Comments/Ratings for a Single Item

Why would you take the King off the board for this?

The purpose of the accelerated check test is not only to determine whether the King is in check in the current position, but also to greatly facilitate testing whether the King would get exposed by any of the moves. One contribution to this is to mark every square where the King itself cannot go. The King is taken off to prevent it would block enemy slider moves (or lame leaps), creating the illusion that it would be safe to "step into his own shadow".

The test is NOT done by only processing all pseudo-legal moves. Because that would not reveal which pieces are protected (and thus cannot be captured by the King). For the purpose of knowing where the King could go the move generator should basically work under the fiction that all destinations contain the enemy King. That applies to empty squares as well friendly pieces; these will be marked as inaccessible to the King when the move hitting those is a move that can capture. Even when it cannot capture what is actually there.

The code I use avoids this by trying each pseudo-legal move and checking whether any piece in the new position is checking the King.

That would indeed be an alternative: do a full king-capture test after every King move. But it would be more expensive, as a King usually has several moves. So you would have to do enemy move generation several times. (And who knows how mobile a royal piece can be, in a chess variant?) Testing whether a destination contains the King is not any more expensive than marking the destination. And to do it, you only need to geenrate all enemy moves once. Then for each King moves only have to test whether the destination is marked. And to know whether you are in check it would just have to test whether the square the King is currently on is marked.

But the fiction that every square where you are allowed to capture contains a King should also be applied to locust captures. And this wasn't done.

The accelerated check test would not work in variants where there are multiple absolute royals. (Extinction royaly is no problem; there it just skips the check test completely if there still is more than one royal.)

The issue was that the test for being already in check was done with the King taken off the board

Why would you take the King off the board for this? Couldn't this cause false positives and false negatives from divergent pieces like Pawns or Cannons?

This was a bug that did not yet express itself. A Checker diagonally adjacent to the enemy King would not deliver check if a friendly piece was immediately behind that King, blocking the landing square. But that blocking piece would then essentially be pinned, and its moves should not be highlighted.

The code I use avoids this by trying each pseudo-legal move and checking whether any piece in the new position is checking the King.

So I would suggest a compromise between your quick method and your reliable method. Flag pieces that can capture a piece without moving to its space, and use your reliable method on these while just checking if other pieces can move to the King's space.

I think I managed to even use some acceleration for the pieces that can perform 'locust capture', by avoiding you have to generate all their moves, and just limit it to moves that could potentially hit the King. This would be the move that already delivers check, and the moves that that mutate a square along the path in a way that would allow a slider leg of the locust capture to pass. Which is what was already done for direct captures too.

The issue was that the test for being already in check was done with the King taken off the board, by comparing the destination of capture-capable moves with the King square. But this was tested only on a final leg, and not for a non-final leg, where the capture would be a locust capture, and the piece would move on after it. I now compare the (temporary evacuated) locust square with the king position too, and if it matches make the move go over to the next leg to see if it can be completed. (For an Advancer that would always be possible, but a Long Leaper it might not be.) If the move can be completed, the locust square would be marked as attacked. This will then make the 'check' message appear.

But more importantly, squares on the second leg would also get marked as squares where a check could be discoved. This was a bug that did not yet express itself. A Checker diagonally adjacent to the enemy King would not deliver check if a friendly piece was immediately behind that King, blocking the landing square. But that blocking piece would then essentially be pinned, and its moves should not be highlighted. The accelerated test would only have noticed that if the second leg of the Checker capture would have added that Checker capture to the moves affected by mutation (= evacuation) of that landing square.

The reliable method would try out all pseudo-legal moves, and then generate opponent moves in each of the resulting positions, to see if any of those captures the King. All opponent moves will have to be tried to conclude the move is legal (which usually is the case), and on a large variant this can take very long (to the point where GC aborts the GAME-code execution).

Thanks to GAME Code being an interpreted language written in another interpreted language, it is not as quick at things compiled languages would do more quickly, and it will sometimes exceed the time limit that PHP imposes on script execution. This makes optimizations and short cuts more important, and in hand-written code, I have done this. See my previous comment about how I handled the spotting of check in Ultima as an example.

In automatically-generated code, it might be harder to get in the optimizations needed for particular games. So I would suggest a compromise between your quick method and your reliable method. Flag pieces that can capture a piece without moving to its space, and use your reliable method on these while just checking if other pieces can move to the King's space.

