From 22fffc1793b144fb061ed8e3269e493ab03da77f Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emilernerfeldt@gmail.com>
Date: Fri, 25 Sep 2020 14:43:16 +0200
Subject: [PATCH] [widgets] combo box (drop down menu)

---
 CHANGELOG.md                     |   1 +
 egui/src/containers/combo_box.rs | 124 +++++++++++++++++++++++++++++++
 egui/src/containers/mod.rs       |   5 +-
 egui/src/containers/window.rs    |   3 +-
 egui/src/demos/widgets.rs        |  30 ++++++--
 egui/src/memory.rs               |  28 ++++++-
 egui/src/ui.rs                   |  27 +++++++
 egui/src/widgets/color_picker.rs |  10 +--
 8 files changed, 213 insertions(+), 15 deletions(-)
 create mode 100644 egui/src/containers/combo_box.rs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 035ec83a..c9c92c01 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 * Color picker
 * Unicode characters in labels (limited by [what the default font supports](https://fonts.google.com/specimen/Comfortaa#glyphs))
+* Simple drop-down combo box menu
 
 ## 0.1.4 - 2020-09-08
 
diff --git a/egui/src/containers/combo_box.rs b/egui/src/containers/combo_box.rs
new file mode 100644
index 00000000..92b967b9
--- /dev/null
+++ b/egui/src/containers/combo_box.rs
@@ -0,0 +1,124 @@
+use crate::{paint::PaintCmd, style::WidgetVisuals, *};
+
+pub fn combo_box_with_label(
+    ui: &mut Ui,
+    label: impl Into<Label>,
+    selected: impl Into<Label>,
+    menu_contents: impl FnOnce(&mut Ui),
+) -> Response {
+    let label = label.into();
+    let button_id = ui.make_unique_child_id(label.text());
+
+    ui.horizontal(|ui| {
+        let mut response = combo_box(ui, button_id, selected, menu_contents);
+        response |= ui.add(label);
+        response
+    })
+    .0
+}
+
+pub fn combo_box(
+    ui: &mut Ui,
+    button_id: Id,
+    selected: impl Into<Label>,
+    menu_contents: impl FnOnce(&mut Ui),
+) -> Response {
+    let popup_id = button_id.with("popup");
+    let selected = selected.into();
+
+    let button_active = ui.memory().is_popup_open(popup_id);
+    let button_response = button_frame(ui, button_id, button_active, Sense::click(), |ui| {
+        ui.horizontal(|ui| {
+            // We don't want to change width when user selects something new
+            let full_minimum_width = ui.style().spacing.slider_width;
+            let icon_width = ui.style().spacing.icon_width;
+
+            selected.ui(ui);
+
+            let advance = full_minimum_width - icon_width - ui.child_bounds().width();
+            ui.advance_cursor(advance.at_least(0.0));
+
+            let icon_rect = ui.allocate_space(Vec2::splat(icon_width));
+            let button_rect = ui.rect().expand2(ui.style().spacing.button_padding);
+            let mut response = ui.interact(button_rect, button_id, Sense::click());
+            response.active |= button_active;
+            paint_icon(ui.painter(), icon_rect, ui.style().interact(&response));
+        });
+    });
+    if button_response.clicked {
+        ui.memory().toggle_popup(popup_id);
+    }
+
+    if ui.memory().is_popup_open(popup_id) {
+        Area::new(popup_id)
+            .order(Order::Foreground)
+            .fixed_pos(button_response.rect.left_bottom())
+            .show(ui.ctx(), |ui| {
+                let frame = Frame::popup(ui.style());
+                let frame_margin = frame.margin;
+                frame.show(ui, |ui| {
+                    ui.set_min_width(button_response.rect.width() - 2.0 * frame_margin.x);
+                    ui.set_layout(Layout::justified(Direction::Vertical));
+                    menu_contents(ui);
+                })
+            });
+
+        if ui.input().key_pressed(Key::Escape) || ui.input().mouse.click && !button_response.clicked
+        {
+            ui.memory().close_popup();
+        }
+    }
+
+    button_response
+}
+
+fn button_frame(
+    ui: &mut Ui,
+    id: Id,
+    button_active: bool,
+    sense: Sense,
+    add_contents: impl FnOnce(&mut Ui),
+) -> Response {
+    let margin = ui.style().spacing.button_padding;
+    let outer_rect_bounds = ui.available();
+    let inner_rect = outer_rect_bounds.shrink2(margin);
+    let where_to_put_background = ui.painter().add(PaintCmd::Noop);
+    let mut content_ui = ui.child_ui(inner_rect);
+    add_contents(&mut content_ui);
+
+    let outer_rect = Rect::from_min_max(
+        outer_rect_bounds.min,
+        content_ui.child_bounds().max + margin,
+    );
+
+    let mut response = ui.interact(outer_rect, id, sense);
+    response.active |= button_active;
+    let style = ui.style().interact(&response);
+
+    ui.painter().set(
+        where_to_put_background,
+        PaintCmd::Rect {
+            rect: outer_rect,
+            corner_radius: style.corner_radius,
+            fill: style.bg_fill,
+            stroke: style.bg_stroke,
+        },
+    );
+
+    ui.allocate_space(outer_rect.size());
+
+    response
+}
+
+fn paint_icon(painter: &Painter, rect: Rect, visuals: &WidgetVisuals) {
+    let rect = Rect::from_center_size(
+        rect.center(),
+        vec2(rect.width() * 0.7, rect.height() * 0.45),
+    );
+    painter.add(PaintCmd::Path {
+        points: vec![rect.left_top(), rect.right_top(), rect.center_bottom()],
+        closed: true,
+        fill: Default::default(),
+        stroke: visuals.fg_stroke,
+    });
+}
diff --git a/egui/src/containers/mod.rs b/egui/src/containers/mod.rs
index 00d21075..244997b8 100644
--- a/egui/src/containers/mod.rs
+++ b/egui/src/containers/mod.rs
@@ -4,6 +4,7 @@
 
