Hello,
G’MIC 3.4.1 half preview window left or right shows only to half top right, which either duplicate left, forward vertical.
Video of the effect (checkered works fine though)
Newly compiled G’MIC 3.4.1 for GIMP (gmic_gimp_qt)
Same problem with G’MIC stand alone (gmic_qt) but with a bigger/higher preview but not full vertical
Video of the effect
Looks like a bug, indeed !
Thanks for your report 
Hello @PixLab ,
The bug should have been fixed with:
You may want to compile the corrected version, from this .tar.gz source file : https://gmic.eu/files/prerelease/gmic_prerelease.tar.gz
(works as 3.4.1, but it’s a pre-version numbered 3.4.2 instead).
Let me know if you succeed to compile the plug-in and if the fix works for you !
@David_Tschumperle yes, compiled without problem, no more bugs on both the GIMP’s plugin and the G’MIC stand alone
in GIMP
Stand alone
Thank you very much
Please have a fantastic day
