behind osgText::Text. I made it so the box would get drawn using
whichever BackdropImplementation was selected. However, I did not
implement STENCIL_BUFFER. In that case it defaults to drawing the
bounding box using POLYGON_OFFSET instead.
Also made it so the BOUNDINGBOX and FILLEDBOUNDINGBOX are drawn with a
settable color and margin size.
While I was at it I tightened up the values applied with DEPTH_RANGE
and POLYGON_OFFSET, not just for drawing the bounding box but also for
drawing backdrop text (these values must be coupled since the bounding
box has to be drawn deeper in Z than the backdrop text). The values
in use before seemed like overkill and I was seeing some z-clipping
with my background scenery in the case of DEPTH_RANGE. If there was a
good reason for the large values please let me know...."
