Created attachment 122815 [details]
Image of annotations with and without a drawing tablet.

SUMMARY
Hi, after upgrading my system to Ubuntu 19.04, I experienced an error when using a drawing tablet. The error results in spiky and jagged looking annotations. Okular ran perfectly before I upgraded my system from 18.04 to 19.04. My drawing tablet works perfectly in other drawing applications and its software is up to date. By the sounds of it, this error was caused only when I updated to Ubuntu 19.04 but I'm unsure as to why. I've tried using different versions of Okular and observed the same errors.

STEPS TO REPRODUCE
1. Be using Ubuntu 19.04
2. Select the annotation feature
3. Draw with stylus

OBSERVED RESULT
The annotation made with the drawing tablet has spiky and jagged edges.

EXPECTED RESULT
The annotation should appear similar to a mouse annotation and less spiky and jagged.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
In the provided attachment, is a picture of what the annotation looks like with both the drawing pad and a mouse. The first one (marked as number 1) is done with a drawing pad. The second one (marked as number 2) is done with a mouse.