There is no documented way to do this. I do not know if there is a way to figure things out at the Java level.
What I ended up having to do was use trial and error to measure the widths of the various forms of decoration. I then wrote my own hgrightsize() routines that figures out the class of graphics element (e.g., text() vs uipanel() vs uicontrol) and dispatches to the appropriate "right sizing" subroutine.
I cannot give you the code, but I can tell you the experimental values for uicontrols, in pixels:
checkbox: 15
edit box: decoration 21 if multiline, 0 for single line
listbox: 19
popup: 16
pushbutton: 0
radiobutton: 15
slider: meaningless to "rightsize" a slider
textbox: 0
togglebutton: 0
There are some complications when you are determining the size of the text area itself via Extent: in some cases you should only look at the first line of a multiline String, and in other cases you need to find the widest line of the multiline string; in some cases the height of your box is one line and in other cases it should be the height of all of the lines. Those factors are easier to determine than the number of pixels of margin to allow for decorations.
