isDark method
Implementation
bool isDark(int row, int col) {
if (row < 0 || moduleCount <= row) {
throw RangeError.range(row, 0, moduleCount - 1, "row");
}
if (col < 0 || moduleCount <= col) {
throw RangeError.range(col, 0, moduleCount - 1, "col");
}
return _data[row * moduleCount + col] == _pixelDark;
}