src/pathfinding.rs 15.4 K · 485 lines · raw · history

1 use std::{
2 cmp::Reverse,
3 collections::{BinaryHeap, HashSet, VecDeque},
4 };
5
6 use bevy::prelude::*;
7
8 use crate::world::{CHEAPEST_MOVE_COST, WorldMap};
9
10 const STRAIGHT: u32 = 10;
11 const DIAGONAL: u32 = 14;
12 const MIN_TERRAIN_COST: u32 = CHEAPEST_MOVE_COST;
13
14 const NEIGHBORS: [IVec2; 8] = [
15 IVec2::new(1, 0),
16 IVec2::new(-1, 0),
17 IVec2::new(0, 1),
18 IVec2::new(0, -1),
19 IVec2::new(1, 1),
20 IVec2::new(1, -1),
21 IVec2::new(-1, 1),
22 IVec2::new(-1, -1),
23 ];
24
25 pub fn find_path(map: &WorldMap, start: UVec2, goal: UVec2) -> Option<Vec<UVec2>> {
26 map.move_cost(goal.as_ivec2())?;
27 let goal = goal.as_ivec2();
28 astar(map, start, |p| p == goal, |p| octile(p, goal))
29 }
30
31 pub fn find_path_adjacent(map: &WorldMap, start: UVec2, target: UVec2) -> Option<Vec<UVec2>> {
32 let target = target.as_ivec2();
33 astar(
34 map,
35 start,
36 |p| is_adjacent(p, target),
37 |p| octile(p, target).saturating_sub(DIAGONAL * MIN_TERRAIN_COST),
38 )
39 }
40
41 pub fn is_adjacent(a: IVec2, b: IVec2) -> bool {
42 a != b && (a - b).abs().max_element() == 1
43 }
44
45 pub fn can_step(map: &WorldMap, from: IVec2, step: IVec2) -> bool {
46 let next = from + step;
47 map.move_cost(next).is_some()
48 && (step.x == 0
49 || step.y == 0
50 || (map.move_cost(from + IVec2::new(step.x, 0)).is_some()
51 && map.move_cost(from + IVec2::new(0, step.y)).is_some()))
52 }
53
54 pub fn nearest_tile(
55 map: &WorldMap,
56 start: UVec2,
57 max_tiles: usize,
58 mut is_target: impl FnMut(UVec2) -> bool,
59 ) -> Option<UVec2> {
60 let index = |p: UVec2| (p.y * map.size.x + p.x) as usize;
61 let mut seen = vec![false; (map.size.x * map.size.y) as usize];
62 let mut seen_count = 1;
63 if let Some(cell) = seen.get_mut(index(start)) {
64 *cell = true;
65 }
66 let mut queue = VecDeque::from([start]);
67 while let Some(pos) = queue.pop_front() {
68 if is_target(pos) {
69 return Some(pos);
70 }
71 if seen_count >= max_tiles {
72 continue;
73 }
74 for step in NEIGHBORS {
75 let next = pos.as_ivec2() + step;
76 if can_step(map, pos.as_ivec2(), step) && !seen[index(next.as_uvec2())] {
77 seen[index(next.as_uvec2())] = true;
78 seen_count += 1;
79 queue.push_back(next.as_uvec2());
80 }
81 }
82 }
83 None
84 }
85
86 #[derive(Default, Debug, Clone)]
87 pub struct Reach {
88 width: u32,
89 seen: Vec<bool>,
90 }
91
92 #[derive(Resource, Default, Debug, Clone)]
93 pub struct ColonyReach(pub Option<Reach>);
94
95 impl ColonyReach {
96 pub fn allows(&self, tile: UVec2) -> bool {
97 self.0.as_ref().is_none_or(|reach| reach.contains(tile))
98 }
99
100 pub fn allows_near(&self, tile: UVec2) -> bool {
101 self.0.as_ref().is_none_or(|reach| reach.near(tile))
102 }
103 }
104
105 impl Reach {
106 pub fn flood(map: &WorldMap, start: UVec2) -> Self {
107 let width = map.size.x;
108 let mut seen = vec![false; map.size.element_product() as usize];
109 let index = |p: UVec2| (p.y * width + p.x) as usize;
110 if map.move_cost(start.as_ivec2()).is_some() {
111 seen[index(start)] = true;
112 let mut queue = VecDeque::from([start]);
113 while let Some(pos) = queue.pop_front() {
114 for step in NEIGHBORS {
115 let next = pos.as_ivec2() + step;
116 if can_step(map, pos.as_ivec2(), step) && !seen[index(next.as_uvec2())] {
117 seen[index(next.as_uvec2())] = true;
118 queue.push_back(next.as_uvec2());
119 }
120 }
121 }
122 }
123 Self { width, seen }
124 }
125
126 pub fn contains(&self, p: UVec2) -> bool {
127 p.x < self.width
