image/gif: EncodeAll fails to allow non looping animated gif #15768
Comments
ghost
changed the title
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@chriwup I believe what you want to do is set the loop count to 1 and not -1. IMO -1 doesn't make sense for a loop count to mean no loop. I have a small script that you can use to play around with the loop count values here https://play.golang.org/p/zIPjxYjuCV and using 1 should cut the deal. Here is the code below inlined package main
import (
"flag"
"fmt"
"image/gif"
"net/http"
"os"
)
func exitIfError(err error) {
if err == nil {
return
}
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
func main() {
gifURL := flag.String("url", "https://brobible.files.wordpress.com/2016/03/joker1.gif", "the URL of the GIF")
loopCount := flag.Int("loop-count", 1, "the max loop count of the GIF")
flag.Parse()
res, err := http.Get(*gifURL)
exitIfError(err)
gifImg, err := gif.DecodeAll(res.Body)
_ = res.Body.Close()
exitIfError(err)
gifImg.LoopCount = *loopCount
_ = gif.EncodeAll(os.Stdout, gifImg)
}$ go run gif-loop-count.go --url https://j.gifs.com/Z6ozLJ.gif --loop-count 2 > lc2.gif # Make it loop twice
$ go run gif-loop-count.go --loop-count 1 > lc1.gif # Should loop only once.Let me know what you think. |
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Actually I stand corrected, loop=1 sets it to loop once which is not what you want. Your original issue still stands, I've also corrected my script to include |
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Yeah, it's unfortunate that, in the underlying "Netscape Looping Application Extension" format, 0 means loop forever and 1 means loop twice. To loop exactly once, we need to omit the extension entirely. Given the back-compat constraints, I think that "negative means loop exactly once" is the right fix, in Go 1.8. |
quentinmit
added
the
NeedsFix
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Punting to Go 1.9. I started to do this but it seems important to harmonize both Read and Write, and it was not entirely clear to me how to do that. |
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Change https://golang.org/cl/93076 mentions this issue: |
Please answer these questions before submitting your issue. Thanks!
go version)?go version go1.6.2
go env)?darwin/amd64
In package image/gif, I'm trying to use EncodeAll() to create a non-looping animated gif with several frames, but it will always loop. In the GIF specifications
0means forever, so-1should the way to go to disable looping, unfortunately setting this value does not work in go.I should be able to set
LoopCount = -1and my resulting gif should not loop.I want an animated gif, but not a looping animated gif.
My output gif is looping forever (same as LoopCount =
0).The first problem lies in src/image/gif/write.go
This should be removed to allow a negative value.
The second problem is that Netscape Looping extension header is written in the file whenever there are several frames:
I believe this should be changed to:
Another way to fix the problem would be to change the meaning of LoopCount '0' value to actual "no loop", but this could break the expected behaviour for some people. As in other languages, setting
-1sounds ok as long as it's commented somewhere.The text was updated successfully, but these errors were encountered: