GR.OPTION_FLIP_Y causes weird pixel spacing in drawimage

[jusack]

I encountered a weird bug in JuliaPlots/Plots.jl#4833 which I traced to the yflip parameter. I was able to reproduce it in a MWE using only GR. Do you have any idea, what might be the cause for the observed behavior? I am at version GR v0.72.10 and GR_jll v0.72.10+0

using GR
GR.clearws()
GR.setviewport(0,1,0,1)
GR.setwindow(0,50,0,50)
GR.setscale(GR.OPTION_FLIP_Y) # GR.setscale(0) is fine
GR.drawimage(0,300,300,0,300,300,rand(UInt32,90000))
GR.updatews()

[jheinen]

Could you please explain what the problem is? I tried the following example (with a real image) and could not see any problems:

using GR

w, h, d = readimage("tiger.png")

setviewport(0, 1, 0, 1)
setwindow(0, 50, 0, 50)

setscale(GR.OPTION_FLIP_Y)

drawimage(0, 100, 0, 100, w, h, d)
updatews()

Input image (tiger.png):

Result:

[jusack]

I have posted some images of how it looks in the original issue in Plots linked above. This is the result of the pure GR version:
.
In Plots.jl I observed that it depends on the size of the image that is plotted, if I crop the tiger.png to 300x300 (a size that I observed to show the pixel unevenness strongly)

I can also see the unevenness there: (using your code snippet, shown side by side with MS Paint)

[IngoMeyer441]

@jusack Thanks for pointing us to this bug. We fixed the non-square pixels in C-GR commit b9aefa6, so (currently) you will need to use the latest GR runtime to get the fix.

[jusack]

Awesome, thanks for the quick fix!