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List:       kde-games-devel
Subject:    Fixes for KPat Forty & Eight patience game
From:       Ian Wadham <iandw.au () gmail ! com>
Date:       2020-07-10 5:38:40
Message-ID: EC2ED8FF-01F6-4FE2-AAE4-53A2F2817C48 () gmail ! com
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Hi guys,

Good news. In brief, I have found two or three causes of the 10 bugs listed in
https://bugs.kde.org/buglist.cgi?quicksearch=kpat%20forty%20eight.

However, I am going to need help from an expert with a knowledge of the KPat code to \
work out the most appropriate patches.

I will also need help to get patches committed, when they are ready, because I do not \
have access to or knowledge of the newer KDE Community repositories and procedures.

The bug list above relates to false positives and negatives from the 48 solver and \
touches on problems with the Autodrop feature. The false reports from the solver were \
easy enough to fix in patsolve/fortyeightsolver.cpp. However, when I tested my fixes, \
I found that the false positive had been fixed but the false negative was still \
there.

The false positive is due to the 48 solver generating an invalid move and using it to \
reach a win, then saying that the game is winnable when it is not. The human player \
cannot win because he/she is not able to make that move, except by using Demo to \
bypass it ;-). Actually the 48 solver generates invalid moves quite often (as shown \
by Hint), but they are not always used or needed in a winning solution.

Forty & Eight is a 2-pack game. False negatives can occur when there are two cards of \
the same suit and rank that can "go out" onto a foundation pile. The 48 solver always \
chooses the card on the left and ignores the other one. Sometimes playing the card on \
the right leads to a win, and the left hand card is a loser or not a good choice.

For example, stack 0 (on the left) may have a 2 of hearts on top and other suits \
beneath, whereas stack 4 may have the 2-3-4 of hearts in sequence and nothing else \
beneath, and then an ace of hearts comes out of the talon (or heap). The solver will \
consider only the 2 on the left to "go out" onto the ace, but the other 2 would \
almost always be the better option because three cards can go out, rather than one, \
and they will leave an empty stack 4 as well. Empty stacks are an advantage in later \
play.

When I had fixed the 48 solver to deliver both cards that can go out, Autodrop kicked \
in (specifically bool DealerScene::drop() in file dealer.cpp) and undid my good work. \
It uses DealerScene::getHints() to get a list of playable moves and selects out those \
that go out to foundation (or target) piles. Trouble is that if there are two cards \
of the same suit and rank in the list, Autodrop always plays the first (leftmost) \
one. It then returns, letting the animation of the move proceed, but when it is \
called back the second card is no longer playable (nor hinted) because the first card \
has taken its spot. In this kind of situation neither card should be autodropped. The \
human player should be left with a choice as to which card to play, unless it does \
not matter (e.g. if each card is the only one in its pile and either can go out \
first).

I have developed a patch to fix DealerScene::drop(). It takes effect only if the \
current game is Forty & Eight, because I am worried about adversely affecting other \
KPat games. I have looked at other multiple-pack games, but Mod3 and Gipsy do not \
seem to use Autodrop. I am not so sure about Spider, but perhaps it also is affected \
by Autodrop grabbing cards too soon.

Unfortunately my patch is rather kludgey. It is also a pity that it cannot get at \
some information known to the 48 solver and passed back to the main KPat solver, \
patsolve/patsolve.cpp, i.e. which possible moves are automatable. If there are two \
cards of the same suit and rank that can go out, the 48 solver flags neither one as \
automatable.

I really need help from a KPat expert to work out what is the best thing to do here.

Cheers,
Ian Wadham.=


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