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Picking out order (#16231)

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Tweaks picking docs slightly for formatting and to add additional
context about the ordering of `Over` and `Out` events. Also shifts `Out`
to trigger before `Over` in the global event ordering.

Because of how focus is tracked, we must send all `Over` and `Out`
events at the same time, in a block. Originally I had `Over` precede
`Out` in the global event order, because this seemed natural. However,
the effect of this, when a pointer moves between entities, is to have
the new entity receive `Over` before the old entity received `Out`,
which several users found confusing.

The new ordering (out before over globally, over before out locally per
entity) should make it much easier to write hover state cleanup code.
This commit is contained in:
Miles Silberling-Cook 2024-11-15 10:39:02 -05:00 committed by François Mockers
parent d2debf2cc9
commit 85ade64dc4
1 changed files with 91 additions and 68 deletions
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159
crates/bevy_picking/src/events.rs
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@ -321,28 +321,51 @@ pub struct PickingEventWriters<'w> {
/// Dispatches interaction events to the target entities.
///
/// Within a single frame, events are dispatched in the following order:
/// + The sequence [`DragEnter`], [`Over`].
/// + [`Out`] → [`DragLeave`].
/// + [`DragEnter`] → [`Over`].
/// + Any number of any of the following:
/// + For each movement: The sequence [`DragStart`], [`Drag`], [`DragOver`], [`Move`].
/// + For each button press: Either [`Down`], or the sequence [`Click`], [`Up`], [`DragDrop`], [`DragEnd`], [`DragLeave`].
/// + For each pointer cancellation: Simply [`Cancel`].
/// + Finally the sequence [`Out`], [`DragLeave`].
/// + For each movement: [`DragStart`] → [`Drag`] → [`DragOver`] → [`Move`].
/// + For each button press: [`Down`] or [`Click`] → [`Up`] → [`DragDrop`] → [`DragEnd`] → [`DragLeave`].
/// + For each pointer cancellation: [`Cancel`].
///
/// Only the last event in a given sequence is garenteed to be present.
/// Additionally, across multiple frames, the following are also strictly
/// ordered by the interaction state machine:
/// + When a pointer moves over the target:
/// [`Over`], [`Move`], [`Out`].
/// + When a pointer presses buttons on the target:
/// [`Down`], [`Click`], [`Up`].
/// + When a pointer drags the target:
/// [`DragStart`], [`Drag`], [`DragEnd`].
/// + When a pointer drags something over the target:
/// [`DragEnter`], [`DragOver`], [`DragDrop`], [`DragLeave`].
/// + When a pointer is canceled:
/// No other events will follow the [`Cancel`] event for that pointer.
///
/// Additionally, across multiple frames, the following are also strictly ordered by the interaction state machine:
/// + When a pointer moves over the target: [`Over`], [`Move`], [`Out`].
/// + When a pointer presses buttons on the target: [`Down`], [`Up`], [`Click`].
/// + When a pointer drags the target: [`DragStart`], [`Drag`], [`DragEnd`].
/// + When a pointer drags something over the target: [`DragEnter`], [`DragOver`], [`DragDrop`], [`DragLeave`].
/// + When a pointer is canceled: No other events will follow the [`Cancel`] event for that pointer.
/// Two events -- [`Over`] and [`Out`] -- are driven only by the [`HoverMap`].
/// The rest rely on additional data from the [`PointerInput`] event stream. To
/// receive these events for a custom pointer, you must add [`PointerInput`]
/// events.
///
/// Two events -- [`Over`] and [`Out`] -- are driven only by the [`HoverMap`]. The rest rely on additional data from the
/// [`PointerInput`] event stream. To receive these events for a custom pointer, you must add [`PointerInput`] events.
/// When the pointer goes from hovering entity A to entity B, entity A will
/// receive [`Out`] and then entity B will receive [`Over`]. No entity will ever
/// receive both an [`Over`] and and a [`Out`] event during the same frame.
///
/// Note: Though it is common for the [`PointerInput`] stream may contain multiple pointer movements and presses each frame,
