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* Closes https://github.com/emilk/egui/issues/3882 This adds several methods to make drag-and-drop more ergonomic in egui. In particular, egui can now keep track of _what_ is being dragged for you (the _payload_). Low-level: * `egui::DragAndDrop` hold the payload during a drag Mid-level: * `Response::dnd_set_drag_payload` sets it for drag-sources * `Response::dnd_hover_payload` and `Response::dnd_release_payload` reads it for drop-targets High-level: * `ui.dnd_drag_source`: make a widget draggable * `ui.dnd_drop_zone`: a container where things can be dropped The drag-and-drop demo is now a lot simpler: https://github.com/emilk/egui/blob/emilk/drag-and-drop/crates/egui_demo_lib/src/demo/drag_and_drop.rs --------- Co-authored-by: Antoine Beyeler <abeyeler@ab-ware.com>pull/3849/merge
Emil Ernerfeldt
9 months ago
committed by
GitHub
GitHub
6 changed files with 365 additions and 123 deletions
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use std::{any::Any, sync::Arc}; |
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use crate::{Context, CursorIcon, Id}; |
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/// Tracking of drag-and-drop payload.
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///
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/// This is a low-level API.
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///
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/// For a higher-level API, see:
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/// - [`crate::Ui::dnd_drag_source`]
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/// - [`crate::Ui::dnd_drop_zone`]
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/// - [`crate::Response::dnd_set_drag_payload`]
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/// - [`crate::Response::dnd_hover_payload`]
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/// - [`crate::Response::dnd_release_payload`]
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///
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/// See [this example](https://github.com/emilk/egui/blob/master/crates/egui_demo_lib/src/demo/drag_and_drop.rs).
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#[doc(alias = "drag and drop")] |
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#[derive(Clone, Default)] |
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pub struct DragAndDrop { |
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/// If set, something is currently being dragged
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payload: Option<Arc<dyn Any + Send + Sync>>, |
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} |
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impl DragAndDrop { |
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pub(crate) fn register(ctx: &Context) { |
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ctx.on_end_frame("debug_text", std::sync::Arc::new(Self::end_frame)); |
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} |
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fn end_frame(ctx: &Context) { |
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let pointer_released = ctx.input(|i| i.pointer.any_released()); |
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let mut is_dragging = false; |
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ctx.data_mut(|data| { |
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let state = data.get_temp_mut_or_default::<Self>(Id::NULL); |
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if pointer_released { |
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state.payload = None; |
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} |
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is_dragging = state.payload.is_some(); |
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}); |
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if is_dragging { |
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ctx.set_cursor_icon(CursorIcon::Grabbing); |
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} |
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} |
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/// Set a drag-and-drop payload.
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///
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/// This can be read by [`Self::payload`] until the pointer is released.
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pub fn set_payload<Payload>(ctx: &Context, payload: Payload) |
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where |
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Payload: Any + Send + Sync, |
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{ |
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ctx.data_mut(|data| { |
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let state = data.get_temp_mut_or_default::<Self>(Id::NULL); |
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state.payload = Some(Arc::new(payload)); |
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}); |
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} |
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/// Clears the payload, setting it to `None`.
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pub fn clear_payload(ctx: &Context) { |
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ctx.data_mut(|data| { |
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let state = data.get_temp_mut_or_default::<Self>(Id::NULL); |
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state.payload = None; |
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}); |
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} |
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/// Retrieve the payload, if any.
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///
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/// Returns `None` if there is no payload, or if it is not of the requested type.
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///
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/// Returns `Some` both during a drag and on the frame the pointer is released
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/// (if there is a payload).
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pub fn payload<Payload>(ctx: &Context) -> Option<Arc<Payload>> |
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where |
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Payload: Any + Send + Sync, |
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{ |
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ctx.data(|data| { |
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let state = data.get_temp::<Self>(Id::NULL)?; |
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let payload = state.payload?; |
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payload.downcast().ok() |
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}) |
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} |
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/// Retrieve and clear the payload, if any.
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///
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/// Returns `None` if there is no payload, or if it is not of the requested type.
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///
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/// Returns `Some` both during a drag and on the frame the pointer is released
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/// (if there is a payload).
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pub fn take_payload<Payload>(ctx: &Context) -> Option<Arc<Payload>> |
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where |
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Payload: Any + Send + Sync, |
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{ |
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ctx.data_mut(|data| { |
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let state = data.get_temp_mut_or_default::<Self>(Id::NULL); |
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let payload = state.payload.take()?; |
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payload.downcast().ok() |
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}) |
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} |
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/// Are we carrying a payload of the given type?
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///
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/// Returns `true` both during a drag and on the frame the pointer is released
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/// (if there is a payload).
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pub fn has_payload_of_type<Payload>(ctx: &Context) -> bool |
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where |
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Payload: Any + Send + Sync, |
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{ |
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Self::payload::<Payload>(ctx).is_some() |
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} |
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/// Are we carrying a payload?
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///
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/// Returns `true` both during a drag and on the frame the pointer is released
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/// (if there is a payload).
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pub fn has_any_payload(ctx: &Context) -> bool { |
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ctx.data(|data| { |
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let state = data.get_temp::<Self>(Id::NULL); |
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state.map_or(false, |state| state.payload.is_some()) |
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}) |
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} |
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} |
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