As described in Rex’s own site about GridMove.Direction, this expression is only valid if the movement is to a neighbouring tile. In the Slidewalk system, however, although the construction of the Slidewalk path may be straight, the target tiles may be separated from each other for efficiency sake (ie less node paths to draw in Tiled).
It is inefficient to ‘connect-the-dots’ in C2 by tagging the tiles that the path goes over, so I’m instructing GridMove to move to the Slidewalk target tiles that are not neighbours, This makes GridMove.Direction invalid.
What I did, instead, was to do my own GridMove direction by comparing GridMove’s SourceLX/Y and DestinationLX/Y expression and generate a direction using conditions.
At this point, however, the conditions assume that the nodes are positioned in a way that it follows the lines for 8 directions, as it checks how the target tile’s LX and LY are different for the source’s corresponding LX and LY.