Created attachment 121356 [details]
Example of transformed layers (lines)

SUMMARY
Only free transform tool works as it should. All other options produce very bad results. Lines of the transformed layer get jigged, pixelated (squarish). It doesn't get better by changing the brush, or working on the higher DPI image...

STEPS TO REPRODUCE
1. Take any layer
2. Try to transform it using any transform tool or brush (except free one)
3. Do it again?

OBSERVED RESULT
badly transformed object 

EXPECTED RESULT
Transformed object, perhaps more blurry but smooth

SOFTWARE/OS VERSIONS
Windows: 7 - ultimate,10 - home
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION