feat: pathfinding

src/actors/link.js

@@ -1,14 +1,18 @@
 // Link: computer-controlled. Milestones 4-5-8 slice:
-//   seek  -> walk to the nearest pot
+//   seek  -> path to the nearest pot
 //   throw -> pick it up and hurl it (pots.js handles the arc + shatter)
-//   leave -> no pots left: walk to the exit gap and off-screen (ends the round)
-// Distractions (grass/chickens) arrive in a later milestone.
+//   leave -> no pots left: path to the exit gap and off-screen (ends the round)
+// Movement follows a BFS tile path (pathfind.js) so Link routes around terrain
+// instead of getting caught on it. Distractions arrive in a later milestone.
 
 import { TILE, LINK_SPEED } from "../config.js";
 import { visual } from "../sprites.js";
 import { throwPot } from "../pots.js";
+import { findPath } from "../pathfind.js";
 
 const INTERACT_DIST = TILE * 0.8;
+const WAYPOINT_DIST = TILE * 0.3; // how close before advancing to the next tile
+const REPATH_INTERVAL = 0.6; // seconds; recompute to self-heal if bumped
 
 export function addLink(k, world, onLeave) {
   const p = world.tc(world.level.linkSpawn);
@@ -21,19 +25,38 @@ export function addLink(k, world, onLeave) {
     "link",
   ]);
 
-  // Move toward a world position; returns distance remaining.
-  const stepToward = (target) => {
-    const d = target.sub(link.pos);
-    const dist = d.len();
-    if (dist > 1) link.move(d.unit().scale(LINK_SPEED));
-    return dist;
+  link.path = null;
+  link.pathGoal = null;
+  link.repath = 0;
+
+  // Path to `goalTile` and take one step along it. Recomputes when the goal
+  // changes, the path is spent, or the refresh timer elapses.
+  const navTo = (goalTile) => {
+    link.repath -= k.dt();
+    const from = world.toTile(link.pos);
+    const sameGoal =
+      link.pathGoal && link.pathGoal.x === goalTile.x && link.pathGoal.y === goalTile.y;
+
+    if (!sameGoal || !link.path || link.path.length === 0 || link.repath <= 0) {
+      link.path = findPath(world, from, goalTile);
+      link.pathGoal = { ...goalTile };
+      link.repath = REPATH_INTERVAL;
+    }
+
+    // Advance past any waypoint we've effectively reached.
+    while (link.path.length && link.pos.dist(world.tc(link.path[0])) <= WAYPOINT_DIST) {
+      link.path.shift();
+    }
+
+    const targetPos = link.path.length ? world.tc(link.path[0]) : world.tc(goalTile);
+    const d = targetPos.sub(link.pos);
+    if (d.len() > 1) link.move(d.unit().scale(LINK_SPEED));
   };
 
   const nearestPot = () => {
-    const pots = k.get("pot");
     let best = null;
     let bestD = Infinity;
-    for (const pot of pots) {
+    for (const pot of k.get("pot")) {
       const d = pot.pos.dist(link.pos);
       if (d < bestD) {
         bestD = d;
@@ -43,6 +66,12 @@ export function addLink(k, world, onLeave) {
     return best;
   };
 
+  const clearPath = () => {
+    link.path = null;
+    link.pathGoal = null;
+    link.repath = 0;
+  };
+
   // --- SEEK ---
   link.onStateUpdate("seek", () => {
     const pot = nearestPot();
@@ -50,14 +79,17 @@ export function addLink(k, world, onLeave) {
       link.enterState("leave");
       return;
     }
-    if (stepToward(pot.pos) <= INTERACT_DIST) {
+    if (pot.pos.dist(link.pos) <= INTERACT_DIST) {
       link.target = pot;
       link.enterState("throw");
+      return;
     }
+    navTo(world.toTile(pot.pos));
   });
 
   // --- THROW ---
   link.onStateEnter("throw", () => {
+    clearPath();
     const pot = link.target;
     if (!pot || pot.destroyed) {
       link.enterState("seek");
@@ -65,28 +97,25 @@ export function addLink(k, world, onLeave) {
     }
     const at = pot.pos.clone();
     pot.destroy(); // picked up
-    link.throwing = true;
-    throwPot(k, world, at, () => {
-      link.throwing = false;
-      link.enterState("seek");
-    });
+    throwPot(k, world, at, () => link.enterState("seek"));
   });
   // Stand still while the throw animation plays.
 
   // --- LEAVE ---
   link.onStateEnter("leave", () => {
+    clearPath();
     link.leaving = true;
   });
   link.onStateUpdate("leave", () => {
     const exitPos = world.tc(world.level.exit);
-    stepToward(exitPos);
-    // Once he reaches / passes the exit gap, he's gone.
     if (link.pos.dist(exitPos) < TILE * 0.5) {
       if (!link.gone) {
         link.gone = true;
         onLeave && onLeave();
       }
+      return;
     }
+    navTo(world.level.exit);
   });
 
   link.onUpdate(() => {

src/pathfind.js

@@ -0,0 +1,50 @@
+// Breadth-first shortest path over walkable tiles (4-directional).
+//
+// Link steers directly toward his target, which means solid terrain between him
+// and a pot would trap him. Routing along a tile path of only walkable tiles
+// keeps him off obstacles/walls, and because steps are orthogonal he never cuts
+// a corner into a solid tile.
+
+const key = (x, y) => `${x},${y}`;
+const NEIGHBORS = [
+  [1, 0],
+  [-1, 0],
+  [0, 1],
+  [0, -1],
+];
+
+// Returns the list of tiles AFTER `from` up to and including `goal`, or [] if
+// the goal is unreachable / equals the start (callers fall back to direct steer).
+export function findPath(world, from, goal) {
+  if (from.x === goal.x && from.y === goal.y) return [];
+  if (!world.walkable(goal.x, goal.y)) return [];
+
+  const prev = new Map();
+  const seen = new Set([key(from.x, from.y)]);
+  const queue = [from];
+  let head = 0;
+
+  while (head < queue.length) {
+    const cur = queue[head++];
+    if (cur.x === goal.x && cur.y === goal.y) {
+      const path = [];
+      let c = cur;
+      while (!(c.x === from.x && c.y === from.y)) {
+        path.push(c);
+        c = prev.get(key(c.x, c.y));
+      }
+      return path.reverse();
+    }
+    for (const [dx, dy] of NEIGHBORS) {
+      const nx = cur.x + dx;
+      const ny = cur.y + dy;
+      if (!world.walkable(nx, ny)) continue;
+      const kk = key(nx, ny);
+      if (seen.has(kk)) continue;
+      seen.add(kk);
+      prev.set(kk, { ...cur });
+      queue.push({ x: nx, y: ny });
+    }
+  }
+  return [];
+}

src/scenes/game.js

@@ -8,7 +8,9 @@ import { addLink } from "../actors/link.js";
 
 export function registerGameScene(k) {
   k.scene("game", (opts = {}) => {
-    const seed = opts.seed ?? Math.floor(Math.random() * 1e9);
+    const urlSeed = Number(new URLSearchParams(location.search).get("seed"));
+    const seed =
+      opts.seed ?? (Number.isFinite(urlSeed) && urlSeed > 0 ? urlSeed : Math.floor(Math.random() * 1e9));
     const level = generate(k, seed);
     let roundOver = false;