For the float window, implement a row of buttons that actuates the modifer keys and holds them until another interaction has occurred in the target window (e.g. mouse click).
Use case example: In Affinity Photo, to set the source of the clone stamp tool, one has to hold shift and then click onto the area that shall be used as the source for cloning.
For the float window, implement a row of buttons that actuates the modifer keys and holds them until another interaction has occurred in the target window (e.g. mouse click).
Use case example: In Affinity Photo, to set the source of the clone stamp tool, one has to hold shift and then click onto the area that shall be used as the source for cloning.