _) = ui.spacing().icon_rectangles(response.rect);
@@ -535,14 +546,15 @@ impl CollapsingHeader {
             header_response.rect.center().y - text.size().y / 2.0,
         );
 
-        let mut state = CollapsingState::load_with_default_open(ui.ctx(), id, default_open);
+        let mut state = CollapsingState::load(ui.ctx(), id, default_open);
+
         if let Some(open) = open {
             if open != state.is_open() {
-                state.toggle(ui);
+                state.toggle_open(ui);
                 header_response.mark_changed();
             }
         } else if header_response.clicked() {
-            state.toggle(ui);
+            state.toggle_open(ui);
             header_response.mark_changed();
         }
 

crates/egui/src/containers/mod.rs

@@ -21,5 +21,5 @@ pub use {
     popup::*,
     resize::Resize,
     scroll_area::ScrollArea,
-    window::Window,
+    window::{DisplayEvent, Window},
 };

crates/egui/src/containers/window.rs

@@ -27,14 +27,33 @@ use super::*;
 #[must_use = "You should call .show()"]
 pub struct Window<'open> {
     title: WidgetText,
-    open: Option<&'open mut bool>,
     area: Area,
     frame: Option<Frame>,
     resize: Resize,
     scroll: ScrollArea,
     collapsible: bool,
     default_open: bool,
     with_title_bar: bool,
+    with_closing_btn: bool,
+    display_event: Option<DisplayEvent>,
+    open: Option<&'open mut bool>,
+}
+
+#[derive(PartialEq, Default, Clone, Copy, Debug)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub enum DisplayEvent {
+    #[default]
+    Expand,
+    Collapse,
+    Hide,
+    ToggleCollapse,
+    ToggleHidden,
+}
+
+impl DisplayEvent {
+    pub fn equals(&self, other: DisplayEvent) -> bool {
+        self == &other
+    }
 }
 
 impl<'open> Window<'open> {
@@ -44,6 +63,7 @@ impl<'open> Window<'open> {
     pub fn new(title: impl Into<WidgetText>) -> Self {
         let title = title.into().fallback_text_style(TextStyle::Heading);
         let area = Area::new(Id::new(title.text())).constrain(true);
+
         Self {
             title,
             open: None,
@@ -55,8 +75,10 @@ impl<'open> Window<'open> {
                 .default_size([340.0, 420.0]), // Default inner size of a window
             scroll: ScrollArea::neither(),
             collapsible: true,
-            default_open: true,
             with_title_bar: true,
+            with_closing_btn: false,
+            default_open: true,
+            display_event: None,
         }
     }
 
@@ -71,8 +93,15 @@ impl<'open> Window<'open> {
     /// * If `*open == false`, the window will not be visible.
     /// * If `*open == true`, the window will have a close button.
     /// * If the close button is pressed, `*open` will be set to `false`.
+    //#[deprecated = "Use display_state and closing_button instead"]
     pub fn open(mut self, open: &'open mut bool) -> Self {
         self.open = Some(open);
+        self.with_closing_btn = true;
+        self
+    }
+
+    pub fn closing_button(mut self, closing_button: bool) -> Self {
+        self.with_closing_btn = closing_button;
         self
     }
 
@@ -205,6 +234,11 @@ impl<'open> Window<'open> {
         self
     }
 
+    pub fn display_mode(mut self, new_event: &mut Option<DisplayEvent>) -> Self {
+        self.display_event = new_event.take();
+        self
+    }
+
     /// Set initial size of the window.
     pub fn default_size(mut self, default_size: impl Into<Vec2>) -> Self {
         self.resize = self.resize.default_size(default_size);
@@ -317,33 +351,58 @@ impl<'open> Window<'open> {
     ) -> Option<InnerResponse<Option<R>>> {
         let Window {
             title,
-            open,
+            mut open,
             area,
             frame,
             resize,
             scroll,
             collapsible,
-            default_open,
             with_title_bar,
+            with_closing_btn,
+            default_open,
+            display_event,
         } = self;
 
         let frame = frame.unwrap_or_else(|| Frame::window(&ctx.style()));
 
-        let is_explicitly_closed = matches!(open, Some(false));
-        let is_open = !is_explicitly_closed || ctx.memory(|mem| mem.everything_is_visible());
+        let area_id = area.id;
+        let mut collapsing = CollapsingState::load(ctx, area_id.with("collapsing"), default_open);
+
+        // Borrow open to not consume it.
+        // This is for backwards compatibility with events
+        fn backwards_compatibility_open(
+            open: &mut Option<&mut bool>,
+            collapsing: &CollapsingState,
+        ) {
+            if let Some(open) = open {
+                **open = !collapsing.is_hidden();
+            }
+        }
+
+        match display_event {
+            Some(DisplayEvent::Hide) => collapsing.set_hidden(true),
+            Some(DisplayEvent::Expand) => collapsing.set_open(true),
+            Some(DisplayEvent::Collapse) => collapsing.set_open(false),
+            Some(DisplayEvent::ToggleHidden) => collapsing.toggle_hidden(),
+            Some(DisplayEvent::ToggleCollapse) => collapsing.set_open(!collapsing.is_open()),
+            None => collapsing.set_hidden(matches!(open, Some(false))),
+        }
+
+        let is_open = !collapsing.is_hidden() || ctx.memory(|mem| mem.everything_is_visible());
         area.show_open_close_animation(ctx, &frame, is_open);
 
