Note that I don't want to generate all moves. Just all moves of one piece. But for that I have to know which piece, and where it starts.
You can get that information yourself. Just play each move under program control, then store the information after each move. Alternately, you can evaluate a move before making it, and the information you need to evaluate it will be on the board.
Even with a comparatively simple piece like the Sissa, a move from e4 to g4 could have gone through e5-e6-f5, f5-g6-g5, e3-e2-f3 or f3-g2-g3.
A Sissa is not a good example in support of what you want to do. All a Sissa function has to do is determine whether there is a path it may legally take to its destination. This can be done without calculating all possible moves for that piece. Besides that, the player would just enter the origin and destination of the piece, not the path that it takes. So, generating paths to compare with the move entered by the player wouldn't work.
The point is that a routine to generate all moves (even not just of one piece, but of all pieces) is needed anyway, for the purpose of setlegal.
Because this is used to check for checkmate and stalemate, it has to be run after the move has been played. You're proposing doing it an additional time. Moreover, it doesn't have to generate detailed information about each move. It just has to cover the first move a piece may make in a sequence of moves. When extra moves have to be entered for a piece, the continuemove command can be used, as it is in Extra Move Chess. But this presumes that you are handling moves one-by-one and not letting them play all at once.
You can get that information yourself. Just play each move under program control, then store the information after each move. Alternately, you can evaluate a move before making it, and the information you need to evaluate it will be on the board.
A Sissa is not a good example in support of what you want to do. All a Sissa function has to do is determine whether there is a path it may legally take to its destination. This can be done without calculating all possible moves for that piece. Besides that, the player would just enter the origin and destination of the piece, not the path that it takes. So, generating paths to compare with the move entered by the player wouldn't work.
Because this is used to check for checkmate and stalemate, it has to be run after the move has been played. You're proposing doing it an additional time. Moreover, it doesn't have to generate detailed information about each move. It just has to cover the first move a piece may make in a sequence of moves. When extra moves have to be entered for a piece, the continuemove command can be used, as it is in Extra Move Chess. But this presumes that you are handling moves one-by-one and not letting them play all at once.