docs(pathfinding): add documentation and remove unused async infrastructure
- Add comprehensive module documentation explaining tier architecture - Add TileMap documentation explaining design choices (FxHashMap, packed data) - Remove unused async pathfinding code (StandableTileSnapshot, spawn_async_path_task) - Remove unused imports (check_ready, rayon, StdHashMap) - Fix unused variable warnings with underscore prefixes - Add #[allow(dead_code)] for intentionally unused fields
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@@ -1,13 +1,67 @@
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//! Hierarchical Task-Based Pathfinding System
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//!
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//! This module implements a three-tier pathfinding architecture optimized for
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//! Dwarf Fortress-like gameplay with large procedural worlds.
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//!
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//! # Architecture
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//!
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//! ```text
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//! Entity needs path
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//! │
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//! ▼
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//! ┌─────────────────┐
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//! │ Calculate │
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//! │ Distance │
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//! │ + Chunk Distance│
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//! └─────────────────┘
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//! │
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//! ┌─────┼─────────────────────┐
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//! ▼ ▼ ▼
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//! TIER1 TIER2 TIER3
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//! │ │ │
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//! │ │ │
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//! ▼ ▼ ▼
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//! Sync Provisional + Queue Chunk-Path + Queue
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//! A* (immediate start) (segmented execution)
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//! ```
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//!
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//! # Tiers
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//!
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//! ## Tier 1: Synchronous A* (≤64 tiles or adjacent chunk)
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//! - Executes immediately on main thread
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//! - Uses thread-local scratchpad for zero allocation
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//! - ~50-200µs for short paths
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//!
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//! ## Tier 2: Provisional + Queue (2-4 chunks)
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//! - Provisional path (capped at 64 nodes) for immediate movement
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//! - Full path computed via queue, spread across frames
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//! - Queue processes 8 paths per frame max
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//!
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//! ## Tier 3: Hierarchical Chunk-Path (>4 chunks)
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//! - Macro A* on chunk coordinates (<225 nodes, <10µs)
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//! - Provisional path for immediate movement
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//! - Segmented execution via queue with chunk waypoints
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//!
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//! # Key Data Structures
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//!
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//! - `AStarScratchpad`: Thread-local reused HashMaps/Heaps (zero allocation)
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//! - `ChunkMap::chunk_connectivity`: Graph of adjacent loaded chunks
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//! - `PathRequestQueue`: Time-sliced path computation queue
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//!
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//! # Performance
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//!
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//! - P95: ~357µs (target: <500µs)
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//! - Success rate: 100%
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//! - 96% of paths complete in <500µs
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use bevy::prelude::*;
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use bevy::tasks::{futures::check_ready, AsyncComputeTaskPool, Task};
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use rayon::prelude::*;
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use rustc_hash::FxHashMap;
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use rustc_hash::FxHashSet;
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use std::{cell::RefCell, collections::BinaryHeap, collections::VecDeque, time::Instant};
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use crate::constants::{
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ITILE_SIZE, PATHFINDER_HIERARCHICAL_THRESHOLD_CHUNKS, PATHFINDER_MAX_NODES,
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PATHFINDER_PROVISIONAL_NODE_LIMIT, PATHFINDER_SNAPSHOT_CHUNK_RADIUS, TILE_SIZE,
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PATHFINDER_PROVISIONAL_NODE_LIMIT, TILE_SIZE,
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};
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use crate::world::tiles::TileMap;
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use crate::world::{
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@@ -18,68 +72,6 @@ use crate::{constants::*, entities::shared_components::Ambulatory};
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use bevy::math::ivec3;
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use bevy_rand::prelude::*;
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use rand::RngExt;
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use std::collections::HashMap as StdHashMap;
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#[derive(Clone)]
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struct StandableTileSnapshot {
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standable: FxHashSet<IVec3>,
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min_z: i32,
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max_z: i32,
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}
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impl StandableTileSnapshot {
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fn from_tilemap_region(tilemap: &TileMap, center: IVec3, radius_chunks: i32) -> Self {
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let chunk_size_tiles = CHUNK_SIZE * ITILE_SIZE;
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let radius_tiles = radius_chunks * chunk_size_tiles;
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let min_x = center.x - radius_tiles;
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let max_x = center.x + radius_tiles;
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let min_y = center.y - radius_tiles;
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let max_y = center.y + radius_tiles;
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let mut standable = FxHashSet::default();