128 && self
129 .seen
130 .get((p.y * self.width + p.x) as usize)
131 .copied()
132 .unwrap_or(false)
133 }
134
135 pub fn near(&self, p: UVec2) -> bool {
136 (-1..=1).any(|dy| {
137 (-1..=1).any(|dx| {
138 let q = p.as_ivec2() + IVec2::new(dx, dy);
139 q.min_element() >= 0 && self.contains(q.as_uvec2())
140 })
141 })
142 }
143 }
144
145 pub fn search_reach(max_tiles: usize) -> u32 {
146 ((max_tiles as f32).sqrt() / 2.0).ceil() as u32
147 }
148
149 pub fn nearest_of(
150 map: &WorldMap,
151 start: UVec2,
152 max_tiles: usize,
153 targets: &HashSet<UVec2>,
154 ) -> Option<UVec2> {
155 let reach = search_reach(max_tiles) as i32;
156 let in_reach = |p: &&UVec2| (p.as_ivec2() - start.as_ivec2()).abs().max_element() <= reach;
157 if !targets.iter().any(|p| in_reach(&p)) {
158 return None;
159 }
160 nearest_tile(map, start, max_tiles, |p| targets.contains(&p))
161 }
162
163 fn astar(
164 map: &WorldMap,
165 start: UVec2,
166 is_goal: impl Fn(IVec2) -> bool,
167 heuristic: impl Fn(IVec2) -> u32,
168 ) -> Option<Vec<UVec2>> {
169 let start = start.as_ivec2();
170 if !map.in_bounds(start) {
171 return None;
172 }
173 if is_goal(start) {
174 return Some(vec![]);
175 }
176
177 let width = map.size.x as usize;
178 let index = |p: IVec2| p.y as usize * width + p.x as usize;
179 let tiles = map.size.element_product() as usize;
180 let mut cost_so_far = vec![u32::MAX; tiles];
181 let mut came_from = vec![None::<IVec2>; tiles];
182 let mut open = BinaryHeap::new();
183
184 cost_so_far[index(start)] = 0;
185 open.push(Reverse((heuristic(start), start.x, start.y)));
186
187 while let Some(Reverse((_, x, y))) = open.pop() {
188 let current = IVec2::new(x, y);
189 if is_goal(current) {
190 return Some(reconstruct(&came_from, index, start, current));
191 }
192 let current_cost = cost_so_far[index(current)];
193 for step in NEIGHBORS {
194 let next = current + step;
195 if !can_step(map, current, step) {
196 continue;
197 }
198 let Some(terrain_cost) = map.step_cost(current, next) else {
199 continue;
200 };
201 let diagonal = step.x != 0 && step.y != 0;
202 let base = if diagonal { DIAGONAL } else { STRAIGHT };
203 let new_cost = current_cost + base * terrain_cost;
204 if new_cost < cost_so_far[index(next)] {
205 cost_so_far[index(next)] = new_cost;
206 came_from[index(next)] = Some(current);
207 open.push(Reverse((new_cost + heuristic(next), next.x, next.y)));
208 }
209 }
210 }
211 None
212 }
213
214 fn octile(a: IVec2, b: IVec2) -> u32 {
215 let d = (a - b).abs();
216 let (min, max) = (d.x.min(d.y) as u32, d.x.max(d.y) as u32);
217 (DIAGONAL * min + STRAIGHT * (max - min)) * MIN_TERRAIN_COST
218 }
219
220 fn reconstruct(
221 came_from: &[Option<IVec2>],
222 index: impl Fn(IVec2) -> usize,
223 start: IVec2,
224 goal: IVec2,
225 ) -> Vec<UVec2> {
226 let mut path = vec![goal.as_uvec2()];
227 let mut current = goal;
228 while let Some(prev) = came_from[index(current)] {
229 if prev == start {
230 break;
231 }
232 path.push(prev.as_uvec2());
233 current = prev;
234 }
235 path.reverse();
236 path
237 }
238
239 #[cfg(test)]
240 mod tests {
241 use super::*;
242 use crate::world::Terrain;
243
244 // Target searches must use the same no-corner-cutting rule as A*. A stack on a tile touching
245 // the colony only diagonally between two rocks was "found" by the search, A* then explored
246 // the whole map before failing, and the job was picked again at once: ~10 ms, many times a
247 // second, which made Max speed crawl on a 50-day colony.
