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|
use glam::{IVec2, Vec2};
/**
0b(tl)(tr)(br)(bl), 0..=15
0 0000 - -
1 0001 BL S → W
2 0010 BR E → S
3 0011 BL BR E → W
4 0100 TR N → E
5 0101 TR BL saddle: N → W, S → E
6 0110 TR BR N → S
7 0111 TR BR BL N → W
8 1000 TL W → N
9 1001 TL BL S → N
10 1010 TL BR saddle: E → N, W → S
11 1011 TL BR BL E → N
12 1100 TL TR W → E
13 1101 TL TR BL S → E
14 1110 TL TR BR W → S
15 1111 - -
*/
#[inline]
fn derive_type(tl: bool, tr: bool, br: bool, bl: bool) -> usize {
bl as usize | (br as usize) << 1 | (tr as usize) << 2 | (tl as usize) << 3
}
pub trait Marchable {
fn occupied(&self, pos: IVec2) -> bool;
fn marchable_size(&self) -> IVec2;
}
pub fn compute_types(marchable: &impl Marchable) -> Vec<u8> {
// TODO could pre-allocate size
let mut types = Vec::new();
for y in -1..marchable.marchable_size().y {
// TODO precompute per column
for x in -1..marchable.marchable_size().x {
let tl = marchable.occupied(IVec2::new(x, y));
let tr = marchable.occupied(IVec2::new(x + 1, y));
let br = marchable.occupied(IVec2::new(x + 1, y + 1));
let bl = marchable.occupied(IVec2::new(x, y + 1));
types.push(derive_type(tl, tr, br, bl) as u8);
}
}
types
}
#[derive(PartialEq, Eq, Clone, Copy)]
enum Side {
None,
N,
E,
S,
W,
}
const EDGE_COUNT_BY_TYPE: [usize; 16] = [0, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 0];
const EDGE_START_BY_TYPE_BY_IDX: [[Side; 2]; 16] = [
[Side::None, Side::None],
[Side::S, Side::None],
[Side::E, Side::None],
[Side::E, Side::None],
[Side::N, Side::None],
[Side::N, Side::S],
[Side::N, Side::None],
[Side::N, Side::None],
[Side::W, Side::None],
[Side::S, Side::None],
[Side::E, Side::W],
[Side::E, Side::None],
[Side::W, Side::None],
[Side::S, Side::None],
[Side::W, Side::None],
[Side::None, Side::None],
];
const EDGE_END_BY_TYPE: [[Side; 2]; 16] = [
[Side::None, Side::None],
[Side::W, Side::None],
[Side::S, Side::None],
[Side::W, Side::None],
[Side::E, Side::None],
[Side::W, Side::E],
[Side::S, Side::None],
[Side::W, Side::None],
[Side::N, Side::None],
[Side::N, Side::None],
[Side::N, Side::S],
[Side::N, Side::None],
[Side::E, Side::None],
[Side::E, Side::None],
[Side::S, Side::None],
[Side::None, Side::None],
];
fn side_centre(x: i32, y: i32, s: Side) -> Vec2 {
let (x, y) = (x as f32, y as f32);
match s {
Side::N => Vec2::new(x + 0.5, y),
Side::E => Vec2::new(x + 1.0, y + 0.5),
Side::S => Vec2::new(x + 0.5, y + 1.0),
Side::W => Vec2::new(x, y + 0.5),
Side::None => panic!("Tried to access None side"),
}
}
fn toward_side(x: i32, y: i32, exit: Side) -> (i32, i32, Side) {
match exit {
Side::N => (x, y - 1, Side::S),
Side::E => (x + 1, y, Side::W),
Side::S => (x, y + 1, Side::N),
Side::W => (x - 1, y, Side::E),
Side::None => panic!("Tried to access None side"),
}
}
// outer is cw, inner ccw
pub fn marching_squares_vertex_trace(marchable: &impl Marchable) -> Vec<Vec<Vec2>> {
let [w, h] = marchable.marchable_size().to_array();
let mut visited = vec![0u8; ((w + 1) * (h + 1)) as usize];
let idx = |cx: i32, cy: i32| (((cy + 1) * (w + 1)) + (cx + 1)) as usize;
let types = compute_types(marchable);
let mut polys = Vec::new();
for y in -1..h {
for x in -1..w {
let mut t = types[(x + 1 + (y + 1) * (w + 1)) as usize] as usize;
// if there are multiple edges for this type (saddle), try to build a poly for each
for e in 0..EDGE_COUNT_BY_TYPE[t] {
// if we have already visited this cell FOR this edge, skip
if visited[idx(x, y)] & (1 << e) != 0 {
continue;
}
let mut poly = Vec::new();
let (mut xi, mut yi, mut ei) = (x, y, e);
// keep collecting until we don't connect to an edge
loop {
// if we have already visited this cell FOR this edge, skip
if visited[idx(xi, yi)] & (1 << ei) != 0 {
break;
}
// set this on the inner loop since every cell we take on the loop is claimed
visited[idx(xi, yi)] |= 1 << ei;
// this edge starts and ends against some side of our cell
let (start, end) = (EDGE_START_BY_TYPE_BY_IDX[t][ei], EDGE_END_BY_TYPE[t][ei]);
poly.push(side_centre(xi, yi, start));
// move ourselves into the cell that our edge ends in, unless it's out of the grid
let (nx, ny, entry) = toward_side(xi, yi, end);
// TODO is equality cheaper?
if nx < -1 || nx >= w || ny < -1 || ny >= h {
// exited the board
panic!(
"Expecting closed loop but it's not (off the board)! Came from ({xi}, {yi}, {ei}) to ({nx}, {ny})"
)
}
let nt = types[(nx + 1 + (ny + 1) * (w + 1)) as usize] as usize;
if EDGE_START_BY_TYPE_BY_IDX[nt][0] == entry {
// there's an edge starting where we entered
xi = nx;
yi = ny;
ei = 0;
t = nt;
} else if EDGE_START_BY_TYPE_BY_IDX[nt][1] == entry {
// entering the other side of the saddle
xi = nx;
yi = ny;
ei = 1;
t = nt;
} else {
panic!(
"Expecting closed loop but it's not! Came from ({xi}, {yi}, {ei}) to ({nx}, {ny})"
)
}
}
polys.push(poly);
}
}
}
polys
}
|
