diff --git a/public/tile-map.png b/public/tile-map.png
index 255c1e5..4695ed8 100644
Binary files a/public/tile-map.png and b/public/tile-map.png differ
diff --git a/renderer/Background.ts b/renderer/Background.ts
index 10e7103..00548c4 100644
--- a/renderer/Background.ts
+++ b/renderer/Background.ts
@@ -1,95 +1,89 @@
+import { canvasToImage } from "../lib/canvasToImage";
+import { createCanvas } from "../lib/createCanvas";
+import { ZombieSurvival } from "../simulator";
 import { assets } from "./Assets";
-import { canvasToImage } from "@/lib/canvasToImage";
-import { createCanvas } from "@/lib/createCanvas";
-import { ZombieSurvival } from "@/simulator";
 
-export const BITMASK_TO_TILE_INDEX = {
+export const BITMASK_TO_TILE_INDEX: Record<number, number> = {
   0: 0,
-  4: 1,
-  92: 2,
-  124: 3,
-  116: 4,
-  80: 5,
-  // no index 6: tile not used
-  16: 7,
-  20: 8,
-  87: 9,
-  223: 10,
-  241: 11,
-  21: 12,
-  64: 13,
-  29: 14,
-  117: 15,
-  85: 16,
-  71: 17,
-  221: 18,
-  125: 19,
-  112: 20,
-  31: 21,
-  253: 22,
-  113: 23,
-  28: 24,
-  127: 25,
-  247: 26,
-  209: 27,
-  23: 28,
-  199: 29,
-  213: 30,
-  95: 31,
-  255: 32,
-  245: 33,
-  81: 34,
-  5: 35,
-  84: 36,
-  93: 37,
-  119: 38,
-  215: 39,
-  193: 40,
-  17: 41,
-  // no index 42: tile not used
-  1: 43,
-  7: 44,
-  197: 45,
-  69: 46,
-  68: 47,
-  65: 48,
+  16: 1,
+  88: 2,
+  216: 3,
+  248: 4,
+  120: 5,
+  72: 6,
+  64: 7,
+  208: 8,
+  122: 9,
+  222: 10,
+  255: 11,
+  251: 12,
+  106: 13,
+  82: 14,
+  94: 15,
+  219: 16,
+  254: 17,
+  // 18 not used
+  127: 19,
+  75: 20,
+  210: 21,
+  250: 22,
+  126: 23,
+  31: 24,
+  95: 25,
+  91: 26,
+  74: 27,
+  214: 28,
+  // 29 not used
+  107: 30,
+  80: 31,
+  10: 32,
+  66: 33,
+  2: 34,
+  86: 35,
+  223: 36,
+  123: 37,
+  90: 38,
+  24: 39,
+  218: 40,
+  104: 41,
+  18: 42,
+  30: 43,
+  27: 44,
+  26: 45,
+  8: 46,
+  22: 47,
+  11: 48,
 } as const;
 
 const neighborOffsets = [
+  [-1, -1],
   [0, -1],
   [1, -1],
+  [-1, 0],
   [1, 0],
-  [1, 1],
-  [0, 1],
   [-1, 1],
-  [-1, 0],
-  [-1, -1],
+  [0, 1],
+  [1, 1],
 ] as const;
 
 export function getBitMask(
   map: string[][],
   x: number,
   y: number,
-  outOfBound = 1,
+  outOfBoundToken = " ",
 ) {
-  const width = ZombieSurvival.boardWidth(map);
-  const height = ZombieSurvival.boardHeight(map);
-
   let bitmask = 0;
 
   for (let i = 0; i < neighborOffsets.length; i++) {
     const [dx, dy] = neighborOffsets[i];
-    const nx = x + dx;
-    const ny = y + dy;
+    const token = map[y + dy]?.[x + dx] ?? outOfBoundToken;
 
-    if (ny < 0 || ny >= height || nx < 0 || nx >= width) {
-      bitmask |= outOfBound << i;
-    } else if (map[ny][nx] === "R") {
+    if (token === "R") {
       bitmask |= 1 << i;
     }
   }
 
-  return bitmask as keyof typeof BITMASK_TO_TILE_INDEX;
+  return bitmask;
 }
 
 export async function generateBg(