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use crate::sim::sim::UpdateCtx;
#[inline]
pub fn sim_update(ctx: &mut UpdateCtx) {
// if the water can fall, do so
if ctx.candidates_swap(&[
(ctx.self_x, ctx.self_y + 1),
(ctx.self_x - 1 + 2 * ctx.seqno_parity as i32, ctx.self_y + 1),
(ctx.self_x + 1 - 2 * ctx.seqno_parity as i32, ctx.self_y + 1),
]) {
return;
}
// if the water can't fall, check if we can move left or right
// these are inverted on parity so that we don't preference a direction
let left_target = ctx.board.cell_at_position(ctx.self_x - 1, ctx.self_y);
let can_move_left = left_target
.is_some_and(|c| c.material.def().density < ctx.self_cell.material.def().density);
let right_target = ctx.board.cell_at_position(ctx.self_x + 1, ctx.self_y);
let can_move_right = right_target
.is_some_and(|c| c.material.def().density < ctx.self_cell.material.def().density);
// we can't move down or to other side, so we're stuck
if !can_move_left && !can_move_right {
return;
}
// find the closest hole within 20 pixels (TODO optimize)
// a hole is any space below us with a lesser density
// prevents equidistance stuck state
let starting_side = if ctx.seqno_parity == 0 { 1 } else { -1 };
for i in 0..20 {
let side = if i % 2 == 0 {
starting_side
} else {
-starting_side
};
if (side == 1 && !can_move_right) || (side == -1 && !can_move_left) {
continue;
}
let offset = side * (1 + i / 2);
let hole_target = ctx
.board
.cell_at_position(ctx.self_x + offset, ctx.self_y + 1);
if let Some(target) = hole_target
&& target.material.def().density < ctx.self_cell.material.def().density
{
// we identified a hole and we know that the space on this side is open
// move toward the hole
let move_target = if side == 1 { right_target } else { left_target }.clone();
// new_target.flags = new_target.flags ^ 0b1;
// safe to unwrap
ctx.board
.set_cell_at_position(ctx.self_x, ctx.self_y, move_target.unwrap());
ctx.board
.set_cell_at_position(ctx.self_x + side, ctx.self_y, ctx.self_cell);
return;
}
}
// we didn't find a hole, so just move "randomly" on the same surface
// TODO when to settle?
let (target, target_x) = if !can_move_left {
(right_target, 1)
} else if !can_move_right {
(left_target, -1)
} else if ctx.seqno_parity % 2 == 1 {
(right_target, 1)
} else {
(left_target, -1)
};
ctx.board
.set_cell_at_position(ctx.self_x, ctx.self_y, target.unwrap());
ctx.board
.set_cell_at_position(ctx.self_x + target_x, ctx.self_y, ctx.self_cell);
}
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