 pub(crate) mod area;
 pub(crate) mod collapsing_header;
+mod combo_box;
 pub(crate) mod frame;
 pub(crate) mod popup;
 pub(crate) mod resize;
@@ -11,6 +12,6 @@ pub(crate) mod scroll_area;
 pub(crate) mod window;
 
 pub use {
-    area::Area, collapsing_header::CollapsingHeader, frame::Frame, popup::*, resize::Resize,
-    scroll_area::ScrollArea, window::Window,
+    area::Area, collapsing_header::CollapsingHeader, combo_box::*, frame::Frame, popup::*,
+    resize::Resize, scroll_area::ScrollArea, window::Window,
 };
diff --git a/egui/src/containers/window.rs b/egui/src/containers/window.rs
index 29fab1d9..f9f37e60 100644
--- a/egui/src/containers/window.rs
+++ b/egui/src/containers/window.rs
@@ -608,8 +608,7 @@ fn show_title_bar(
         let button_size = ui.style().spacing.icon_width;
 
         if collapsible {
-            // TODO: make clickable radius larger
-            ui.allocate_space(vec2(0.0, 0.0)); // HACK: will add left spacing
+            ui.advance_cursor(ui.style().spacing.item_spacing.x);
 
             let rect = ui.allocate_space(Vec2::splat(button_size));
             let collapse_button_response = ui.interact(rect, collapsing_id, Sense::click());
diff --git a/egui/src/demos/widgets.rs b/egui/src/demos/widgets.rs
index 1e905f96..5afed5d8 100644
--- a/egui/src/demos/widgets.rs
+++ b/egui/src/demos/widgets.rs
@@ -1,11 +1,25 @@
 use crate::{color::*, *};
 
+#[derive(Debug, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+enum Enum {
+    First,
+    Second,
+    Third,
+}
+
+impl Default for Enum {
+    fn default() -> Self {
+        Enum::First
+    }
+}
+
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "serde", serde(default))]
 pub struct Widgets {
     button_enabled: bool,
     count: usize,
-    radio: usize,
+    radio: Enum,
     slider_value: f32,
     angle: f32,
     color: Srgba,
@@ -18,7 +32,7 @@ impl Default for Widgets {
     fn default() -> Self {
         Self {
             button_enabled: true,
-            radio: 0,
+            radio: Enum::First,
             count: 0,
             slider_value: 3.4,
             angle: TAU / 8.0,
@@ -48,9 +62,15 @@ impl Widgets {
             .tooltip_text("The current font supports only a few non-latin characters and Egui does not currently support right-to-left text.");
 
         ui.horizontal(|ui| {
-            ui.radio_value("First", &mut self.radio, 0);
-            ui.radio_value("Second", &mut self.radio, 1);
-            ui.radio_value("Final", &mut self.radio, 2);
+            ui.radio_value("First", &mut self.radio, Enum::First);
+            ui.radio_value("Second", &mut self.radio, Enum::Second);
+            ui.radio_value("Third", &mut self.radio, Enum::Third);
+        });
+
+        combo_box_with_label(ui, "Combo Box", format!("{:?}", self.radio), |ui| {
+            ui.radio_value("First", &mut self.radio, Enum::First);
+            ui.radio_value("Second", &mut self.radio, Enum::Second);
+            ui.radio_value("Third", &mut self.radio, Enum::Third);
         });
 
         ui.add(Checkbox::new(&mut self.button_enabled, "Button enabled"));
diff --git a/egui/src/memory.rs b/egui/src/memory.rs
index 6f955e4e..1cc170f0 100644
--- a/egui/src/memory.rs
+++ b/egui/src/memory.rs
@@ -45,8 +45,9 @@ pub struct Memory {
     pub(crate) color_cache: Cache<Srgba, Hsva>,
 
