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2020-12-13 12:00 nesdori  
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there's a minor layout error. the firefly should initially face up instead of right. of course the next step will be in either case that firefly moves to the right so there's no real difference other than perfect accuracy to the original :)  
  
the c64 bd1 has different internal direction implementation for fireflies and butterflies. for fireflies the directions are:  
  
00: lefT  
01: up  
10: right  
11: down  
  
and for butterflies:  
  
00: down  
01: left  
10: up  
11: right  
  
bdcff-format always uses the firefly format for fly directions (because it's the atari format for both flies) and so c64 .bd files have incorrect initial directions for butterflies and they should be adjusted based on the table above.  
  
the c64 bd1.bd file indeed for this cave says:  
  
Point=10 10 BUTTERFLYr  
  
so the initial direction is "right "but it must be converted using the above table and it change§s to "up".  
  
the same goes for example caves d and m. the c64 bdcff says that butterflies are facing left although they should be facing down which is the default initial direction for butterflies.  
  
the atari bd1.bd has these correct:  
  
int 1:  
Point=10 10 BUTTERFLYu (up)  
  
cave d:  
Point=10 9 BUTTERFLYd (down)  
  
so it's more safe to use the atari bdcff to check initial fly directions because no conversions needed there. atari fly direction implementation is same for both flies. there's no difference between c64 and atari caves however. it's just that the c64 direction implementation fools bdcff-format.  
  
cave d and m butterfly directions are correct (down) so  dustin , i think you didn't use the c64 .bd to place flies but you somehow put the butterfly incorrectly in this cave, maybe by feel :)

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2020-12-13 12:13 nesdori  
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and of course, this is not really a bdcff problem but a bug in programs which produce bdcff files from c64 cave data. but it's dangerous to fix this for c64.bd files because then you can't be sure whether a bdcff file is produced with buggy or fixed implementation :)

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2020-12-13 12:16 dustin  
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thx  nesdori ! i won't change it, as it does not affect the visible cave effects at all. and changing it would now change the order of the caves, so it's not worth it here imo ;)  
  
in fact, i did it based on gdash. but now i see that gdash also has an up-facing butterfly, so indeed, it must have been by feel :D  
  
i'm warned; i'll check the initial directions more carefully in bd2+3!