Comment # 14 on bug 1100765 from . .

Okay.

Bottom line: File > Create > Screenshot... > Snap does work if compositing is
on.

Command (1) initially showed false. The only way I could find to turn
compositing on the first time was to go to System Settings > Display and Montor
> Compositor and check "Enable compositor on startup". Repeating command (1)
then returned true. Did a screenshot from gimp of another window and it worked.
No error messagebox.

Command (2), to suspend and resume compositing, worked as expected with gimp
and screenshots.

Once compositing was active, command (3) showed the /Screenshot path that was
mentioned in the error message.

Haven't used compositing/Desktop effects in the past. It doesn't seem to make a
difference to Spectacle whether compositing is active or not, just to gimp. 

Starting gimp with dbus-launch also worked without the compositing requirement.

Regarding the 3rd menu option, "Select a region to grab":

- If I start gimp from the menu (compositing on or off), the 3rd menu option IS
NOT there.
- If I start gimp from the command line using dbus-launch (compositing on or
off), the 3rd menu option IS there.


Commands
--------

(1): 
qdbus-qt5 org.kde.KWin /Compositor active 

(2):
qdbus-qt5 org.kde.KWin /Compositor suspend  - gimp screen error
qdbus-qt5 org.kde.KWin /Compositor resume   - gimp screen worked

(3):
qdbus-qt5 org.kde.KWin