🐛 Fix particles being moved twice

src/simulation/update.ts

@@ -69,7 +69,7 @@ export function update(
             }
 
             if (
-                hasMoved(target.get(x, y + 1)) || hasMoved(target.get(x, y + 2))
+                hasMoved(target.get(x, y + 1)) // || hasMoved(target.get(x, y + 2))
             ) {
                 const left = isEmpty(target.get(x - 1, y + 1));
                 const right = isEmpty(target.get(x + 1, y + 1));
@@ -90,10 +90,10 @@ export function update(
         if (isSand(target.get(x, y - 1))) {
             swap(target, x, y, x, y - 1);
             swapped.push([x, y - 1]);
-        } else if (isSand(target.get(x - 1, y - 1))) {
+        } else if (isSand(target.get(x - 1, y - 1)) && !hasMoved(target.get(x - 1, y - 1))) {
             swap(target, x, y, x - 1, y - 1);
             swapped.push([x - 1, y - 1]);
-        } else if (isSand(target.get(x + 1, y - 1))) {
+        } else if (isSand(target.get(x + 1, y - 1)) && !hasMoved(target.get(x + 1, y - 1))) {
             swap(target, x, y, x + 1, y - 1);
             swapped.push([x + 1, y - 1]);
         }