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Fix drag-and-drop termination condition bug (#5452) 

I introduced this in #5433.

TL;DR: there are two termination conditions for drag-and-drop
operations:
- ESC
- release mouse

The former _must_ happen at frame start (to properly capture the
keystroke). The latter _must_ happen at end-of-frame (to _not_ shadow
the mouse release event from user code).

This is now properly documented.
This commit is contained in:
Antoine Beyeler 2024-12-09 12:12:14 +01:00 committed by GitHub
parent 5384600fa2
commit 13352d6064
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GPG Key ID: B5690EEEBB952194
1 changed files with 19 additions and 12 deletions
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31
crates/egui/src/drag_and_drop.rs
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@ -27,31 +27,38 @@ impl DragAndDrop {
ctx.on_end_pass("drag_and_drop_end_pass", Arc::new(Self::end_pass)); ctx.on_end_pass("drag_and_drop_end_pass", Arc::new(Self::end_pass));
} }
/// Interrupt drag-and-drop if the user presses the escape key.
///
/// This needs to happen at frame start so we can properly capture the escape key.
fn begin_pass(ctx: &Context) { fn begin_pass(ctx: &Context) {
let has_any_payload = Self::has_any_payload(ctx); let has_any_payload = Self::has_any_payload(ctx);
if has_any_payload { if has_any_payload {
let abort_dnd = ctx.input_mut(|i| { let abort_dnd_due_to_escape_key =
i.pointer.any_released() ctx.input_mut(|i| i.consume_key(crate::Modifiers::NONE, crate::Key::Escape));
|| i.consume_key(crate::Modifiers::NONE, crate::Key::Escape)
});
if abort_dnd { if abort_dnd_due_to_escape_key {
Self::clear_payload(ctx); Self::clear_payload(ctx);
} }
} }
} }
/// Interrupt drag-and-drop if the user releases the mouse button.
///
/// This is a catch-all safety net in case user code doesn't capture the drag payload itself.
/// This must happen at end-of-frame such that we don't shadow the mouse release event from user
/// code.
fn end_pass(ctx: &Context) { fn end_pass(ctx: &Context) {
let mut is_dragging = false; let has_any_payload = Self::has_any_payload(ctx);
ctx.data_mut(|data| { if has_any_payload {
let state = data.get_temp_mut_or_default::<Self>(Id::NULL); let abort_dnd_due_to_mouse_release = ctx.input_mut(|i| i.pointer.any_released());
is_dragging = state.payload.is_some();
});
if is_dragging { if abort_dnd_due_to_mouse_release {
ctx.set_cursor_icon(CursorIcon::Grabbing); Self::clear_payload(ctx);
} else {
ctx.set_cursor_icon(CursorIcon::Grabbing);
}
} }
} }