To the software designers

[mbp]

Steve,

Thanks for your note about Geomview.

Several thoughts come to my mind in response to your question about
transparency.  First of all, it depends a lot of what kind of machine
you're using.  On an SGI, it is possible to vary the transparency, via
the Materials panel.  Click the "Transpancy" button to turn
transparency on (for the target object), then move the slider to
modify the transparency level.  Note however, that it doesn't really
work correctly.  In order to be correct, Geomview would have to sort
the polygons in your picture in screen-depth order on each redraw,
which it doesn't do.  So sometimes the picture you get with
transparency looks really bad.  Sometimes, however, particularly if
you crank the transparency way up (i.e. almost invisible), it looks
OK.

We haven't yet implemented transparency for the NeXT or X versions of
Geomview.

Another thing you might consider, however, is to display an object in
wire-frame (turn edges on and faces off) to achieve an effect sort of
like transparency.  This works with any version of Geomview, and has
the advantage of speeding up the drawing time as well (it takes lot
less time to draw in wire-frame).  You can display some objects solid
and some in wire-frame.

And finally, if you really want beautiful pictures with perfect
transparency, RenderMan (a commerical product from Pixar, Inc.)  is
the way to go.  You can use Geomview to set up the scene the way you
want it and to create a RIB file, then use RenderMan to render that
file into an image.  It's slow --- sometimes taking several minutes to
generate a single picture, but the results look great.  All this
depends, of course, on your having RenderMan, which is rather
expensive.  If you happen to have it already and would like more
information about using it with Geomview, just let me know.

Hope this helps,

Mark Phillips
Geometry Center