Add Window::pivot and position combo boxes better (#2303)

* Paint ComboBox icon differently if opening upwards

* Add Area::pivot and Window::pivot

* Add Window::contrain

* ComboBox: pop up above if it doesn't fit below

* Add line to changelog

CHANGELOG.md

@@ -17,8 +17,9 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 * Added `Key::Minus` and `Key::Equals` ([#2239](https://github.com/emilk/egui/pull/2239)).
 * Added `egui::gui_zoom` module with helpers for scaling the whole GUI of an app ([#2239](https://github.com/emilk/egui/pull/2239)).
 * You can now put one interactive widget on top of another, and only one will get interaction at a time ([#2244](https://github.com/emilk/egui/pull/2244)).
-* Add `ui.centered`.
-* Added `Area::constrain` which constrains area to the screen bounds. ([#2270](https://github.com/emilk/egui/pull/2270)).
+* Added `ui.centered`.
+* Added `Area::constrain` and `Window::constrain` which constrains area to the screen bounds. ([#2270](https://github.com/emilk/egui/pull/2270)).
+* Added `Area::pivot` and `Window::pivot` which controls what part of the window to position. ([#2303](https://github.com/emilk/egui/pull/2303)).
 
 ### Changed 🔧
 * Panels always have a separator line, but no stroke on other sides. Their spacing has also changed slightly ([#2261](https://github.com/emilk/egui/pull/2261)).

crates/egui/src/containers/area.rs

@@ -49,6 +49,7 @@ pub struct Area {
     constrain: bool,
     order: Order,
     default_pos: Option<Pos2>,
+    pivot: Align2,
     anchor: Option<(Align2, Vec2)>,
     new_pos: Option<Pos2>,
     drag_bounds: Option<Rect>,
@@ -65,6 +66,7 @@ impl Area {
             order: Order::Middle,
             default_pos: None,
             new_pos: None,
+            pivot: Align2::LEFT_TOP,
             anchor: None,
             drag_bounds: None,
         }
@@ -122,16 +124,28 @@ impl Area {
         self
     }
 
+    /// Positions the window and prevents it from being moved
+    pub fn fixed_pos(mut self, fixed_pos: impl Into<Pos2>) -> Self {
+        self.new_pos = Some(fixed_pos.into());
+        self.movable = false;
+        self
+    }
+
     /// Constrains this area to the screen bounds.
     pub fn constrain(mut self, constrain: bool) -> Self {
         self.constrain = constrain;
         self
     }
 
-    /// Positions the window and prevents it from being moved
-    pub fn fixed_pos(mut self, fixed_pos: impl Into<Pos2>) -> Self {
-        self.new_pos = Some(fixed_pos.into());
-        self.movable = false;
+    /// Where the "root" of the area is.
+    ///
+    /// For instance, if you set this to [`Align2::RIGHT_TOP`]
+    /// then [`Self::fixed_pos`] will set the position of the right-top
+    /// corner of the area.
+    ///
+    /// Default: [`Align2::LEFT_TOP`].
+    pub fn pivot(mut self, pivot: Align2) -> Self {
+        self.pivot = pivot;
         self
     }
 
@@ -208,6 +222,7 @@ impl Area {
             enabled,
             default_pos,
             new_pos,
+            pivot,
             anchor,
             drag_bounds,
             constrain,
@@ -229,9 +244,18 @@ impl Area {
         state.interactable = interactable;
         let mut temporarily_invisible = false;
 
+        if pivot != Align2::LEFT_TOP {
+            if is_new {
+                temporarily_invisible = true; // figure out the size first
+            } else {
+                state.pos.x -= pivot.x().to_factor() * state.size.x;
+                state.pos.y -= pivot.y().to_factor() * state.size.y;
+            }
+        }
+
         if let Some((anchor, offset)) = anchor {
             if is_new {
-                temporarily_invisible = true;
+                temporarily_invisible = true; // figure out the size first
             } else {
                 let screen = ctx.available_rect();
                 state.pos = anchor.align_size_within_rect(state.size, screen).min + offset;

crates/egui/src/containers/combo_box.rs

@@ -1,8 +1,16 @@
-use crate::{style::WidgetVisuals, *};
 use epaint::Shape;
 
+use crate::{style::WidgetVisuals, *};
+
+/// Indicate wether or not a popup will be shown above or below the box.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum AboveOrBelow {
+    Above,
+    Below,
+}
+
 /// A function that paints the [`ComboBox`] icon
-pub type IconPainter = Box<dyn FnOnce(&Ui, Rect, &WidgetVisuals, bool)>;
+pub type IconPainter = Box<dyn FnOnce(&Ui, Rect, &WidgetVisuals, bool, AboveOrBelow)>;
 
