tweak

grid.js

@@ -0,0 +1,26 @@
+export const MAP_W = 172;
+export const MAP_H = 122;
+export const CELL_SIZE = 6;
+
+export const SIZE = MAP_W * MAP_H;
+export const INF = 1e9;
+
+export function indexOf(x, y) {
+  return y * MAP_W + x;
+}
+
+export function xyOf(i) {
+  return [i % MAP_W, Math.floor(i / MAP_W)];
+}
+
+export function inside(x, y) {
+  return x >= 0 && y >= 0 && x < MAP_W && y < MAP_H;
+}
+
+export function clamp(v, a = 0, b = 1) {
+  return Math.max(a, Math.min(b, v));
+}
+
+export function nearMapEdge(x, y, margin = 1) {
+  return x < margin || y < margin || x >= MAP_W - margin || y >= MAP_H - margin;
+}