Add Group container

crates/egui/src/containers/group.rs

@@ -0,0 +1,78 @@
+use emath::NumExt;
+use crate::{Align2, Id, Rect, Ui, UiBuilder, Vec2};
+
+pub struct Group {
+    id: Id,
+    rect: Option<Rect>,
+    size: Option<Vec2>,
+    align2: Align2,
+}
+
+impl Group {
+    pub fn new(id: impl Into<Id>) -> Self {
+        Self {
+            id: id.into(),
+            rect: None,
+            size: None,
+            align2: Align2::CENTER_CENTER,
+        }
+    }
+
+    pub fn align2(mut self, align2: Align2) -> Self {
+        self.align2 = align2;
+        self
+    }
+
+    pub fn rect(mut self, rect: Rect) -> Self {
+        self.rect = Some(rect);
+        self
+    }
+
+    pub fn ui<T>(self, ui: &mut Ui, content: impl FnOnce(&mut Ui) -> T) -> T {
+        let id = ui.id().with(self.id);
+        let data_id = id.with("group");
+
+        let rect = if let Some(rect) = self.rect {
+            rect
+        } else if let Some(size) = self.size {
+            let pos = ui.next_widget_position();
+            Rect::from_min_size(pos, size)
+        } else {
+            ui.available_rect_before_wrap()
+        };
+
+        let last_size = ui.ctx().data(|mem| mem.get_temp(data_id));
+
+        let mut content_rect = if let Some(size) = last_size {
+            let left_top = self.align2.align_size_within_rect(size, rect).left_top();
+            Rect::from_min_size(left_top, rect.size())
+        } else {
+            rect
+        };
+
+        // Clamp the content_rect so it doesn't exceed the top left corner
+        let offset = (rect.min - content_rect.min).at_least(Vec2::ZERO);
+        content_rect = content_rect.translate(offset);
+
+        let mut builder = UiBuilder::new().id_salt(id);
+
+        if last_size.is_none() {
+            builder = builder.invisible();
+        }
+
+        let response = ui.scope_builder(builder.max_rect(content_rect), content);
+
+        let size = response.response.rect.size();
+
+        if last_size != Some(size) {
+            ui.ctx().request_discard("Group size changed");
+            ui.ctx().request_repaint();
+        }
+
+        ui.ctx().data_mut(|mem| {
+            mem.insert_temp(data_id, size);
+        });
+
+        response.inner
+    }
+}

crates/egui/src/containers/mod.rs

@@ -18,7 +18,9 @@ pub mod scroll_area;
 mod sides;
 mod tooltip;
 pub(crate) mod window;
+mod group;
 
+pub use group::Group;
 pub use {
     area::{Area, AreaState},
     close_tag::ClosableTag,

crates/egui_demo_lib/src/demo/demo_app_windows.rs

@@ -80,6 +80,7 @@ impl Default for DemoGroups {
                 Box::<super::extra_viewport::ExtraViewport>::default(),
                 Box::<super::font_book::FontBook>::default(),
                 Box::<super::frame_demo::FrameDemo>::default(),
+                Box::<super::group_demo::GroupDemo>::default(),
                 Box::<super::highlighting::Highlighting>::default(),
                 Box::<super::interactive_container::InteractiveContainerDemo>::default(),
                 Box::<super::MiscDemoWindow>::default(),

crates/egui_demo_lib/src/demo/group_demo.rs

@@ -0,0 +1,76 @@
+use egui::{Align, Align2, Group, ScrollArea};
+
+#[derive(PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "serde", serde(default))]
+pub struct GroupDemo {
+    align_x: Align,
+    align_y: Align,
+}
+
+impl Default for GroupDemo {
+    fn default() -> Self {
+        Self {
+            align_x: Align::Center,
+            align_y: Align::Center,
+        }
+    }
+}
+
+impl crate::Demo for GroupDemo {
+    fn name(&self) -> &'static str {
+        "Group"
+    }
+
+    fn show(&mut self, ui: &mut egui::Ui, open: &mut bool) {
+        egui::Window::new(self.name())
+            .open(open)
+            .default_width(300.0)
+            .default_height(300.0)
+            .resizable(true)
+            .constrain_to(ui.available_rect_before_wrap())
+            .show(ui, |ui| {
+                use crate::View as _;
+                self.ui(ui);
+            });
+    }
+}
+
+impl crate::View for GroupDemo {
+    fn ui(&mut self, ui: &mut egui::Ui) {
+        ui.vertical_centered(|ui| {
+            ui.add(crate::egui_github_link_file!());
+        });
+
+        ui.horizontal(|ui| {
+            ui.label("Horizontal:");
+            ui.selectable_value(&mut self.align_x, Align::Min, "Left");
+            ui.selectable_value(&mut self.align_x, Align::Center, "Center");
+            ui.selectable_value(&mut self.align_x, Align::Max, "Right");
+        });
+
+        ui.horizontal(|ui| {
+            ui.label("Vertical:");
+            ui.selectable_value(&mut self.align_y, Align::Min, "Top");
+            ui.selectable_value(&mut self.align_y, Align::Center, "Center");
+            ui.selectable_value(&mut self.align_y, Align::Max, "Bottom");
+        });
+
+        ui.separator();
+
+        let align2 = Align2([self.align_x, self.align_y]);
+
+
+        Group::new("demo_group").align2(align2).ui(ui, |ui| {
+            ui.label("Hello!");
+            let _ = ui.button("A button");
+            ui.label("More text");
+            ScrollArea::vertical().max_height(50.0).show(ui, |ui| {
+                for _ in 0..100 {
+                    ui.label("Even more text");
+                }
+            });
+        });
+        ui.set_height(ui.available_height());
+    }
+}

crates/egui_demo_lib/src/demo/mod.rs

@@ -13,6 +13,7 @@ pub mod drag_and_drop;
 pub mod extra_viewport;
 pub mod font_book;
 pub mod frame_demo;
+pub mod group_demo;
 pub mod highlighting;
 pub mod interactive_container;
 pub mod misc_demo_window;