OK, I see. The betza.txt code actually does say 'check'. Problem was that by searching for 'say check' I did not find that, because there are quotes around the word 'check'.

It appears that it would only ever say 'check!' when the preset is using the accelerated method for testing legality of highlighted moves. This is the default method, because it is faster. But it is not entirely reliable. The reliable method would try out all pseudo-legal moves, and then generate opponent moves in each of the resulting positions, to see if any of those captures the King. All opponent moves will have to be tried to conclude the move is legal (which usually is the case), and on a large variant this can take very long (to the point where GC aborts the GAME-code execution). And in that branch of teh code it would never say 'check!'.

In the accelerated test it would generate the opponent moves not after the move that has to be tested for legality, but before it. (Meaning that it has to do it only once.) If any of those hit the King, the move that was just made apparently delivers check. After a move considered for highlighting it then only retries such an existing checking move, to see if the check was resolved, and all moves that hit squares mutated by the move-to-be-highlighted (which could have been discovered, and now hit the King). That is a huge time saver.

Where it goes wrong is that during this accelerated check test it actually removes the King, and tests whether it was in check by testing whether a move that hits the square it was on is capture capable. This to avoid a slider check is blocked by the King, making the square behind it to be safe to move to. King moves can then be tested for legality simply by testing whether their destination was marked as attacked. But this procedure does not mark squares that are attacked by locust capture. Such as an Advancer does.

You did not get the point. Does the preset say 'check' when you check with any other piece than an Advancer? I think it doesn't. So then this has nothing to do with the piece being an Advancer.

I dug back into this thread to find the preset he was talking about. He linked to a particular game in which neither Advancer checked the opponent's King. Continuing this game by choosing Annotate and then Move, I played some moves to get a White Flying Dragon to check the Black King, and when I did, it said "check!". After moving the King out of check, I tried to move White's Advancer, but no legal moves are being highlighted on the board for it. However, its legal moves do show up in the Moves field, and when I tried one, it worked. At the top of the Moves field, I see the legal move "A e1-#to; A #to-b1". I think this is not a properly formatted move, and it may be interfering with the ability to recognize the Advancer's legal moves. Also, when I entered it, it did not recognize it as legal, and it gave the error message "#to is not a valid square".

Here are the moves to the position in question so that you can see what's going on.

1. P f2-f5 
1... p f9-f6 
2. P e2-e4 
2... p e9-e7 
3. F i1-h3 
3... f i10-h8 
4. P i2-i3 
4... p d9-d8 
5. B h1-i2 
5... c g10-f7 
6. C d1-f3 
6... f b10-c8 
7. C g1-e3 
7... c d10-f8 
8. K f1-i1 
8... p g9-g7 
9. P b2-b3 
9... c f8-e5 
10. P d2-d4 
10... c e5-f8 
11. B c1-b2 
11... a e10-h7 
12. F b1-e2 
12... p i9-i8 
13. P g2-g5 
13... c f7-e8 
14. P g5-g6 
14... a h7-f9 
15. P c2-c4 
15... p b9-b6 
16. F h3-g2 
16... c e8-d7 
17. P d4-d5 
17... f c8-d6 
18. F e2-h3 
18... p c9-c7 
19. C f3-e6 
19... c d7-e6 
20. P d5-e6 
20... p j9-j8 
21. B b2-a3 
21... b c10-a8 
22. B a3-d6 
22... p e7-d6 
23. R h1-f1 
23... p j8-j7 
24. F g2-d3 
24... b h10-j8 
25. C e3-g1 
25... f h8-i6 
26. P j2-j3 
26... p d8-d7 
27. P a2-a5 
27... p b6-a5 
28. R a1-a5 
28... b a8-b9 
29. P e6-d7 
29... f9-e8;@-d7 
30. C g1-a7 
30... f i6-h4 
31. C a7-d8 // - check! -
31... k f10-f9

Just click on Annotate for Butterfly Chess and paste these in to see the same position.

You did not get the point. Does the preset say 'check' when you check with any other piece than an Advancer? I think it doesn't. So then this has nothing to do with the piece being an Advancer.

By default the preset would apply the checking rule, so moves that leave your royal exposed will be refused. To switch that off (for variants where King capture is a goal) you would have to add an extra line on GAME code to the Pre-Game section. (As the Interactive Diagram does not distinguish thuse cases, but simply allows you to play on in checkmated positions.) The preset enforces the rules. It does not generate conversation during the game.

Yes, I originally would have thought when an Advancer made a move that threatened a King, an enforcing preset would automatically announce check.

