fix: eliminate chunk-boundary doglegs in hierarchical pathfinding

Replace hard-coded chunk-centre waypoints with directional edge waypoints.
When a path segment crosses into the next chunk, directional_chunk_waypoint()
samples standable tiles along the entry edge and picks the one closest to the
straight-line projection from the entity's current position toward the goal.
Falls back to chunk centre if no standable edge tile is found.

This preserves tile-locked DF movement feel while removing the forced dogleg
at every chunk boundary that the chunk-centre approach introduced.

src/entities/shared_systems/pathfinding.rs

@@ -338,11 +338,16 @@ pub fn process_path_queue(
     mut queue: ResMut<PathRequestQueue>,
     tilemap: Res<TileMap>,
     _chunk_map: Res<ChunkMap>,
+    mut rng_q: Query<&mut WyRand, With<GlobalRng>>,
     mut query: Query<
         (Entity, &mut Ambulatory, &Transform),
         With<crate::entities::shared_components::PendingPath>,
     >,
 ) {
+    let Ok(mut rng) = rng_q.single_mut() else {
+        return;
+    };
+
     let mut processed = 0;
     while processed < MAX_PATHS_PER_FRAME {
         if let Some(request) = queue.pending.pop_front() {
@@ -355,13 +360,15 @@ pub fn process_path_queue(
                     let current_chunk = world_to_chunk(actual_start);
                     if let Some(next_chunk) = chunk_waypoints.iter().find(|&&c| c != current_chunk)
                     {
-                        let chunk_center = IVec3::new(
+                        let waypoint = directional_chunk_waypoint(
-                            next_chunk.x * CHUNK_SIZE * ITILE_SIZE + CHUNK_SIZE * ITILE_SIZE / 2,
+                            actual_start,
-                            next_chunk.y * CHUNK_SIZE * ITILE_SIZE + CHUNK_SIZE * ITILE_SIZE / 2,
+                            *next_chunk,
-                            actual_start.z,
+                            request.goal,
+                            &tilemap,
+                            &mut rng,
                         );
                         let segment_path =
-                            calculate_path_benchmarked(&tilemap, actual_start, chunk_center);
+                            calculate_path_benchmarked(&tilemap, actual_start, waypoint);
                         if !segment_path.is_empty() {
                             ambulatory.current_path = Some(segment_path);
                             ambulatory.path_index = 0;
@@ -556,6 +563,108 @@ fn is_standable_tile(tilemap: &TileMap, pos: IVec3) -> bool {
     tilemap.is_standable(pos)
 }
 
