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use super::*;
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/** Provides an interface between a [`Tile`] and its parent [`Pane`] during [`Tile::update`].
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All actions performed through `UpdateContext` will be executed *after* all the tiles have updated.
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## Design
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There are several factors that come into the design of [`UpdateContext`]:
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- all of its methods are considered hot-path code, which means that allocations must be kept at a minimum
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- all of the actions must be performed after all the tiles were updated
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- we need mutable access to the current tile, so that it can update its internal state
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## Example
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```
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# use stackline::{*, tile::*, context::*};
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#[derive(Clone, Debug)]
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pub struct CounterTile(usize);
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impl CounterTile {
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pub fn new() -> Self {
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Self(0)
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}
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}
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impl Tile for CounterTile {
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fn update<'b>(&'b mut self, mut ctx: UpdateContext<'b>) {
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if let Some(signal) = ctx.take_signal() {
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// Update the internal state
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self.0 += 1;
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// Send the signal along: first, get the offset (Δx, Δy) associated with its direction and the tile at (x+Δx,y+Δy)
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if let Some((pos, tile)) = ctx.get_offset(signal.direction().into_offset()) {
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// Then, check that `tile` accepts signals
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if tile.accepts_signal(signal.direction()) {
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// Finally, send the signal
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ctx.send(pos, signal).unwrap_or_else(|| unreachable!());
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}
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}
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}
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}
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}
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```
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## Safety
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Because [`Tile::update`] requires a `&mut self` reference, the current [`Tile`] cannot be accessed through [`UpdateContext::get`].
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This structure stores the [`State`] and [`Signal`] of the [`FullTile`] containing the current tile, so these can be accessed nonetheless, and it is still possible and safe to call [`UpdateContext::send`] on the current position.
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**/
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pub struct UpdateContext<'a> {
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position: (usize, usize),
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pane: &'a Pane,
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state: State,
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signal: Option<Signal>,
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commit: &'a mut UpdateCommit,
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}
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// SAFETY: self.pane.tiles[self.position] may not be accessed from any method
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impl<'a> UpdateContext<'a> {
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/// Returns `None` if the tile was already updated or is empty
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pub(crate) fn new(
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pane: &'a mut Pane,
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position: (usize, usize),
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commit: &'a mut UpdateCommit,
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) -> Option<(UpdateContext<'a>, &'a mut AnyTile)> {
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let mut tile = pane.get_mut(position)?;
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if tile.updated {
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return None;
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}
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tile.updated = true; // prevent duplicate updates
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commit.updates.push(position);
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let ptr: *mut AnyTile = &mut **(tile.get_mut().as_mut()?);
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let res = Self {
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position,
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state: tile.state(),
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signal: tile.take_signal(),
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pane,
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commit,
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};
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// SAFETY: ptr is a valid pointer
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// SAFETY: aliasing is prevented by the invariants of UpdateContext
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Some((res, unsafe { &mut *ptr }))
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}
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/// Returns the position of the currently updated tile.
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#[inline]
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pub fn position(&self) -> (usize, usize) {
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self.position
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}
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/// Returns the [signal](crate::FullTile::signal) of the currently updated tile.
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#[inline]
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pub fn signal<'b>(&'b self) -> Option<&'b Signal>
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where
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'a: 'b,
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{
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self.signal.as_ref()
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}
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/// Performs [`std::mem::take`] on the signal of the currently updated tile.
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#[inline]
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pub fn take_signal(&mut self) -> Option<Signal> {
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std::mem::take(&mut self.signal)
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}
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/// Returns the [`State`] of the current tile.
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#[inline]
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pub fn state(&self) -> State {
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self.state
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}
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/// Sets the state of the current tile to `state`.
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#[inline]
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pub fn set_state(&mut self, state: State) {
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self.commit.set_state(self.position, state);
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}
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/// Sets the state of the current tile to `state.next()`
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#[inline]
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pub fn next_state(&mut self) {
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self.commit.set_state(self.position, self.state.next());
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}
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/// Returns an immutable reference to the [FullTile] at `pos` in the current [Pane].
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/// Returns `None` if the tile is borrowed mutably, if it is the current tile or if it does not exist.
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#[inline]
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pub fn get<'b>(&'b self, pos: (usize, usize)) -> Option<&'b FullTile>
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where
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'a: 'b,
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{
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if self.position == pos {
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None
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} else {
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self.pane.get(pos)
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}
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}
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/// Returns `Some((position.x + Δx, position.y + Δy))` iff `(x + Δx, y + Δy)` is inside the pane
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#[inline]
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pub fn offset(&self, offset: (i8, i8)) -> Option<(usize, usize)> {
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self.pane.offset(self.position, offset)
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}
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/// Shortcut for calling both `ctx.offset(offset)` and `ctx.get(pos)`
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#[inline]
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pub fn get_offset<'b>(&'b self, offset: (i8, i8)) -> Option<((usize, usize), &'b FullTile)>
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where
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'a: 'b,
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{
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self.offset(offset)
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.and_then(|pos| self.get(pos).map(|tile| (pos, tile)))
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}
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/// Returns whether or not the tile at `pos` accepts a signal coming from `direction`.
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/// If the tile does not exist, then this function will return `false`.
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#[inline]
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pub fn accepts_signal(&self, pos: (usize, usize), direction: Direction) -> bool {
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match self.get(pos) {
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Some(tile) => tile.accepts_signal(direction),
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None => false,
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}
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}
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/// Sends a signal to be stored in a cell (may be the current one), the signal overrides that of the other cell
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/// Returns true if the signal was stored in a cell, false otherwise.
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/// The target cell's state will be set to `Active` if it received the signal.
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/// The signal's `position` will be set to `pos`.
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pub fn send(&mut self, pos: (usize, usize), mut signal: Signal) -> Option<()> {
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signal.set_position(pos);
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if !self.pane.in_bounds(pos) {
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return None;
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}
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self.commit.send(pos, signal);
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Some(())
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}
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}
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pub(crate) struct UpdateCommit {
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states: Vec<(usize, usize, State)>,
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signals: Vec<(usize, usize, Option<Signal>)>,
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updates: Vec<(usize, usize)>,
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}
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impl UpdateCommit {
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pub(crate) fn new() -> Self {
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Self {
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states: Vec::new(),
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signals: Vec::new(),
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updates: Vec::new(),
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}
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}
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fn send(&mut self, pos: (usize, usize), signal: Signal) {
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self.signals.push((pos.0, pos.1, Some(signal)));
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}
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fn set_state(&mut self, pos: (usize, usize), state: State) {
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self.states.push((pos.0, pos.1, state));
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}
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pub(crate) fn apply(self, pane: &mut Pane) {
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for (x, y) in self.updates {
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if let Some(tile) = pane.get_mut((x, y)) {
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tile.updated = false;
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}
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}
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for (x, y, state) in self.states {
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if let Some(tile) = pane.get_mut((x, y)) {
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tile.set_state(state);
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}
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}
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for (x, y, signal) in self.signals {
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let push_signal = if let Some(tile) = pane.get_mut((x, y)) {
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tile.set_signal(signal);
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tile.set_state(State::Active);
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// For some reason std::mem::drop(tile) isn't enough here
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true
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} else {
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false
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};
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if push_signal {
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pane.signals.push((x, y));
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}
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}
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}
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}
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