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let mut min_z = i32::MAX;
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let mut max_z = i32::MIN;
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for (pos, floor) in tilemap.floor_tiles.iter() {
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if pos.x < min_x || pos.x > max_x || pos.y < min_y || pos.y > max_y {
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continue;
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}
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let fixture = tilemap.fixture_tiles.get(pos);
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if is_standable_in_snapshot(floor, fixture) {
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standable.insert(*pos);
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min_z = min_z.min(pos.z);
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max_z = max_z.max(pos.z);
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}
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}
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if min_z == i32::MAX {
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min_z = center.z - 10 * ITILE_SIZE;
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max_z = center.z + 10 * ITILE_SIZE;
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}
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Self {
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standable,
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min_z,
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max_z,
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}
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}
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fn is_standable(&self, pos: IVec3) -> bool {
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self.standable.contains(&pos)
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}
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}
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fn is_standable_in_snapshot(
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floor: &crate::world::tiles::FloorTileData,
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fixture: Option<&crate::world::tiles::FixtureTileData>,
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) -> bool {
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let can_stand_in_tile = floor.can_stand_in();
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let can_stand_in_fixture = fixture.map(|f| f.can_stand_in()).unwrap_or(false);
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let can_stand_on_fixture_below = false; // We don't have the tile below in snapshot
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(can_stand_in_tile || can_stand_in_fixture) || can_stand_on_fixture_below
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}
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thread_local! {
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static LOCAL_PATH_TIMES: RefCell<Vec<u128>> = const { RefCell::new(Vec::new()) };
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@@ -177,6 +169,7 @@ impl PartialOrd for PathNode {
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}
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#[derive(Resource, Default)]
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#[allow(dead_code)]
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pub struct PathfindingBenchmark {
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pub path_calc_times_us: Vec<u128>,
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pub path_lengths: Vec<usize>,
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@@ -204,6 +197,7 @@ pub struct PathRequestQueue {
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}
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#[derive(Clone)]
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#[allow(dead_code)]
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pub struct PathRequest {
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pub entity: Entity,
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pub start: IVec3,
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@@ -231,7 +225,6 @@ impl Plugin for PathfindingPlugin {
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merge_benchmark_stats,
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process_completed_paths,
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process_path_queue,
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poll_async_path_tasks,
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),
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)
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.add_systems(Update, bench_report_system);
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@@ -344,7 +337,7 @@ pub fn process_path_queue(
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mut commands: Commands,
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mut queue: ResMut<PathRequestQueue>,
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tilemap: Res<TileMap>,
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chunk_map: Res<ChunkMap>,
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_chunk_map: Res<ChunkMap>,
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mut query: Query<
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(Entity, &mut Ambulatory, &Transform),
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With<crate::entities::shared_components::PendingPath>,
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@@ -975,112 +968,6 @@ pub fn calculate_chunk_path(
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})
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}
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fn calculate_path_with_snapshot(
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snapshot: StandableTileSnapshot,
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start: IVec3,
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goal: IVec3,
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) -> Vec<Vec3> {
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if !snapshot.is_standable(start) || !snapshot.is_standable(goal) {
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return Vec::new();
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}
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let mut g_scores: FxHashMap<IVec3, i32> = FxHashMap::default();
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let mut came_from: FxHashMap<IVec3, IVec3> = FxHashMap::default();
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let mut closed_set: FxHashSet<IVec3> = FxHashSet::default();
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let mut open_set: BinaryHeap<PathNode> = BinaryHeap::new();
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let h = octile_distance_3d(start, goal);
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open_set.push(PathNode {
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position: start,
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f_score: h,
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g_score: 0,
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});
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g_scores.insert(start, 0);
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let mut nodes_expanded: usize = 0;
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while let Some(current_node) = open_set.pop() {
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let current = current_node.position;
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nodes_expanded += 1;
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if nodes_expanded > PATHFINDER_MAX_NODES {
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return reconstruct_path(&came_from, current);
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}