248 #[test]
249 fn searches_never_pick_targets_that_paths_cannot_reach() {
250 let mut map = WorldMap::filled(UVec2::splat(6), Terrain::Grass);
251 for y in 3..6 {
252 for x in 0..6 {
253 map.set(UVec2::new(x, y), Terrain::Stone);
254 }
255 }
256 map.set(UVec2::new(2, 3), Terrain::Grass);
257 map.set(UVec2::new(3, 4), Terrain::Gravel);
258 let pocket = UVec2::new(3, 4);
259 assert!(map.move_cost(IVec2::new(2, 3)).is_some());
260 assert_eq!(find_path(&map, UVec2::ZERO, pocket), None);
261 let targets = HashSet::from([pocket]);
262 assert_eq!(nearest_of(&map, UVec2::ZERO, 100, &targets), None);
263 }
264
265 // Idle colonists look for food and cooking input several times per game minute. A stack far
266 // beyond what the flood fill can cover made every one of those searches visit the full tile
267 // budget and fail, which dominated frame time at high speeds. The reach is a radius: the
268 // flood fills a square, so its half-width (not its width, as it once was) bounds it.
269 #[test]
270 fn target_searches_skip_targets_beyond_their_reach() {
271 let map = WorldMap::filled(UVec2::splat(300), Terrain::Grass);
272 let start = UVec2::splat(10);
273 let max_tiles = 400;
274 let near = start + UVec2::new(search_reach(max_tiles) / 4, 0);
275 let far = start + UVec2::new(search_reach(max_tiles) + 1, 0);
276 assert_eq!(
277 nearest_of(&map, start, max_tiles, &HashSet::from([far])),
278 None
279 );
280 assert_eq!(
281 nearest_of(&map, start, max_tiles, &HashSet::from([far, near])),
282 Some(near)
283 );
284 let edge = start + UVec2::new(search_reach(max_tiles) - 1, 0);
285 assert_eq!(
286 nearest_of(&map, start, max_tiles, &HashSet::from([edge])),
287 Some(edge)
288 );
289 }
290
291 fn map_from(rows: &[&str]) -> WorldMap {
292 let size = UVec2::new(rows[0].len() as u32, rows.len() as u32);
293 let mut map = WorldMap::filled(size, Terrain::Grass);
294 for (row, line) in rows.iter().enumerate() {
295 let y = size.y - 1 - row as u32;
296 for (x, c) in line.chars().enumerate() {
297 let terrain = match c {
298 '#' => Terrain::Stone,
299 '~' => Terrain::ShallowWater,
300 _ => Terrain::Grass,
301 };
302 map.set(UVec2::new(x as u32, y), terrain);
303 }
304 }
305 map
306 }
307
308 fn is_connected(start: UVec2, path: &[UVec2]) -> bool {
309 std::iter::once(start)
310 .chain(path.iter().copied())
311 .collect::<Vec<_>>()
312 .windows(2)
313 .all(|w| (w[0].as_ivec2() - w[1].as_ivec2()).abs().max_element() == 1)
314 }
315
316 #[test]
317 fn path_excludes_start_and_ends_at_goal() {
318 let map = map_from(&["....."]);
319 let path = find_path(&map, UVec2::new(0, 0), UVec2::new(4, 0)).unwrap();
320 assert_eq!(
321 path,
322 vec![
323 UVec2::new(1, 0),
324 UVec2::new(2, 0),
325 UVec2::new(3, 0),
326 UVec2::new(4, 0)
327 ]
328 );
329 }
330
331 #[test]
332 fn path_to_self_is_empty() {
333 let map = map_from(&["..."]);
334 assert_eq!(find_path(&map, UVec2::ZERO, UVec2::ZERO), Some(vec![]));
335 }
336
337 #[test]
338 fn path_goes_around_walls() {
339 let map = map_from(&[
340 ".....", //
341 ".###.", ".#.#.", "...#.",
342 ]);
343 let start = UVec2::new(2, 1);
344 let goal = UVec2::new(4, 0);
345 let path = find_path(&map, start, goal).unwrap();
346 assert!(is_connected(start, &path));
347 assert_eq!(path.last(), Some(&goal));
348 assert!(path.iter().all(|p| map.move_cost(p.as_ivec2()).is_some()));
349 }
350
351 #[test]
352 fn unreachable_or_impassable_goal_has_no_path() {
353 let map = map_from(&[
354 "..#..", //
355 "..#..",
356 ]);
357 assert_eq!(find_path(&map, UVec2::new(0, 0), UVec2::new(4, 0)), None);
358 assert_eq!(find_path(&map, UVec2::new(0, 0), UVec2::new(2, 0)), None);
359 }
360
361 // Colonists move in straight lines between tile centers, so a diagonal step between two
362 // blocked orthogonal neighbours would visually clip through the corners of walls.