However, maybe the Advancer, being an Ultima-like piece, does not actually make a check in an Ultima-like game (which Butterfly Chess is not)?

So I now ask, is that the usual assumption that Applet generated preset code makes for every CV put through the generating process?

I don't know how a generated preset works, but the checked subroutine I use in the fairychess include file normally checks for captures by displacement by checking if each enemy piece on the board can move to the King's position. This would not normally work with Ultima pieces, which do not normally capture by displacement, but I have managed to use this subroutine with Ultima without modifying it. First, let's look at the subroutine:

sub checked king:
    my from piece;
    local movetype;

    set movetype CHECK;
    if isupper cond empty var king $moved space var king:
        def enemies onlylower;
    else:
        def enemies onlyupper;
    endif;
    for (from piece) fn enemies:
        if fn const alias #piece #from var king:
            return #from;
        endif;
    next;
    return false;
endsub;

The key to working with Ultima is that it sets movetype to CHECK. With this in mind, I have written functions for Ultima pieces like this:

def Black_Withdrawer fn join "Black_Withdrawer_" var movetype #0 #1;

Depending upon the value of movetype, it will call either Black_Withdrawer_MOVE or Black_Withdrawer_CHECK, which I have defined separately and differently. Thanks to setting movetype to CHECK, the checked subroutine will use the *_CHECK functions for Ultima pieces. Instead of going through a normal move, one of these functions will check whether the piece at the first coordinate can capture the piece at the second. For example:

def Black_Withdrawer_CHECK 
empty where #frm - file #frm file #to - rank #frm rank #to
and == distance #frm #to 1
and not near #frm I 1
=frm =to;

This first makes sure that the piece is not next to a White Immobilizer (designated as I). It then verifies that the two spaces are adjacent. Calculating the direction away from the piece at #to, it checks whether there is an adjacent empty space in that direction. If there is, it returns true.

@ H.G.:

Yes, I originally would have thought when an Advancer made a move that threatened a King, an enforcing preset would automatically announce check.

However, maybe the Advancer, being an Ultima-like piece, does not actually make a check in an Ultima-like game (which Butterfly Chess is not)? So I now ask, is that the usual assumption that Applet generated preset code makes for every CV put through the generating process? If so, maybe an option can be added to the Applet to ask if Ultima-like pieces should announce check.

A problem for Butterfly Chess, anyway, is that if check is not announced for Advancers, what happens if the opponent's next move leaves his king vulnerable to capture by the Advancer. Does the preset announce the opponent made an illegal move (my much preferred choice, implicit in Butterfly Chess rules), or can the king be captured (if so, is a win announced, or does a player type in 'won' after his K-capturing Advancer move is manually entered, or does he tell his opponent to make a legal move instead)?

Yes, I had seen it, but had no time to look into it yet.

Quickly glancing at the code in betza.txt suggests that it would never say 'check'; searching for "say Check" only finds "say Checkmate" where it terminates a game, as one of the possible reasons for termination. So I would be surprised if you had ever seen it say 'check'.

Is it supposed to say 'check'?

@ H.G. Muller:

Have you seen my comment to you that I am replying to? Not too much of a rush, if you're busy or stumped.

@ H.G.:

In the following link to a Butterfly Chess log, I tried to move my White Advancer from e1 to j6. The (Applet generated) preset allows the move, but does not announce check. Is there a bug here?

https://www.chessvariants.com/play/pbm/play.php?game=Butterfly+Chess&log=panther-joejoyce-2024-10-868

There is only 1 game, not 2. I have modified my comment.

(The 2nd game I have removed was in fact that game interrupted by HG's mistake. That log stayed as a drawn after your attempt to restaure it (but it was impossible to re-start it), and for a reason I ignore, it turned as a victory for Paul "on time". As we had re-started this game from the beginning, I have erased that first log.)

So, the suspect game that has been finished "on time" is a game of Macrochess that I would have won against Richard Milner of time, which is strange because we were playing several moves a day.

I found only one game of yours that ended in the past week, and it ended in checkmate. Were the other games private? Or did they end over a week ago?

It is strange. I was looking for some recent games I was playing and that are not shown anymore in the table of my going games. It appears that they have been finished by time limit. One that I won.

Hmm, strange, in all games I played we always had few days of remaining time. Something has happened I think.

My regrets for my opponent (Richard Milner), this was not intentional.

