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use crate::sim::cell_sim::sim::UpdateCtx;
#[inline]
pub fn sim_update(ctx: &mut UpdateCtx) {
// if the water can fall, do so
if ctx.candidates_swap(&[
(0, -1),
(-1 + 2 * ctx.seqno_parity as i32, -1),
(1 - 2 * ctx.seqno_parity as i32, -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.get_cell(-1, 0);
let can_move_left =
left_target.is_some_and(|c| c.material.def().density < ctx.material.density);
let right_target = ctx.get_cell(1, 0);
let can_move_right =
right_target.is_some_and(|c| c.material.def().density < ctx.material.density);
// we can't move down or to other side, so we're stuck
if !can_move_left && !can_move_right {
return;
}
// if we can't move left, just move right
if !can_move_left {
ctx.candidates_swap(&[(1, 0)]);
return;
}
// and vice versa
if !can_move_right {
ctx.candidates_swap(&[(-1, 0)]);
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
};
let offset = side * (1 + i / 2);
let hole_target = ctx.get_cell(offset, -1);
if let Some(target) = hole_target
&& target.material.def().density < ctx.material.density
{
// we identified a hole and we know that the space on this side is open
// move toward the hole
// new_target.flags = new_target.flags ^ 0b1;
ctx.candidates_swap(&[(side, 0)]);
return;
}
}
// we didn't find a hole, so just move "randomly" on the same surface
// TODO when to settle?
let target_x = if !can_move_left {
1
} else if !can_move_right {
-1
} else if ctx.seqno_parity % 2 == 1 {
1
} else {
-1
};
ctx.candidates_swap(&[(target_x, 0)]);
}
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