363 #[test]
364 fn diagonal_steps_never_cut_wall_corners() {
365 let map = map_from(&[
366 "#.", //
367 ".#",
368 ]);
369 assert_eq!(find_path(&map, UVec2::new(0, 0), UVec2::new(1, 1)), None);
370 let map = map_from(&[
371 "..", //
372 "#.",
373 ]);
374 let path = find_path(&map, UVec2::new(0, 1), UVec2::new(1, 0)).unwrap();
375 assert_eq!(path, vec![UVec2::new(1, 1), UVec2::new(1, 0)]);
376 }
377
378 #[test]
379 fn prefers_detour_over_slow_terrain() {
380 let map = map_from(&[
381 ".....", //
382 "..~..",
383 ]);
384 let path = find_path(&map, UVec2::new(0, 0), UVec2::new(4, 0)).unwrap();
385 assert!(!path.contains(&UVec2::new(2, 0)));
386 }
387
388 #[test]
389 fn walks_around_a_hill_rather_than_over_it() {
390 let mut map = map_from(&[
391 ".....", //
392 ".....",
393 ]);
394 map.set_height(UVec2::new(2, 0), 10.0);
395 let path = find_path(&map, UVec2::new(0, 0), UVec2::new(4, 0)).unwrap();
396 assert!(!path.contains(&UVec2::new(2, 0)));
397 }
398
399 #[test]
400 fn detours_along_paths_when_they_are_faster() {
401 let mut map = map_from(&[
402 "..........", //
403 "..........",
404 ]);
405 for x in 0..10 {
406 map.set(UVec2::new(x, 1), Terrain::Paved);
407 }
408 let path = find_path(&map, UVec2::new(0, 0), UVec2::new(9, 0)).unwrap();
409 assert!(path.iter().filter(|p| p.y == 1).count() >= 6);
410 }
411
412 // A wall can go up on a tile a colonist is standing on (or just about to enter); routes must
413 // still start from that tile so nobody gets permanently stuck inside a wall.
414 #[test]
415 fn colonists_can_walk_out_of_a_blocked_tile() {
416 let mut map = map_from(&["....."]);
417 map.set_wall(UVec2::new(2, 0), true);
418 let path = find_path(&map, UVec2::new(2, 0), UVec2::new(4, 0)).unwrap();
419 assert_eq!(path, vec![UVec2::new(3, 0), UVec2::new(4, 0)]);
420 }
421
422 #[test]
423 fn crosses_slow_terrain_when_it_is_the_only_way() {
424 let map = map_from(&["..~.."]);
425 let path = find_path(&map, UVec2::new(0, 0), UVec2::new(4, 0)).unwrap();
426 assert!(path.contains(&UVec2::new(2, 0)));
427 }
428
429 #[test]
430 fn path_adjacent_stops_next_to_target() {
431 let map = map_from(&["......"]);
432 let path = find_path_adjacent(&map, UVec2::new(0, 0), UVec2::new(5, 0)).unwrap();
433 assert_eq!(path.last(), Some(&UVec2::new(4, 0)));
434 }
435
436 #[test]
437 fn path_adjacent_works_for_impassable_targets() {
438 let map = map_from(&["...#"]);
439 let path = find_path_adjacent(&map, UVec2::new(0, 0), UVec2::new(3, 0)).unwrap();
440 assert_eq!(path.last(), Some(&UVec2::new(2, 0)));
441 }
442
443 #[test]
444 fn path_adjacent_from_neighbor_is_empty() {
445 let map = map_from(&["..."]);
446 let path = find_path_adjacent(&map, UVec2::new(1, 0), UVec2::new(2, 0));
447 assert_eq!(path, Some(vec![]));
448 }
449
450 #[test]
451 fn path_adjacent_to_enclosed_target_is_none() {
452 let walled = map_from(&[
453 "#####", //
454 "#...#", "#####", ".....",
455 ]);
456 assert_eq!(
457 find_path_adjacent(&walled, UVec2::new(0, 0), UVec2::new(2, 2)),
458 None
459 );
460 }
461
462 #[test]
463 fn nearest_tile_finds_closest_match_by_walking_distance() {
464 let map = map_from(&[
465 ".#...", //
466 ".#.#.", "...#.",
467 ]);
468 let found = nearest_tile(&map, UVec2::new(0, 0), 100, |p| p.x == 4);
469 assert_eq!(found, Some(UVec2::new(4, 2)));
470 assert_eq!(
471 nearest_tile(&map, UVec2::new(0, 0), 100, |p| p.x == 9),
472 None
473 );
474 }
475
476 #[test]
477 fn finds_paths_across_a_generated_world() {
478 let map = crate::worldgen::generate(crate::worldgen::WORLD_SIZE, 1);
479 let region = crate::worldgen::largest_region(&map);
480 let (start, goal) = (region[0], region[region.len() - 1]);
481 let path = find_path(&map, start, goal).unwrap();
482 assert!(is_connected(start, &path));
483 assert_eq!(path.last(), Some(&goal));
484 }
485 }