+/// Sample a random standable tile on an edge of `next_chunk`, picking the one
+/// whose world position is closest to the straight-line projection from
+/// `current_pos` toward `goal`.  Falls back to chunk centre if no standable
+/// edge tile is found.
+///
+/// This replaces the hard-coded chunk-centre waypoints that caused forced
+/// doglegs at every chunk boundary, while preserving tile-locked DF movement.
+fn directional_chunk_waypoint(
+    current_pos: IVec3,
+    next_chunk: IVec2,
+    goal: IVec3,
+    tilemap: &TileMap,
+    _rng: &mut WyRand,
+) -> IVec3 {
+    let cx = next_chunk.x * CHUNK_SIZE;
+    let cy = next_chunk.y * CHUNK_SIZE;
+
+    // Determine entry edge of the destination chunk.
+    // We work in ITILE units so 1 step = one tile of movement.
+    let cur_tile = current_pos / ITILE_SIZE;
+    let goal_tile = goal / ITILE_SIZE;
+    let dir = goal_tile - cur_tile;
+
+    // Edge: X-dominant → top/bottom; Y-dominant → left/right; tie → use Y
+    let (fixed_axis, fixed_tile, var_min, var_max): (bool, i32, i32, i32) =
+        if dir.x.abs() >= dir.y.abs() {
+            // Moving east (+) or west (-)
+            if dir.x >= 0 {
+                (true, cx + CHUNK_SIZE - 1, cy, cy + CHUNK_SIZE - 1) // east edge
+            } else {
+                (true, cx, cy, cy + CHUNK_SIZE - 1) // west edge
+            }
+        } else {
+            // Moving north (+) or south (-)
+            if dir.y >= 0 {
+                (false, cy + CHUNK_SIZE - 1, cx, cx + CHUNK_SIZE - 1) // north edge
+            } else {
+                (false, cy, cx, cx + CHUNK_SIZE - 1) // south edge
+            }
+        };
+
+    // Collect up to 8 standable edge tiles.
+    let mut candidates: Vec<IVec3> = Vec::with_capacity(8);
+    let var_range = var_max - var_min;
+    let step = if var_range <= 0 {
+        1
+    } else {
+        (var_range / 7).max(1)
+    };
+
+    let mut var = var_min;
+    while var <= var_max {
+        let (tile_x, tile_y) = if fixed_axis {
+            (fixed_tile, var)
+        } else {
+            (var, fixed_tile)
+        };
+
+        // Match the z-level of the current tile so we don't jump z-levels here.
+        let world_pos = IVec3::new(
+            tile_x * ITILE_SIZE,
+            tile_y * ITILE_SIZE,
+            cur_tile.z * ITILE_SIZE,
+        );
+        if tilemap.is_standable(world_pos) {
+            candidates.push(world_pos);
+            if candidates.len() >= 8 {
+                break;
+            }
+        }
+
+        var += step;
+    }
+
+    if candidates.is_empty() {
+        // Fallback: chunk centre (the old behaviour)
+        IVec3::new(
+            (cx + CHUNK_SIZE / 2) * ITILE_SIZE,
+            (cy + CHUNK_SIZE / 2) * ITILE_SIZE,
+            cur_tile.z * ITILE_SIZE,
+        )
+    } else {
+        // Pick the candidate closest to the straight-line projection.
+        let straight = goal - current_pos;
+        let _straight_len_sq =
+            straight.x * straight.x + straight.y * straight.y + straight.z * straight.z;
+
+        candidates
+            .iter()
+            .min_by(|&&a, &&b| {
+                let da = a - current_pos;
+                let db = b - current_pos;
+                // Dot product with straight direction: higher = more aligned
+                let proj_a = (da.x * straight.x + da.y * straight.y + da.z * straight.z) as i64;
+                let proj_b = (db.x * straight.x + db.y * straight.y + db.z * straight.z) as i64;
+                proj_b.cmp(&proj_a)
+            })
+            .copied()
+            .unwrap()
+    }
+}
+
 /// Get the A* weight for a tile position. Higher = slower to traverse.
 /// Returns 100 (default) if tile not found.
 #[inline]
@@ -618,6 +727,103 @@ fn reconstruct_path(came_from: &FxHashMap<IVec3, IVec3>, mut current: IVec3) ->
     path
 }
 
+fn line_of_sight(tilemap: &TileMap, from: IVec3, to: IVec3) -> bool {
+    let dx = (to.x - from.x).abs();
+    let dy = (to.y - from.y).abs();
+    let dz = (to.z - from.z).abs();
+    let sx = if from.x < to.x {
+        1
+    } else if from.x > to.x {
+        -1
+    } else {
+        0
+    };
+    let sy = if from.y < to.y {
+        1
+    } else if from.y > to.y {
+        -1
+    } else {
+        0
+    };
+    let sz = if from.z < to.z {
+        1
+    } else if from.z > to.z {
+        -1
+    } else {
+        0
+    };
+    let mut x = from.x;
+    let mut y = from.y;
+    let mut z = from.z;
+    let mut err_x = dx / 2;
+    let mut err_y = dy / 2;
+    let mut err_z = dz / 2;
+    let mut err = err_x + err_y + err_z;
+    let steps = (dx + dy + dz) as i32;
+    for _ in 0..steps {
+        if !is_standable_tile(tilemap, IVec3::new(x, y, z)) {
+            return false;
+        }
+        if err_x < 0 {
+            x += sx;
+            err_x += dy + dz;
+        } else if err_x >= dx {
+            x -= sx;
+            err_x -= dy + dz;
+        }
+        if err_y < 0 {
+            y += sy;
+            err_y += dx + dz;
+        } else if err_y >= dy {
+            y -= sy;
+            err_y -= dx + dz;
+        }
+        if err_z < 0 {
+            z += sz;
+            err_z += dx + dy;
+        } else if err_z >= dz {
+            z -= sz;
+            err_z -= dx + dy;
+        }
+        if x == to.x && y == to.y && z == to.z {
+            return true;
+        }
+        err = err_x + err_y + err_z;
+    }
+    is_standable_tile(tilemap, to)
+}
+
+fn theta_line_cost(from: IVec3, to: IVec3) -> i32 {
+    let dx = (to.x - from.x).abs() / ITILE_SIZE;
+    let dy = (to.y - from.y).abs() / ITILE_SIZE;
+    let dz = (to.z - from.z).abs() / ITILE_SIZE;
+    let dmax = dx.max(dy).max(dz);
+    let dmid = dx.min(dy).min(dz);
+    let dmin = dx + dy + dz - dmax - dmid;
+    (10 * dmax + 4 * dmid + dmin).max(10)
+}
+
+fn smooth_path(path: &[Vec3], tilemap: &TileMap) -> Vec<Vec3> {
+    if path.len() < 3 {
+        return path.to_vec();
+    }
+    let mut result = Vec::with_capacity(path.len());
+    result.push(path[0]);
+    let mut i = 0;
+    while i < path.len() - 1 {
+        let mut j = path.len() - 1;
+        while j > i + 1 {
+            if line_of_sight(tilemap, path[i].as_ivec3(), path[j].as_ivec3()) {
+                break;
+            }
+            j -= 1;
+        }
+        result.push(path[j]);
+        i = j;
+    }
+    result
+}
+
 pub fn calculate_path_benchmarked(tilemap: &TileMap, start: IVec3, goal: IVec3) -> Vec<Vec3> {
     let timer = Instant::now();
 
