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image/gif: bounds offset reversed when encoding #30887
Description
go 1.12.1 linux/amd64
What did you expect to see?
image shift not depending on saved format.
What did you see instead?
gif image shifted in the opposite direction to all other formats.
(several other image format generating libs tried and gif the only one in disagreement.)
demo example:
package main
import "image"
import "image/png"
import "image/jpeg"
import "image/gif"
import "os"
type offsetImage struct{
image.Image
Rect image.Rectangle
}
func (i offsetImage) Bounds() image.Rectangle{
return i.Rect
}
func main() {
img:=offsetImage{image.Rect(0,0,50,50),image.Rect(0,0,50,50) }
w,_:= os.Create("1.png")
png.Encode(w,img)
w,_= os.Create("1.jpg")
jpeg.Encode(w,img,nil)
w,_= os.Create("1.gif")
gif.Encode(w,img,nil)
img.Rect=image.Rect(30,30,80,80) // same size just offset
w,_= os.Create("2.png")
png.Encode(w,img)
w,_= os.Create("2.jpg")
jpeg.Encode(w,img,nil)
w,_= os.Create("2.gif")
gif.Encode(w,img,nil)
}
output
without shift:all white, all the same as expected
with shift:
(png image above not showing in github md?)
Activity
katiehockman commentedon Mar 19, 2019
I was able to reproduce this, does seem that gif changes after the offset in a way that's different from the other image formats.
/cc @nigeltao for image/gif package
gopherbot commentedon Mar 21, 2019
Change https://golang.org/cl/168418 mentions this issue:
image/gif: don't assume Encode src's origin is (0, 0)splace commentedon Mar 21, 2019
confirmed fixed. (with patch) demo now results in matching images and original code now works as expected. nice.
image/gif: don't assume Encode src's origin is (0, 0)