Chess changes: en passant and not suggesting illiegal moves

[Tyson Williams]

Thanks Johnny,

If the move suggestions are an easy fix for you, then by all means, go
ahead.  I will put it on my TODO list a well.  My typical development
environment includes C# or F#, Visual Studio, and Azure DevOps or GitHub,
so the different environment will be a challenge, but I am willing to try.
Your links into the code will be very helpful.

On Sun, Jun 7, 2020, 5:20 AM Johnny Jazeix <jazeix at gmail.com> wrote:

> Hi,
>
> I removed the images from your mail, created a bug on our tracker
> (https://phabricator.kde.org/T13248) and added the images in it
> https://phabricator.kde.org/M175.
> For the en-passant move, I probably won't have the knowledge to fix it
> quickly.
>
> For restraining the moves to the only "really" possible ones, it
> should be possible:
>
> https://invent.kde.org/education/gcompris/-/blob/master/src/activities/chess/chess.js#L317
> :
> we display the possible moves.
> Here is the function where we check if the move is legal or not:
>
> https://invent.kde.org/education/gcompris/-/blob/master/src/activities/chess/chess.js#L151
>
> I can add it in my todo list, except if you want to take a look.
>
> Johnny
>
> Le dim. 7 juin 2020 à 03:30, Tyson Williams <tyson.d.w at gmail.com> a écrit
> :
> >
> > Hello everyone,
> >
> > I decided to only take screenshots for the incorrect cases, of which
> there are five.
> >
> > The first is that en passant is not possible but should be.  See
> attached file "en_passant.png".
> >
> > The other four cases are moves that are suggested but should NOT be.  In
> all four cases, only the suggestions are wrong.  Trying to play at any of
> these "bad" suggestions displays the error message "Invalid, your king may
> be in check".
> > 1. Suggested moves for the king should not include moving to a square
> that is under attack.  In the attached file
> "1-King_moving_into_an_attack.png", there should be no suggested moves for
> the king.
> > 2. When in an absolute pin, there should be no move suggestions.  In the
> attached file "2-Stuck_in_absolute_pin.png", there should be no suggested
> moves for the bishop.  There are some other pin-related cases that are more
> complicated.
> > 3&4. When in check, the only valid moves of non-king pieces are to block
> or capture.  In the attached file "3_Only_move_absolute_pin.png", the only
> suggested move should be to block the queen's attack.  In the attached file
> "4-Only_move_capture.png", the only suggested move should be to capture the
> queen.
> >
> > The program already knows that some of the suggestions are no good.
> That is why it doesn't allow those moves and shows an error message
> instead.  I just want it to never show those bad suggestions in the first
> place.
> >
> > On Fri, Jun 5, 2020 at 5:35 PM Tyson Williams <tyson.d.w at gmail.com>
> wrote:
> >>
> >> Hello Johnny,
> >>
> >> Thanks for the links.  I will take a look at them.
> >>
> >> To help you and others better understand the cases, it just occurred to
> me that I could create and markup some screenshots.  I should be able to
> get those over the weekend.
> >>
> >>
> >> On Fri, Jun 5, 2020, 2:48 PM Johnny Jazeix <jazeix at gmail.com> wrote:
> >>>
> >>> Hi Tyson,
> >>>
> >>> thank you for your explanation. We are using the engine of p4wn
> >>> (https://github.com/douglasbagnall/p4wn) to power the chess activity.
> >>> There were already a few bug they fixed for "en passant":
> >>> https://github.com/douglasbagnall/p4wn/issues?q=is%3Aissue+is%3Aclosed
> >>> but maybe that did not handle all the cases.
> >>>
> >>> If you have knowledge, for sure these improvements are welcome!
> >>> If you can reproduce the bugs in http://p4wn.sourceforge.net/, then it
> >>> would be better if this can be fixed upstream (proposing a pull
> >>> request) and we'll have to report on our code
> >>> (
> https://github.com/gcompris/GCompris-qt/blob/master/src/activities/chess/engine.js
> ).
> >>> I can help you understand the code on GCompris, but will have more
> >>> difficulty to help on the engine.
> >>>
> >>> I'll take a closer look tomorrow to try to understand more the
> >>> different use cases you are talking about.
> >>>
> >>> Johnny
> >>>
> >>> Le ven. 5 juin 2020 à 14:18, Tyson Williams <tyson.d.w at gmail.com> a
> écrit :
> >>> >
> >>> > !Hello everyone,
> >>> >
> >>> > My children (twin 6yos and 4yo) love playing the activities in
> GCompris.  In particular, one of my 6yos especially enjoys that he can been
> me at the flying kings variant of checkers.
> >>> >
> >>> > Anyway, there are two improvements that I would like to make to the
> chess activities.
> >>> >
> >>> > The first is that en passant is not a supported move.  I would like
> to add support for them.
> >>> >
> >>> > The second is about the inconsistency in which moves are displayed
> as possible.  After clicking on a piece, the general behavior is that the
> squares to which that piece can move are highlighted.  The suggested moves
> vary according to the situation in many cases.
> >>> >
> >>> > Here are five cases in which only legal moves are suggested:
> >>> > - Opponent pieces in the way (e.g. if R on a1 can capture at a2,
> then capturing at a3 is not suggested)
> >>> > - Own piece in the way (e.g. there are no suggested moves for the
> king as the first move of the game)
> >>> > - Pawn's first vs non-first move (i.e. only when it is a pawn's
> first move and the two squares in front of it are empty is the suggestion
> given to move the pawn forward two squares)
> >>> > - Pawn capture (i.e. only if an enemy piece is diagonally in front
> of a pawn is the suggestion given to move in that diagonal direction)
> >>> > - Castling (i.e. castling the king by moving it horizontally is only
> suggested if it is valid...which means the king has never moved, the rook
> as never moved, square the king moves through is not being attached, and
> the square the king stops on is not being attached)
> >>> >
> >>> > In contrast, there is one case in which invalid moves are suggested,
> which is when the king of that player would become under attack (except for
> castling as mentioned above).  I know of four ways in which this can happen:
> >>> > - Suggestions are given to move the king to a square that is under
> attack.
> >>> > - Suggestions are given to move a piece that is absolutely pinned.
> >>> > - For a piece that can put itself into an absolute pin, suggestions
> are given to move that piece that would not place it into an absolute pin.
> >>> > - For a piece that can capture a piece attacking the king, suggests
> are given to move that piece that does not capture that piece or place it
> into an absolute pin.
> >>> >
> >>> > If the user clicks such an illegal suggestion, the follow message is
> displayed.
> >>> > > "Invalid, your king may be in check"
> >>> >
> >>> > This message makes me think that I have missed some case....that the
> game can suggest a move that is illegal for some reason other than the king
> being under attack after the move.  However, I have been unable to find
> such a case.
> >>> >
> >>> > When my children play chess and their king becomes checked, they
> click the suggested moves to get out of check, but many of them are illegal
> and display that message to them.  I would prefer if those illegal moves
> were not suggested.
> >>> >
> >>> > Would making en passant possible and removing illegal move
> suggestions be welcome changes to the chess activities?
> >>> >
> >>> > --
> >>> > Tyson Williams
> >
> >
> >
> > --
> > Tyson Williams
>
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