/// the hover state is determined only by the pointer's *final position*. Since the hover state ultimately determines which
/// entities receive events, this may mean that an entity can receive events which occurred before it was actually hovered.
/// When we account for event bubbling, this is no longer true. When focus shifts
/// between children, parent entities may receive redundant [`Out`] → [`Over`] pairs.
/// In the context of UI, this is especially problematic. Additional hierarchy-aware
/// events will be added in a future release.
///
/// Both [`Click`] and [`Up`] target the entity hovered in the *previous frame*,
/// rather than the current frame. This is because touch pointers hover nothing
/// on the frame they are released. The end effect is that these two events can
/// be received sequentally after an [`Out`] event (but always on the same frame
/// as the [`Out`] event).
///
/// Note: Though it is common for the [`PointerInput`] stream may contain
/// multiple pointer movements and presses each frame, the hover state is
/// determined only by the pointer's *final position*. Since the hover state
/// ultimately determines which entities receive events, this may mean that an
/// entity can receive events from before or after it was actually hovered.
#[allow(clippy::too_many_arguments)]
pub fn pointer_events(
// Input
@ -366,6 +389,57 @@ pub fn pointer_events(
.and_then(|pointer| pointer.location.clone())
};
// If the entity was hovered by a specific pointer last frame...
for (pointer_id, hovered_entity, hit) in previous_hover_map
.iter()
.flat_map(|(id, hashmap)| hashmap.iter().map(|data| (*id, *data.0, data.1.clone())))
{
// ...but is now not being hovered by that same pointer...
if !hover_map
.get(&pointer_id)
.iter()
.any(|e| e.contains_key(&hovered_entity))
{
let Some(location) = pointer_location(pointer_id) else {
debug!(
"Unable to get location for pointer {:?} during pointer out",
pointer_id
);
continue;
};
// Always send Out events
let out_event = Pointer::new(
hovered_entity,
pointer_id,
location.clone(),
Out { hit: hit.clone() },
);
commands.trigger_targets(out_event.clone(), hovered_entity);
event_writers.out_events.send(out_event);
// Possibly send DragLeave events
for button in PointerButton::iter() {
let state = pointer_state.get_mut(pointer_id, button);
state.dragging_over.remove(&hovered_entity);
for drag_target in state.dragging.keys() {
let drag_leave_event = Pointer::new(
hovered_entity,
pointer_id,
location.clone(),
DragLeave {
button,
dragged: *drag_target,
hit: hit.clone(),
},
);
commands.trigger_targets(drag_leave_event.clone(), hovered_entity);
event_writers.drag_leave_events.send(drag_leave_event);
}
}
}
}
// If the entity is hovered...
for (pointer_id, hovered_entity, hit) in hover_map
.iter()
@ -659,55 +733,4 @@ pub fn pointer_events(
}
}
}
// If the entity was hovered by a specific pointer last frame...
for (pointer_id, hovered_entity, hit) in previous_hover_map
.iter()
.flat_map(|(id, hashmap)| hashmap.iter().map(|data| (*id, *data.0, data.1.clone())))
{
// ...but is now not being hovered by that same pointer...
if !hover_map
.get(&pointer_id)
.iter()
.any(|e| e.contains_key(&hovered_entity))
{
let Some(location) = pointer_location(pointer_id) else {
debug!(
"Unable to get location for pointer {:?} during pointer out",
pointer_id
);
continue;
};
// Always send Out events
let out_event = Pointer::new(
hovered_entity,
pointer_id,
location.clone(),
Out { hit: hit.clone() },
);
commands.trigger_targets(out_event.clone(), hovered_entity);
event_writers.out_events.send(out_event);
// Possibly send DragLeave events
for button in PointerButton::iter() {
let state = pointer_state.get_mut(pointer_id, button);
state.dragging_over.remove(&hovered_entity);
for drag_target in state.dragging.keys() {
let drag_leave_event = Pointer::new(
hovered_entity,
pointer_id,
location.clone(),
DragLeave {
button,
dragged: *drag_target,
hit: hit.clone(),
},
);
commands.trigger_targets(drag_leave_event.clone(), hovered_entity);
event_writers.drag_leave_events.send(drag_leave_event);
}
}
}
}
}