fix: slice

packages/topdown/src/resources/tiles.js

@@ -138,21 +138,30 @@ export default (latus) => {
       }
     }
 
+    /* eslint-disable no-param-reassign */
     slice([x, y, w, h]) {
+      if (w <= 0 || h <= 0) {
+        return [];
+      }
+      const [fw, fh] = this.size;
+      const n = fw - w;
       const slice = new Array(w * h);
-      let i = y * this.width + x;
+      let i = y * fw + x;
       let j = 0;
       for (let l = 0; l < h; ++l) {
         for (let k = 0; k < w; ++k) {
-          slice[j] = k < 0 || k >= w || l < 0 || l >= h ? 0 : this.data[i];
+          slice[j] = x < 0 || x >= fw || y < 0 || y >= fh ? 0 : this.data[i];
+          x += 1;
           i += 1;
           j += 1;
         }
-        i -= w;
-        i += this.width;
+        x -= w;
+        y += 1;
+        i += n;
       }
       return slice;
     }
+    /* eslint-enable no-param-reassign */
 
     stampAt([x, y, w, h], tiles) {
       if (0 === w || 0 === h || 0 === tiles.length) {