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…#3886) This can be useful for creating simple plugins for egui. The state can be stored in the egui data store, or by the user. An example plugin for painting debug text on screen is provided.
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| //! This is an example of how to create a plugin for egui. | ||
| //! | ||
| //! A plugin usually consist of a struct that holds some state, | ||
| //! which is stored using [`Context::data_mut`]. | ||
| //! The plugin registers itself onto a specific [`Context`] | ||
| //! to get callbacks on certain events ([`Context::on_begin_frame`], [`Context::on_end_frame`]). | ||
| use crate::*; | ||
|
|
||
| /// Register this plugin on the given egui context, | ||
| /// so that it will be called every frame. | ||
| /// | ||
| /// This is a built-in plugin in egui, | ||
| /// meaning [`Context`] calls this from its `Default` implementation, | ||
| /// so this i marked as `pub(crate)`. | ||
| pub(crate) fn register(ctx: &Context) { | ||
| ctx.on_end_frame("debug_text", std::sync::Arc::new(State::end_frame)); | ||
| } | ||
|
|
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| /// Print this text next to the cursor at the end of the frame. | ||
| /// | ||
| /// If you call this multiple times, the text will be appended. | ||
| /// | ||
| /// This only works if compiled with `debug_assertions`. | ||
| /// | ||
| /// ``` | ||
| /// # let ctx = &egui::Context::default(); | ||
| /// # let state = true; | ||
| /// egui::debug_text::print(ctx, format!("State: {state:?}")); | ||
| /// ``` | ||
| #[track_caller] | ||
| pub fn print(ctx: &Context, text: impl Into<WidgetText>) { | ||
| if !cfg!(debug_assertions) { | ||
| return; | ||
| } | ||
|
|
||
| let location = std::panic::Location::caller(); | ||
| let location = format!("{}:{}", location.file(), location.line()); | ||
| ctx.data_mut(|data| { | ||
| // We use `Id::NULL` as the id, since we only have one instance of this plugin. | ||
| // We use the `temp` version instead of `persisted` since we don't want to | ||
| // persist state on disk when the egui app is closed. | ||
| let state = data.get_temp_mut_or_default::<State>(Id::NULL); | ||
| state.entries.push(Entry { | ||
| location, | ||
| text: text.into(), | ||
| }); | ||
| }); | ||
| } | ||
|
|
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| #[derive(Clone)] | ||
| struct Entry { | ||
| location: String, | ||
| text: WidgetText, | ||
| } | ||
|
|
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| /// A plugin for easily showing debug-text on-screen. | ||
| /// | ||
| /// This is a built-in plugin in egui. | ||
| #[derive(Clone, Default)] | ||
| struct State { | ||
| // This gets re-filled every frame. | ||
| entries: Vec<Entry>, | ||
| } | ||
|
|
||
| impl State { | ||
| fn end_frame(ctx: &Context) { | ||
| let state = ctx.data_mut(|data| data.remove_temp::<Self>(Id::NULL)); | ||
| if let Some(state) = state { | ||
| state.paint(ctx); | ||
| } | ||
| } | ||
|
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| fn paint(self, ctx: &Context) { | ||
| let Self { entries } = self; | ||
|
|
||
| if entries.is_empty() { | ||
| return; | ||
| } | ||
|
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| // Show debug-text next to the cursor. | ||
| let mut pos = ctx | ||
| .input(|i| i.pointer.latest_pos()) | ||
| .unwrap_or_else(|| ctx.screen_rect().center()) | ||
| + 8.0 * Vec2::Y; | ||
|
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| let painter = ctx.debug_painter(); | ||
| let where_to_put_background = painter.add(Shape::Noop); | ||
|
|
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| let mut bounding_rect = Rect::from_points(&[pos]); | ||
|
|
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| let color = Color32::GRAY; | ||
| let font_id = FontId::new(10.0, FontFamily::Proportional); | ||
|
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| for Entry { location, text } in entries { | ||
| { | ||
| // Paint location to left of `pos`: | ||
| let location_galley = | ||
| ctx.fonts(|f| f.layout(location, font_id.clone(), color, f32::INFINITY)); | ||
| let location_rect = | ||
| Align2::RIGHT_TOP.anchor_size(pos - 4.0 * Vec2::X, location_galley.size()); | ||
| painter.galley(location_rect.min, location_galley, color); | ||
| bounding_rect = bounding_rect.union(location_rect); | ||
| } | ||
|
|
||
| { | ||
| // Paint `text` to right of `pos`: | ||
| let wrap = true; | ||
| let available_width = ctx.screen_rect().max.x - pos.x; | ||
| let galley = text.into_galley_impl( | ||
| ctx, | ||
| &ctx.style(), | ||
| wrap, | ||
| available_width, | ||
| font_id.clone().into(), | ||
| Align::TOP, | ||
| ); | ||
| let rect = Align2::LEFT_TOP.anchor_size(pos, galley.size()); | ||
| painter.galley(rect.min, galley, color); | ||
| bounding_rect = bounding_rect.union(rect); | ||
| } | ||
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| pos.y = bounding_rect.max.y + 4.0; | ||
| } | ||
|
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| painter.set( | ||
| where_to_put_background, | ||
| Shape::rect_filled( | ||
| bounding_rect.expand(4.0), | ||
| 2.0, | ||
| Color32::from_black_alpha(192), | ||
| ), | ||
| ); | ||
| } | ||
| } |
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