Create foldable areas

src/app.rs

@@ -75,10 +75,11 @@ impl GuiSettings for App {
                 }),
             }]));
 
-        gui.label("LayoutOptions:");
-        let mut layout_options = gui.layout_options;
-        layout_options.show_gui(gui);
-        gui.layout_options = layout_options;
+        gui.foldable("LayoutOptions", |gui| {
+            let mut layout_options = gui.layout_options;
+            layout_options.show_gui(gui);
+            gui.layout_options = layout_options;
+        });
     }
 }
 

src/layout.rs

@@ -1,3 +1,5 @@
+use std::collections::HashSet;
+
 use crate::{math::*, types::*};
 
 // ----------------------------------------------------------------------------
@@ -7,6 +9,9 @@ pub struct LayoutOptions {
     // Horizontal and vertical spacing between widgets
     pub item_spacing: Vec2,
 
+    /// Indent foldable regions etc by this much.
+    pub indent: f32,
+
     /// Default width of buttons, sliders etc
     pub width: f32,
 
@@ -24,6 +29,7 @@ impl Default for LayoutOptions {
     fn default() -> Self {
         LayoutOptions {
             item_spacing: Vec2 { x: 8.0, y: 4.0 },
+            indent: 21.0,
             width: 200.0,
             button_height: 24.0,
             checkbox_radio_height: 24.0,
@@ -34,10 +40,13 @@ impl Default for LayoutOptions {
 
 // ----------------------------------------------------------------------------
 
-#[derive(Clone, Copy, Debug, Default)]
+#[derive(Clone, Debug, Default)]
 pub struct State {
     /// The widget being interacted with (e.g. dragged, in case of a slider).
     pub active_id: Option<Id>,
+
+    /// Which foldable regions are open.
+    open_foldables: HashSet<Id>,
 }
 
 // ----------------------------------------------------------------------------
@@ -186,6 +195,57 @@ impl Layout {
         interact
     }
 
+    // ------------------------------------------------------------------------
+    // Areas:
+
+    pub fn foldable<S, F>(&mut self, label: S, add_contents: F) -> InteractInfo
+    where
+        S: Into<String>,
+        F: FnOnce(&mut Layout),
+    {
+        let label: String = label.into();
+        let id = self.get_id(&label);
+
+        let rect = Rect {
+            pos: self.cursor,
+            size: Vec2 {
+                x: self.layout_options.width,
+                y: self.layout_options.button_height,
+            },
+        };
+
+        let interact = self.interactive_rect(id, &rect);
+        self.cursor.y += rect.size.y + self.layout_options.item_spacing.y;
+
+        if interact.clicked {
+            if self.state.open_foldables.contains(&id) {
+                self.state.open_foldables.remove(&id);
+            } else {
+                self.state.open_foldables.insert(id);
+            }
+        }
+        let open = self.state.open_foldables.contains(&id);
+
+        self.commands.push(GuiCmd::FoldableHeader {
+            interact,
+            rect,
+            label,
+            open,
+        });
+
+        if open {
+            // TODO: push/pop id stack
+            let old_x = self.cursor.x;
+            self.cursor.x += self.layout_options.indent;
+            add_contents(self);
+            self.cursor.x = old_x;
+
+            // TODO: paint background?
+        }
+
+        interact
+    }
+
     // ------------------------------------------------------------------------
 
     fn interactive_rect(&mut self, id: Id, rect: &Rect) -> InteractInfo {

src/lib.rs

@@ -52,9 +52,10 @@ pub fn show_gui(raw_input_json: &str) -> String {
     use crate::app::GuiSettings;
     APP.lock().unwrap().show_gui(&mut emgui.layout);
 
-    emgui.layout.label("Style:");
     let mut style = emgui.style.clone();
-    style.show_gui(&mut emgui.layout);
+    emgui.layout.foldable("Style", |gui| {
+        style.show_gui(gui);
+    });
     emgui.style = style;
 
     let commands = emgui.paint();

src/style.rs

@@ -142,6 +142,76 @@ fn translate_cmd(out_commands: &mut Vec<PaintCmd>, style: &Style, cmd: GuiCmd) {
                 out_commands.push(debug_rect(rect));
             }
         }
+        GuiCmd::FoldableHeader {
+            interact,
+            label,
+            open,
+            rect,
+        } => {
+            let fill_color = if interact.active {
+                srgba(136, 136, 136, 255)
+            } else if interact.hovered {
+                srgba(100, 100, 100, 255)
+            } else {
+                srgba(68, 68, 68, 255)
+            };
+
+            let stroke_color = if interact.active {
+                srgba(255, 255, 255, 255)
+            } else if interact.hovered {
+                srgba(255, 255, 255, 200)
+            } else {
+                srgba(255, 255, 255, 170)
+            };
+
+            out_commands.push(PaintCmd::Rect {
+                corner_radius: 3.0,
+                fill_color: Some(fill_color),
+                outline: None,
+                pos: rect.pos,
+                size: rect.size,
+            });
+
+            // TODO: paint a little triangle or arrow or something instead of this
+
+            let box_side = 16.0;
+            let box_rect = Rect::from_center_size(
+                vec2(rect.min().x + box_side * 0.5, rect.center().y),
+                vec2(box_side, box_side),
+            );
+            // Draw a minus:
+            out_commands.push(PaintCmd::Line {
+                points: vec![
+                    vec2(box_rect.min().x, box_rect.center().y),
+                    vec2(box_rect.max().x, box_rect.center().y),
+                ],
+                color: stroke_color,
+                width: style.line_width,
+            });
+            if open {
+                // Draw it as a plus:
+                out_commands.push(PaintCmd::Line {
+                    points: vec![
+                        vec2(box_rect.center().x, box_rect.min().y),
+                        vec2(box_rect.center().x, box_rect.max().y),
+                    ],
+                    color: stroke_color,
+                    width: style.line_width,
+                });
+            }
+
+            out_commands.push(PaintCmd::Text {
+                fill_color: stroke_color,
+                font_name: style.font_name.clone(),
+                font_size: style.font_size,
+                pos: Vec2 {
+                    x: box_rect.max().x + 4.0,
+                    y: rect.center().y - style.font_size / 2.0,
+                },
+                text: label,
+                text_align: TextAlign::Start,
+            });
+        }
         GuiCmd::RadioButton {
             checked,
             interact,

src/types.rs

@@ -102,6 +102,13 @@ pub enum GuiCmd {
         rect: Rect,
         text: String,
     },
+    // The header for a foldable region
+    FoldableHeader {
+        interact: InteractInfo,
+        open: bool,
+        rect: Rect,
+        label: String,
+    },
     RadioButton {
         checked: bool,
         interact: InteractInfo,