UMassEdit gui - just one slider mode

Very often I would just like to set an argument of a bunch of units to the same value. Selecting them in the score and opening the edit window I have to set two values in the range slider. It would be useful to have a button to in the gui where it would switch from range slider to just one slider (for instance taking the value of the first unit) and from then on moving the slider would set all the units to the value.

I think this could be done just in the GUI. Have a button which removes the range slider and puts a normal slider and then moving the slider actually actually sets an array of values instead of single value. With the flowlayout stuff, I wonder how does one show and hide the range slider and single slider ? Put them both inside a composite view using absolute coordinates at 0@0 (the composite gets flowed) and then hide an unhide each one in alternate ?

Start by locating the UMassEdit GUI's range-slider and selected-unit editing flow. Inspect how FlowLayout and composite views can show or hide the range and single sliders; done means a toggle switches modes and moving the single slider applies one value to all selected units.