[Closed REQ 5263]:

["Tamara Munzner" <munzner>]

>1. I tried to use "Commands" on PANELS menu.  I tried "clock" for
>testing.  However, I have the following message:
>	"clock: No such file or directory".
>I don't know what is wrong with my Geomview.  Is this means
>that my installation is wrong or I used wrong command format?

You're just using the wrong format. Geomview commands (also known as
GCL, for Geomview Command Language) are always wrapped in parentheses.
Also, the clock command returns a value, which will only get printed
out if the output of the "clock" command is passed to the "echo"
command. So you want to say this:

 (echo (clock))

>2. Is there any data format for a set of 2-dimensional polygons? 
 
No, there is no specific format for 2D polygons.  Just use 3D polygons
which all have the same value for one of the coordinates (setting the
Z coordinate to 0 would be the most convenient, given the default
setting of the camera).

>3. How to shade two sides (front and rear) of one object with
>different colors and with only one (front or rear) normal vector? 

Use the "backdiffuse" material setting to make the rear a different
color than the front, and turn off the "evert" appearance setting to
disable flipping the normal vector when it doesn't face the camera.
For example, the following command disables normal-flipping (which is
what you're asking for) and colors the front green, the rear blue:

(merge-baseap 
 { appearance -evert material {diffuse 0 1 0 backdiffuse 0 0 1 }})

If you put this kind of a command in a file called ".geomview" in your
home directory, all surfaces will be drawn this way automatically. On
the Sun version of Geomview, this should always work. On the SGI
version of Geomview, you might need to turn on software shading (with
the key sequence "1v~") if twosided surfaces are not supported in
hardware on your particular machine.

Hope this helps,

Tamara Munzner		The Geometry Center	     ((555) 555-5555
munzner at geom.umn.edu    http://www.geom.umn.edu/people/munzner.html