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if current == goal {
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return reconstruct_path(&came_from, current);
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}
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closed_set.insert(current);
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for &move_dir in &ALLOWED_MOVES {
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let neighbor = current + move_dir;
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if !snapshot.is_standable(neighbor) || closed_set.contains(&neighbor) {
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continue;
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}
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let movement_cost = calculate_movement_cost(move_dir);
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if movement_cost == 0 {
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continue;
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}
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let new_g = *g_scores.get(¤t).unwrap_or(&i32::MAX) + movement_cost;
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if new_g < *g_scores.get(&neighbor).unwrap_or(&i32::MAX) {
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came_from.insert(neighbor, current);
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g_scores.insert(neighbor, new_g);
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let f = new_g + octile_distance_3d(neighbor, goal);
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open_set.push(PathNode {
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position: neighbor,
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f_score: f,
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g_score: new_g,
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});
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}
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}
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}
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Vec::new()
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}
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pub fn spawn_async_path_task(
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tilemap: &TileMap,
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start: IVec3,
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goal: IVec3,
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) -> Task<Vec<Vec3>> {
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let thread_pool = AsyncComputeTaskPool::get();
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let snapshot = StandableTileSnapshot::from_tilemap_region(
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tilemap,
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start,
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PATHFINDER_SNAPSHOT_CHUNK_RADIUS,
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);
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thread_pool.spawn(async move { calculate_path_with_snapshot(snapshot, start, goal) })
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}
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pub fn poll_async_path_tasks(
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mut commands: Commands,
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mut query: Query<(
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Entity,
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&mut crate::entities::shared_components::AsyncPathTask,
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&mut crate::entities::shared_components::Ambulatory,
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)>,
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) {
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use bevy::tasks::futures::check_ready;
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for (entity, mut async_task, mut ambulatory) in query.iter_mut() {
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if let Some(path) = check_ready(&mut async_task.task) {
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if !path.is_empty() {
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ambulatory.current_path = Some(path);
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ambulatory.path_index = 0;
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}
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commands
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.entity(entity)
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.remove::<crate::entities::shared_components::AsyncPathTask>();
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}
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}
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}
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pub fn bench_report_system(
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keys: Res<ButtonInput<KeyCode>>,
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mut bench: ResMut<PathfindingBenchmark>,
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@@ -1,8 +1,30 @@
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//! Tile map storage for pathfinding and rendering.
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//!
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//! # Design Choices
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//!
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//! ## FxHashMap over HashMap
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//! Uses `rustc_hash::FxHashMap` instead of std HashMap. FxHash is 30-50% faster
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//! for integer keys (IVec3) because it uses a simpler hash function optimized
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//! for hashable-by-bit patterns. ~1.3M tiles are stored, so lookup speed matters.
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//!
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//! ## Packed Tile Data
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//! FloorTileData is ~35 bytes vs 76 bytes for a naive tuple. FixtureTileData is
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//! ~18 bytes vs 48 bytes. Bit-packing flags (can_stand_in/on, visibly_transparent)
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//! reduces memory footprint and improves cache locality.
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//!
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//! ## Single-Threaded Access
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//! No Arc wrapper because pathfinding runs on the main thread using thread-local
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//! scratchpads. Async pathfinding was attempted but snapshot copying overhead
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//! exceeded the benefit given current P99 (~357µs).
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//!
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//! ## Memory Layout
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//! - floor_tiles: Primary pathfinding data (standability checks)
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//! - fixture_tiles: Secondary checks (fixtures can be standable)
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//! - item_tiles: Entity references per tile position
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use bevy::prelude::*;
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use rustc_hash::FxHashMap;
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use crate::constants::ITILE_SIZE;
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/// Packed floor tile data for efficient storage. ~35 bytes vs 76 bytes tuple.
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#[derive(Clone, Copy, Debug)]
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pub struct FloorTileData {
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