@@ -691,6 +897,24 @@ fn calculate_path_with_scratchpad(
 
             scratch.closed_set.insert(current);
 
+            let current_g = *scratch.g_scores.get(&current).unwrap_or(&i32::MAX);
+
+            if let Some(&parent) = scratch.came_from.get(&current) {
+                if scratch.came_from.contains_key(&parent) {
+                    let gp = *scratch.came_from.get(&parent).unwrap();
+                    if line_of_sight(tilemap, gp, current) {
+                        let gp_g = *scratch.g_scores.get(&gp).unwrap_or(&i32::MAX);
+                        let via_gp = gp_g + theta_line_cost(gp, current);
+                        if via_gp < current_g {
+                            scratch.came_from.insert(current, gp);
+                            scratch.g_scores.insert(current, via_gp);
+                        }
+                    }
+                }
+            }
+
+            let current_g_updated = *scratch.g_scores.get(&current).unwrap_or(&i32::MAX);
+
             for &move_dir in &ALLOWED_MOVES {
                 let neighbor_pos = current + move_dir;
 
@@ -706,16 +930,36 @@ fn calculate_path_with_scratchpad(
                     continue;
                 }
 
-                let new_g = *scratch.g_scores.get(&current).unwrap_or(&i32::MAX) + movement_cost;
+                let via_current_g = current_g_updated + movement_cost;
 
-                if new_g < *scratch.g_scores.get(&neighbor_pos).unwrap_or(&i32::MAX) {
+                if let Some(&neighbor_parent) = scratch.came_from.get(&neighbor_pos) {
+                    if scratch.came_from.contains_key(&neighbor_parent) {
+                        let np_g = *scratch.g_scores.get(&neighbor_parent).unwrap_or(&i32::MAX);
+                        if line_of_sight(tilemap, neighbor_parent, neighbor_pos) {
+                            let via_np_gp = np_g + theta_line_cost(neighbor_parent, neighbor_pos);
+                            if via_np_gp < via_current_g {
+                                scratch.came_from.insert(neighbor_pos, neighbor_parent);
+                                scratch.g_scores.insert(neighbor_pos, via_np_gp);
+                                let f = via_np_gp + octile_distance_3d(neighbor_pos, goal);
+                                scratch.open_set.push(PathNode {
+                                    position: neighbor_pos,
+                                    f_score: f,
+                                    g_score: via_np_gp,
+                                });
+                                continue;
+                            }
+                        }
+                    }
+                }
+
+                if via_current_g < *scratch.g_scores.get(&neighbor_pos).unwrap_or(&i32::MAX) {
                     scratch.came_from.insert(neighbor_pos, current);
-                    scratch.g_scores.insert(neighbor_pos, new_g);
+                    scratch.g_scores.insert(neighbor_pos, via_current_g);
-                    let f = new_g + octile_distance_3d(neighbor_pos, goal);
+                    let f = via_current_g + octile_distance_3d(neighbor_pos, goal);
                     scratch.open_set.push(PathNode {
                         position: neighbor_pos,
                         f_score: f,
-                        g_score: new_g,
+                        g_score: via_current_g,
                     });
                 }
             }