     /// Which popup-window is open (if any)?
+    /// Could be a combo box, color picker, menu etc.
     #[cfg_attr(feature = "serde", serde(skip))]
-    pub(crate) popup: Option<Id>,
+    popup: Option<Id>,
 }
 
 /// Say there is a button in a scroll area.
@@ -173,6 +174,31 @@ impl Memory {
     }
 }
 
+/// ## Popups
+/// Popups are things like combo-boxes, color pickers, menus etc.
+/// Only one can be be open at a time.
+impl Memory {
+    pub fn is_popup_open(&mut self, popup_id: Id) -> bool {
+        self.popup == Some(popup_id)
+    }
+
+    pub fn open_popup(&mut self, popup_id: Id) {
+        self.popup = Some(popup_id);
+    }
+
+    pub fn close_popup(&mut self) {
+        self.popup = None;
+    }
+
+    pub fn toggle_popup(&mut self, popup_id: Id) {
+        if self.is_popup_open(popup_id) {
+            self.close_popup();
+        } else {
+            self.open_popup(popup_id);
+        }
+    }
+}
+
 impl Areas {
     pub(crate) fn count(&self) -> usize {
         self.areas.len()
diff --git a/egui/src/ui.rs b/egui/src/ui.rs
index 87738975..5285d8b6 100644
--- a/egui/src/ui.rs
+++ b/egui/src/ui.rs
@@ -193,6 +193,11 @@ impl Ui {
         Rect::from_min_max(self.top_left(), bottom_right)
     }
 
+    pub fn set_min_width(&mut self, width: f32) {
+        self.child_bounds.max.x = self.child_bounds.max.x.max(self.child_bounds.min.x + width);
+        self.desired_rect.max.x = self.desired_rect.max.x.max(self.desired_rect.min.x + width);
+    }
+
     /// Set the width of the ui.
     /// You won't be able to shrink it beyond its current child bounds.
     pub fn set_desired_width(&mut self, width: f32) {
@@ -357,6 +362,28 @@ impl Ui {
     // ------------------------------------------------------------------------
     // Stuff that moves the cursor, i.e. allocates space in this ui!
 
+    /// Advance the cursor (where the next widget is put) by this many points.
+    /// The direction is dependent on the layout.
+    /// This is useful for creating some extra space between widgets.
+    pub fn advance_cursor(&mut self, amount: f32) {
+        match self.layout.dir() {
+            Direction::Horizontal => {
+                if self.layout.is_reversed() {
+                    self.cursor.x -= amount;
+                } else {
+                    self.cursor.x += amount;
+                }
+            }
+            Direction::Vertical => {
+                if self.layout.is_reversed() {
+                    self.cursor.y -= amount;
+                } else {
+                    self.cursor.y += amount;
+                }
+            }
+        }
+    }
+
     /// Reserve this much space and move the cursor.
     /// Returns where to put the widget.
     ///
diff --git a/egui/src/widgets/color_picker.rs b/egui/src/widgets/color_picker.rs
index 52966b36..af3ff6fd 100644
--- a/egui/src/widgets/color_picker.rs
+++ b/egui/src/widgets/color_picker.rs
@@ -219,15 +219,15 @@ fn color_picker_hsva_2d(ui: &mut Ui, hsva: &mut Hsva) {
 }
 
 pub fn color_edit_button_hsva(ui: &mut Ui, hsva: &mut Hsva) -> Response {
-    let id = ui.make_position_id().with("foo");
+    let pupup_id = ui.make_position_id().with("popup");
     let button_response = color_button(ui, (*hsva).into()).tooltip_text("Click to edit color");
 
     if button_response.clicked {
-        ui.memory().popup = Some(id);
+        ui.memory().toggle_popup(pupup_id);
     }
     // TODO: make it easier to show a temporary popup that closes when you click outside it
-    if ui.memory().popup == Some(id) {
-        let area_response = Area::new(id)
+    if ui.memory().is_popup_open(pupup_id) {
+        let area_response = Area::new(pupup_id)
             .order(Order::Foreground)
             .default_pos(button_response.rect.max)
             .show(ui.ctx(), |ui| {
@@ -239,7 +239,7 @@ pub fn color_edit_button_hsva(ui: &mut Ui, hsva: &mut Hsva) -> Response {
         if !button_response.clicked {
             let clicked_outside = ui.input().mouse.click && !area_response.hovered;
             if clicked_outside || ui.input().key_pressed(Key::Escape) {
-                ui.memory().popup = None;
+                ui.memory().close_popup();
             }
         }
     }