private unsafe void ParseExistsTable(byte* flags, int columns, int rows)
{
ExistsTable = new bool[columns, rows];
for (int r = 0; r < rows; r++)
{
for (int c = 0; c < columns; c++)
{
var cur = flags[r*columns + c];
ExistsTable[c, r] = (cur & 15) != 15;
}
}
}