 /// A drop-down selection menu with a descriptive label.
 ///
@@ -89,6 +97,7 @@ impl ComboBox {
     ///     rect: egui::Rect,
     ///     visuals: &egui::style::WidgetVisuals,
     ///     _is_open: bool,
+    ///     _above_or_below: egui::AboveOrBelow,
     /// ) {
     ///     let rect = egui::Rect::from_center_size(
     ///         rect.center(),
@@ -107,7 +116,10 @@ impl ComboBox {
     ///     .show_ui(ui, |_ui| {});
     /// # });
     /// ```
-    pub fn icon(mut self, icon_fn: impl FnOnce(&Ui, Rect, &WidgetVisuals, bool) + 'static) -> Self {
+    pub fn icon(
+        mut self,
+        icon_fn: impl FnOnce(&Ui, Rect, &WidgetVisuals, bool, AboveOrBelow) + 'static,
+    ) -> Self {
         self.icon = Some(Box::new(icon_fn));
         self
     }
@@ -213,6 +225,23 @@ fn combo_box_dyn<'c, R>(
     let popup_id = button_id.with("popup");
 
     let is_popup_open = ui.memory().is_popup_open(popup_id);
+
+    let popup_height = ui
+        .ctx()
+        .memory()
+        .areas
+        .get(popup_id)
+        .map_or(100.0, |state| state.size.y);
+
+    let above_or_below =
+        if ui.next_widget_position().y + ui.spacing().interact_size.y + popup_height
+            < ui.ctx().input().screen_rect().bottom()
+        {
+            AboveOrBelow::Below
+        } else {
+            AboveOrBelow::Above
+        };
+
     let button_response = button_frame(ui, button_id, is_popup_open, Sense::click(), |ui| {
         // We don't want to change width when user selects something new
         let full_minimum_width = ui.spacing().slider_width;
@@ -243,9 +272,15 @@ fn combo_box_dyn<'c, R>(
                     icon_rect.expand(visuals.expansion),
                     visuals,
                     is_popup_open,
+                    above_or_below,
                 );
             } else {
-                paint_default_icon(ui.painter(), icon_rect.expand(visuals.expansion), visuals);
+                paint_default_icon(
+                    ui.painter(),
+                    icon_rect.expand(visuals.expansion),
+                    visuals,
+                    above_or_below,
+                );
             }
 
             let text_rect = Align2::LEFT_CENTER.align_size_within_rect(galley.size(), rect);
@@ -256,12 +291,18 @@ fn combo_box_dyn<'c, R>(
     if button_response.clicked() {
         ui.memory().toggle_popup(popup_id);
     }
-    let inner = crate::popup::popup_below_widget(ui, popup_id, &button_response, |ui| {
-        ScrollArea::vertical()
-            .max_height(ui.spacing().combo_height)
-            .show(ui, menu_contents)
-            .inner
-    });
+    let inner = crate::popup::popup_above_or_below_widget(
+        ui,
+        popup_id,
+        &button_response,
+        above_or_below,
+        |ui| {
+            ScrollArea::vertical()
+                .max_height(ui.spacing().combo_height)
+                .show(ui, menu_contents)
+                .inner
+        },
+    );
 
     InnerResponse {
         inner,
@@ -316,13 +357,31 @@ fn button_frame(
     response
 }
 
-fn paint_default_icon(painter: &Painter, rect: Rect, visuals: &WidgetVisuals) {
+fn paint_default_icon(
+    painter: &Painter,
+    rect: Rect,
+    visuals: &WidgetVisuals,
+    above_or_below: AboveOrBelow,
+) {
     let rect = Rect::from_center_size(
         rect.center(),
         vec2(rect.width() * 0.7, rect.height() * 0.45),
     );
-    painter.add(Shape::closed_line(
-        vec![rect.left_top(), rect.right_top(), rect.center_bottom()],
-        visuals.fg_stroke,
-    ));
+
+    match above_or_below {
+        AboveOrBelow::Above => {
+            // Upward pointing triangle
+            painter.add(Shape::closed_line(
+                vec![rect.left_bottom(), rect.right_bottom(), rect.center_top()],
+                visuals.fg_stroke,
+            ));
+        }
+        AboveOrBelow::Below => {
+            // Downward pointing triangle
+            painter.add(Shape::closed_line(
+                vec![rect.left_top(), rect.right_top(), rect.center_bottom()],
+                visuals.fg_stroke,
+            ));
+        }
+    }
 }

crates/egui/src/containers/popup.rs

@@ -294,7 +294,23 @@ pub fn was_tooltip_open_last_frame(ctx: &Context, tooltip_id: Id) -> bool {
     false
 }
 
