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H. G. Muller wrote on Fri, Jul 12 08:45 PM UTC in reply to A. M. DeWitt from 06:37 PM:

It would be nice if we could add a gray highlight for the illegal Lion trading moves for the Chu diagram on this page, but I am not sure how to go about doing that.

If it was easy I would already have done it...

The AI already pays attention to the Lion-capture rules and other legality issues, so the easiest way is to reuse the AI components. When using the NewClick() move entry routine the entered moves are already performed by the same routine NewMakeMove() as that the AI uses.

The AI uses a recursive routine Search(), which uses the move generator GenAll() to create a move list for the side that is on move. It then loops through the moves in that list to find the best/a satifactory one. To do that it first evaluates the direct gain of the move, through a routine ScoreMove(). This calculates the value of what the moves captures, checks if it destroys opponent or own royalty, and adds some info to the move that was not in the 'raw' moves coming from the move generator. (Such as identifying pieces that have to be burned, and remembering the original occupants of mutated squares, identifying the pieces that are made temporary royal or iron by the move and adapt the score for moves that capture those.) After 'cooking' the move with ScoreMove() it can be applied to the current position by NewMakeMove(), and later taken back with UnMake();

Both GenAll() and ScoreMove() make use of the preceding ply, e.g. to generate e.p. captures, and applying trading restrictions.

Currently NewClick() uses GenAll() to create the list of pseudo-legal moves, and then uses mouse clicks to eliminate those from the list that would not be indicated by those, until a single move is left. This raw move is then cooked by ScoreMove(), and performed by NewMakeMove(). As long as there are still multiple moves in the list, the squares corresponding to the next click these need to be selected will be highlighted.

To do fully legal highlighting we would have to make every move, and then judge the position based on the possible replies in the resulting position. Not just the one that is finally selected. That means that ScoreMove() will have to be applied to each of the moves. So the call to it should be moved to within the loop that selects the moves to be highlighted. And then there should be a NewMakeMove(), GenAll(), {judge}, UnMake() sequence in that loop as well, where the 'judge' part would apply ScoreMove() to all replies, to see if there is an instant win amongst those (which then would make the move to be highlighted illegal). If there is the grey cross should be chosen as highlight marker.


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