Hi everybody!
I solved a problem when spiral knights run fullscreen, you see only a cropped, windowed and in a corner of the screen.
To solve this:
FOR STEAM USERS (100% working):
1) go to your spiral knights folder (usually located at "C:\Program Files\Steam\steamapps\common\Spiral Knights" )
2) go to the folder "java_vm"
3) go to folder "bin"
4) right click on "java" (the icon with a cup of coffe)
5) go to "compatibility" tab
6) check the "disable display scaling on high DPI settings" option
7) click on "apply" and then "ok"