-/// Shows a popup below another widget.
+/// Helper for [`popup_above_or_below_widget`].
+pub fn popup_below_widget<R>(
+    ui: &Ui,
+    popup_id: Id,
+    widget_response: &Response,
+    add_contents: impl FnOnce(&mut Ui) -> R,
+) -> Option<R> {
+    popup_above_or_below_widget(
+        ui,
+        popup_id,
+        widget_response,
+        AboveOrBelow::Below,
+        add_contents,
+    )
+}
+
+/// Shows a popup above or below another widget.
 ///
 /// Useful for drop-down menus (combo boxes) or suggestion menus under text fields.
 ///
@@ -309,24 +325,32 @@ pub fn was_tooltip_open_last_frame(ctx: &Context, tooltip_id: Id) -> bool {
 /// if response.clicked() {
 ///     ui.memory().toggle_popup(popup_id);
 /// }
-/// egui::popup::popup_below_widget(ui, popup_id, &response, |ui| {
+/// let below = egui::AboveOrBelow::Below;
+/// egui::popup::popup_above_or_below_widget(ui, popup_id, &response, below, |ui| {
 ///     ui.set_min_width(200.0); // if you want to control the size
 ///     ui.label("Some more info, or things you can select:");
 ///     ui.label("…");
 /// });
 /// # });
 /// ```
-pub fn popup_below_widget<R>(
+pub fn popup_above_or_below_widget<R>(
     ui: &Ui,
     popup_id: Id,
     widget_response: &Response,
+    above_or_below: AboveOrBelow,
     add_contents: impl FnOnce(&mut Ui) -> R,
 ) -> Option<R> {
     if ui.memory().is_popup_open(popup_id) {
+        let (pos, pivot) = match above_or_below {
+            AboveOrBelow::Above => (widget_response.rect.left_top(), Align2::LEFT_BOTTOM),
+            AboveOrBelow::Below => (widget_response.rect.left_bottom(), Align2::LEFT_TOP),
+        };
+
         let inner = Area::new(popup_id)
             .order(Order::Foreground)
             .constrain(true)
-            .fixed_pos(widget_response.rect.left_bottom())
+            .fixed_pos(pos)
+            .pivot(pivot)
             .show(ui.ctx(), |ui| {
                 // Note: we use a separate clip-rect for this area, so the popup can be outside the parent.
                 // See https://github.com/emilk/egui/issues/825

crates/egui/src/containers/window.rs

@@ -122,6 +122,30 @@ impl<'open> Window<'open> {
         self
     }
 
+    /// Sets the window position and prevents it from being dragged around.
+    pub fn fixed_pos(mut self, pos: impl Into<Pos2>) -> Self {
+        self.area = self.area.fixed_pos(pos);
+        self
+    }
+
+    /// Constrains this window to the screen bounds.
+    pub fn constrain(mut self, constrain: bool) -> Self {
+        self.area = self.area.constrain(constrain);
+        self
+    }
+
+    /// Where the "root" of the window is.
+    ///
+    /// For instance, if you set this to [`Align2::RIGHT_TOP`]
+    /// then [`Self::fixed_pos`] will set the position of the right-top
+    /// corner of the window.
+    ///
+    /// Default: [`Align2::LEFT_TOP`].
+    pub fn pivot(mut self, pivot: Align2) -> Self {
+        self.area = self.area.pivot(pivot);
+        self
+    }
+
     /// Set anchor and distance.
     ///
     /// An anchor of `Align2::RIGHT_TOP` means "put the right-top corner of the window
@@ -156,23 +180,17 @@ impl<'open> Window<'open> {
         self
     }
 
-    /// Set initial position and size of the window.
-    pub fn default_rect(self, rect: Rect) -> Self {
-        self.default_pos(rect.min).default_size(rect.size())
-    }
-
-    /// Sets the window position and prevents it from being dragged around.
-    pub fn fixed_pos(mut self, pos: impl Into<Pos2>) -> Self {
-        self.area = self.area.fixed_pos(pos);
-        self
-    }
-
     /// Sets the window size and prevents it from being resized by dragging its edges.
     pub fn fixed_size(mut self, size: impl Into<Vec2>) -> Self {
         self.resize = self.resize.fixed_size(size);
         self
     }
 
+    /// Set initial position and size of the window.
+    pub fn default_rect(self, rect: Rect) -> Self {
+        self.default_pos(rect.min).default_size(rect.size())
+    }
+
     /// Sets the window pos and size and prevents it from being moved and resized by dragging its edges.
     pub fn fixed_rect(self, rect: Rect) -> Self {
         self.fixed_pos(rect.min).fixed_size(rect.size())