IgorB:
Thanks for the photomontage.  That makes it real easy for GG to implement.  He added the textbox and clear button and used your suggested "mask-like" layout.
When there is a slider, I think would be fine to have a textbox and its
Clear button to clear the slider. So I have done two quickly
photomontage, a simply and another inhereited by Mask tool.
A Ubuntu16 build is at:
   https://www.cinelerra-gg.org/download/testing/cinelerra-5.1-ub16-x86_64-static.txz

Off topic.  Andrea's suggestion for changing the Projector and Camera menus to be mask-like also is a good idea.  I am not sure if there are BT issues related to Projector/Camera but it would probably be best to do that at the same time as other work on these 2 as that is easier for GG in case the layout has any new features.  Again, at that time if someone provides a layout, then GG will implement it as he does not like to design it himself.  gg/Phyllis