Loop count when exporting GIF about omggif HOT 9 CLOSED

It took me a lot of struggle, but here is how Looping in GIFs work (or at least how browsers interpret it):

• to repeat forever, there should be the Netscape block containing 0
• to repeat just once, there should be no Netscape block
• to repeat N times (1<N), there should be a Netscape block containing N-1

Maybe you could make the "loop" input of GifWriter ("loop" output of GifReader) represent a true number of loops, and read/write it correspondingly? You could keep 0 as Forever.

from omggif.

Just to make sure I understand now, if you set loop to undefined on the GifWriter options, it behaves correctly and plays once? If you set loop to 3 it loops 4 times?

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I know it's a little inconvenient, but my intention with the library was to be as low level on top of the GIF format as possible, meaning it basically just handles writing out the format and doing the compression, but not much else, and gives the user fairly direct control over the output of the GIF file, etc. I think the first thing is just to document this clearly. Then I would still like loop to mean "this is the value that gets written into the GIF file", but there could definitely be an additional helper function like gifLoopValueToActualPlayCount (okay needs a better name) that will return the proper loop value (including returning undefined/null for no block) for the actual number of times you want it to play, and the reverse calculation for reading.

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Ok, I understand. But I just expected the "loop" property be the number of times the GIF repeats.

I could not find how this property works anywhere on the internet, so I discovered it by testing.

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I think it's a manner of terminology. "loop" is the process of restarting to the beginning after hitting the end, so if something loops once it plays twice. So the play count is not the same as the loop count, the loop count is 1 less than the play count. Again if something "repeats" once it means in total it plays twice (the first one and then the 1 repeat). Does this make sense and match the behaviour you described?

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Thats an interesting theory :D But loop=0 repeats forever .. should not it repeat just once? :D

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Looping was added later (it's an extension block). Without any looping a gif will always play once, so the only question was how many additional times will it play. Therefore instead of adding some additional way of saying loop forever, they just made loop of 0 mean loop forever.

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I understand, that they made it work in a certain way.

I am just saying, that your idea, that they intended to make the loop number correspond to the number of times skipping back, is very unprobable.

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Don't know why you think it is unlikely, I am certain this is how it was designed.

I can't dig up the original Netscape references, but this is from the gifsicle code from the late 90s.

https://www.lcdf.org/gifsicle/man.html

--loopcount[=count]
Set the Netscape loop extension to count. Count is an integer, or forever to loop endlessly. If you supply a --loopcount option without specifying count, Gifsicle will use forever. --no-loopcount (the default) turns off looping. 

Set the loop count to one less than the number of times you want the animation to run. An animation with --no-loopcount will show every frame once; --loopcount=1 will loop once, thus showing every frame twice; and so forth. Note that --loopcount=0 is equivalent to --loopcount=forever, not --no-loopcount. 

"--loopcount=1 will loop once, thus showing every frame twice"

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