isCellDirty method
Implementation
bool isCellDirty(int x, int y) {
if (x < 0 || y < 0 || y >= dirtyBits.length) return false;
final bits = dirtyBits[y];
if (bits.isEmpty) return false;
final word = x >> 5;
if (word >= bits.length) return false;
final mask = 1 << (x & 31);
return (bits[word] & mask) != 0;
}