private void PictureBoxTilesetMouseDown(object sender, MouseEventArgs e)
{
_mouseDown = true;
ResetPoints();
if (_originPoint.X < 0 && _originPoint.Y < 0)
{
_originPoint.X = _endPoint.X = e.X;
_originPoint.Y = _endPoint.Y = e.Y;
_selectionActive = true;
RefreshSelection();
}
}