[XForms] Is there some way of putting a semi transparent box on an xyplot?

[Bill Unruh]

Is there some way of putting a semi transparent box on top of an xyplot? In
many programs one can select a part of the polt image-- eg for purposes of
exanding the axes so as to include only that part of the image. But I can find
no way of doing that in xforms. Ie, I want to put the mouse on one part of the
image, hold left button down and drag it across the image. This will then
change the shading of that part of the image-- either in a box whose corner is
the place where the mouse was first left clicked to the current location of
the mouse, or even the whole y range with x values greyed from where the mouse
was first clicked to where the left botton was release. But the only thing
which seems to have a "transparent" colour behaviour seems to be the overlay
postioner, which is not sufficient. Is there anything else in xforms which
would allow this behaviour that I have missed? (even something like "Box A
lies on top of box B but is semi transparent so you can see what is
underneath". 
Under "Images" the semitranparent "glass" seems to do something like this but
that would not seem to be applicable to other objects.


Some sort of overlay would parhaps work, but I have no idea how to make the
colour on the overlay a transparent colour.



--
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     address@hidden
Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/