The log:

timurthelenk-cvgameroom-2024-40-404

Could you add the missing bnespearman to alfaeriePNG?

OK, done.

Could you add the missing bnespearman to alfaeriePNG?

So, I'm thinking that having varying alpha values is available only in true color images, and that provides a reason for keeping these as true color images.

I am not really into these graphics formats, but I can imagine that the palette for historic reasons contains only up to 256 24-bit colors (i.e. RGB without alpha). I guess that with an alpha channel the number of different RGBA combinations in a typical image becomes so large that 256 would almost never be enough, so that no one bothered to define a standard for palette with alpha channel.

I think the trick to making them appear smooth is having edge pixels with varying alpha values. The images I produced had fully opaque edge pixels. As a test, I made a palette version of bknight.png in Ultimate Paint. When I loaded the palette version, the edge pixels no longer had varying alpha values. As a second test, I saved a 24 bit true color version, and it also had lost the varying alpha values on edge pixels. Finally, I saved a 32 bit true color version, and when I reloaded it, it retained the varying alpha values. I also tried the latest version of Paint.net. When I selected the option to save it with an 8-bit depth, it offered the option to set the Transparency threshold, and it said "Pixels with an alpha value lower than the threshold will be fully transparent." So, I'm thinking that having varying alpha values is available only in true color images, and that provides a reason for keeping these as true color images.

I have rendered all images in the alferieSVG directory now as 50x50 PNG using fen2.php?s=50&p=..., in the directory /graphics.dir/alfaeriePNG50. They look like this

(The shell script I used for this is /graphics.dir/alfaeriePNG50/x, and then y to give them the desired filename.)

Since Game Courier is able to copy an SVG to a GD image that will be saved as a PNG, I should be able to modify showpiece.php for conversion from SVG to PNG.

Since I already have a PHP function called imagecreatefromimagick2, the conversion from SVG to PNG was easily handled. However, the results I'm getting do not appear as smooth as the results Greg got.

Here are some examples of what I am getting:

And here are the same pieces as Greg has already converted them:

I have been altering imagecreatefromimagick2 to try to get better results, but so far nothing has worked.

Almost all PNG images are 48x48, though. Only a few that I recently made (mostly compounds done by fen2.php) are 50x50. I produced many of the SVG from which these are derived, but I think Greg had a script that he used to 'bulk convert' the SVG to PNG. He must have used 48x48 in this script. Why he picked that size is unclear to me, as amongst the GIF images it is virtually non-existent.

Maybe he was considering that Game Courier highlights spaces with image borders and wanted to leave some space for the border. However, the borders used are larger than one pixel in width, and the Square Table method will now keep borders from growing too large by reducing the dimensions of the image, whereas the CSS method puts borders around an empty space of a fixed size. So, even if making the images smaller than 50x50 once had some utility, it no longer does.

Should I try to re-render all the alfaeriePNG at 50x50? I suppose I could make my own script for that, at least for everything that we have as SVG, and not compound or post-edited (to apply crosses and such).

Since Game Courier is able to copy an SVG to a GD image that will be saved as a PNG, I should be able to modify showpiece.php for conversion from SVG to PNG. Then I could make sure that the PNG is also a palette image with green for the transparent color.

It appears almost all alfaerie GIF images are 50x50. Some (including the orthodox pieces) are 49x49. Elephants and their derivatives are even 53x50. I recall that I had once seen a 48x48 GIF too, but forgot which that was.

Almost all PNG images are 48x48, though. Only a few that I recently made (mostly compounds done by fen2.php) are 50x50. I produced many of the SVG from which these are derived, but I think Greg had a script that he used to 'bulk convert' the SVG to PNG. He must have used 48x48 in this script. Why he picked that size is unclear to me, as amongst the GIF images it is virtually non-existent.

I think it is undesirable that GIF and PNG images have different sizes. It should be our long-term goal to upgrade all images to the (anti-aliased) PNG, and having different sizes would obstruct that.

So what to do? Should I try to re-render all the alfaeriePNG at 50x50? I suppose I could make my own script for that, at least for everything that we have as SVG, and not compound or post-edited (to apply crosses and such)..

I have no idea how some (mainly of the orthodox pieces) came to be 48x48 or 49x49.

The original Alfaerie pieces were 49x49, because David Howe originally made them for Zillions-of-Games, whose boards were using 49x49 squares. While I made pieces whose dimensions matched the dimensions of the visible image, he made pieces of uniform dimensions that perfectly fit the spaces they were intended for.