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//! Source code example of how to create your own widget.
//! This is meant to be read as a tutorial, hence the plethora of comments.
/// iOS-style toggle switch:
///
/// ``` text
/// _____________
/// / /.....\
/// | |.......|
/// \_______\_____/
/// ```
///
/// ## Example:
/// ``` ignore
/// toggle_ui(ui, &mut my_bool);
/// ```
pub fn toggle_ui(ui: &mut egui::Ui, on: &mut bool) -> egui::Response {
// Widget code can be broken up in four steps:
// 1. Decide a size for the widget
// 2. Allocate space for it
// 3. Handle interactions with the widget (if any)
// 4. Paint the widget
// 1. Deciding widget size:
// You can query the `ui` how much space is available,
// but in this example we have a fixed size widget based on the height of a standard button:
let desired_size = ui.spacing().interact_size.y * egui::vec2(2.0, 1.0);
// 2. Allocating space:
// This is where we get a region of the screen assigned.
// We also tell the Ui to sense clicks in the allocated region.
let (rect, mut response) = ui.allocate_exact_size(desired_size, egui::Sense::click());
// 3. Interact: Time to check for clicks!
if response.clicked() {
*on = !*on;
response.mark_changed(); // report back that the value changed
}
// Attach some meta-data to the response which can be used by screen readers:
response.widget_info(|| {
egui::WidgetInfo::selected(egui::WidgetType::Checkbox, ui.is_enabled(), *on, "")
});
// 4. Paint!
// Make sure we need to paint:
if ui.is_rect_visible(rect) {
// Let's ask for a simple animation from egui.
// egui keeps track of changes in the boolean associated with the id and
// returns an animated value in the 0-1 range for how much "on" we are.
let how_on = ui.ctx().animate_bool_responsive(response.id, *on);
// We will follow the current style by asking
// "how should something that is being interacted with be painted?".
// This will, for instance, give us different colors when the widget is hovered or clicked.
let visuals = ui.style().interact_selectable(&response, *on);
// All coordinates are in absolute screen coordinates so we use `rect` to place the elements.
let rect = rect.expand(visuals.expansion);
let radius = 0.5 * rect.height();
ui.painter().rect(
rect,
radius,
visuals.bg_fill,
visuals.bg_stroke,
egui::StrokeKind::Inside,
);
// Paint the circle, animating it from left to right with `how_on`:
let circle_x = egui::lerp((rect.left() + radius)..=(rect.right() - radius), how_on);
let center = egui::pos2(circle_x, rect.center().y);
ui.painter()
.circle(center, 0.75 * radius, visuals.bg_fill, visuals.fg_stroke);
}
// All done! Return the interaction response so the user can check what happened
// (hovered, clicked, ...) and maybe show a tooltip:
response
}
/// Here is the same code again, but a bit more compact:
#[expect(dead_code)]
fn toggle_ui_compact(ui: &mut egui::Ui, on: &mut bool) -> egui::Response {
let desired_size = ui.spacing().interact_size.y * egui::vec2(2.0, 1.0);
let (rect, mut response) = ui.allocate_exact_size(desired_size, egui::Sense::click());
if response.clicked() {
*on = !*on;
response.mark_changed();
}
response.widget_info(|| {
egui::WidgetInfo::selected(egui::WidgetType::Checkbox, ui.is_enabled(), *on, "")
});
if ui.is_rect_visible(rect) {
let how_on = ui.ctx().animate_bool_responsive(response.id, *on);
let visuals = ui.style().interact_selectable(&response, *on);
let rect = rect.expand(visuals.expansion);
let radius = 0.5 * rect.height();
ui.painter().rect(
rect,
radius,
visuals.bg_fill,
visuals.bg_stroke,
egui::StrokeKind::Inside,
);
let circle_x = egui::lerp((rect.left() + radius)..=(rect.right() - radius), how_on);
let center = egui::pos2(circle_x, rect.center().y);
ui.painter()
.circle(center, 0.75 * radius, visuals.bg_fill, visuals.fg_stroke);
}
response
}
// A wrapper that allows the more idiomatic usage pattern: `ui.add(toggle(&mut my_bool))`
/// iOS-style toggle switch.
///
/// ## Example:
/// ``` ignore
/// ui.add(toggle(&mut my_bool));
/// ```
pub fn toggle(on: &mut bool) -> impl egui::Widget + '_ {
move |ui: &mut egui::Ui| toggle_ui(ui, on)
}
pub fn url_to_file_source_code() -> String {
format!("https://github.com/emilk/egui/blob/main/{}", file!())
}