+        backwards_compatibility_open(&mut open, &collapsing);
+
         if !is_open {
+            collapsing.store(ctx);
             return None;
         }
 
-        let area_id = area.id;
-        let area_layer_id = area.layer();
         let resize_id = area_id.with("resize");
-        let mut collapsing =
-            CollapsingState::load_with_default_open(ctx, area_id.with("collapsing"), default_open);
+        let area_layer_id = area.layer();
 
         let is_collapsed = with_title_bar && !collapsing.is_open();
+
         let possible = PossibleInteractions::new(&area, &resize, is_collapsed);
 
         let area = area.movable(false); // We move it manually, or the area will move the window when we want to resize it
@@ -388,6 +447,7 @@ impl<'open> Window<'open> {
         } else {
             None
         };
+
         let hover_interaction = resize_hover(ctx, possible, area_layer_id, last_frame_outer_rect);
 
         let mut area_content_ui = area.content_ui(ctx);
@@ -397,12 +457,11 @@ impl<'open> Window<'open> {
             let frame_stroke = frame.stroke;
             let mut frame = frame.begin(&mut area_content_ui);
 
-            let show_close_button = open.is_some();
             let title_bar = if with_title_bar {
                 let title_bar = show_title_bar(
                     &mut frame.content_ui,
                     title,
-                    show_close_button,
+                    with_closing_btn,
                     &mut collapsing,
                     collapsible,
                 );
@@ -438,7 +497,7 @@ impl<'open> Window<'open> {
                     &mut area_content_ui,
                     outer_rect,
                     &content_response,
-                    open,
+                    with_closing_btn,
                     &mut collapsing,
                     collapsible,
                 );
@@ -468,11 +527,13 @@ impl<'open> Window<'open> {
 
         let full_response = area.end(ctx, area_content_ui);
 
-        let inner_response = InnerResponse {
+        // Hide butten could have been pressed
+        backwards_compatibility_open(&mut open, &collapsing);
+
+        Some(InnerResponse {
             inner: content_inner,
             response: full_response,
-        };
-        Some(inner_response)
+        })
     }
 }
 
@@ -907,7 +968,7 @@ impl TitleBar {
         ui: &mut Ui,
         outer_rect: Rect,
         content_response: &Option<Response>,
-        open: Option<&mut bool>,
+        with_closing_btn: bool,
         collapsing: &mut CollapsingState,
         collapsible: bool,
     ) {
@@ -916,11 +977,9 @@ impl TitleBar {
             self.rect.max.x = self.rect.max.x.max(content_response.rect.max.x);
         }
 
-        if let Some(open) = open {
-            // Add close button now that we know our full width:
-            if self.close_button_ui(ui).clicked() {
-                *open = false;
-            }
+        // Add close button now that we know our full width:
+        if with_closing_btn && self.close_button_ui(ui).clicked() {
+            collapsing.toggle_hidden();
         }
 
         let full_top_rect = Rect::from_x_y_ranges(self.rect.x_range(), self.min_rect.y_range());
@@ -950,7 +1009,7 @@ impl TitleBar {
             .double_clicked()
             && collapsible
         {
-            collapsing.toggle(ui);
+            collapsing.toggle_open(ui);
         }
     }
 

crates/egui_demo_lib/src/demo/about.rs

@@ -1,7 +1,11 @@
+use egui::DisplayEvent;
+
 #[derive(Default)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "serde", serde(default))]
-pub struct About {}
+pub struct About {
+    display_event: Option<DisplayEvent>,
+}
 
 impl super::Demo for About {
     fn name(&self) -> &'static str {
@@ -13,13 +17,24 @@ impl super::Demo for About {
             .default_width(320.0)
             .default_height(480.0)
             .open(open)
+            .display_mode(&mut self.display_event)
             .show(ctx, |ui| {
                 use super::View as _;
                 self.ui(ui);
             });
     }
 }
 
+impl About {
+    pub fn toggle_collapse(&mut self) {
+        self.display_event = Some(DisplayEvent::ToggleCollapse);
+    }
+
+    pub fn toggle_hidden(&mut self) {
+        self.display_event = Some(DisplayEvent::ToggleHidden);
+    }
+}
+
 impl super::View for About {
     fn ui(&mut self, ui: &mut egui::Ui) {
         use egui::special_emojis::{OS_APPLE, OS_LINUX, OS_WINDOWS};

crates/egui_demo_lib/src/demo/demo_app_windows.rs

@@ -268,6 +268,12 @@ impl DemoWindows {
         egui::TopBottomPanel::top("menu_bar").show(ctx, |ui| {
             egui::menu::bar(ui, |ui| {
                 file_menu_button(ui);
+                if ui.button("Expand / Collapse event").clicked() {
+                    self.about.toggle_collapse();
+                }
+                if ui.button("Show / hide event").clicked() {
+                    self.about.toggle_hidden();
+                }
             });
         });