RE: [Visualpython-users] Re: VPython questions (fwd)

[David S. <dsc...@cm...>]

> Currently the smoothness of a Visual sphere is determined by a heuristic
> based on how far away the sphere is. We think that the current
> setting errs
> a bit too far on the side of speed at the expense of visual quality. There
> is currently no option for controlling this.

Not without rebuilding cvisual, no.  I agree that an option would be nice.
There is also a problem with the way the level-of-detail heuristic works; it
doesn't take into account the size of the window or of the screen, so
spheres in a large window will look much worse than spheres in a small
window.

I am *extremely* busy at the moment, but someone else is welcome to hack up
sphere.cpp.  Just search for

// Level of detail heuristic
//   xxx Figure out how this should actually work!

and follow those instructions :)

> > 2. Is transparency possible?.
> > I though openGL did it, but I don't see a way to control this.
> > Transparency would be very helpful for all sorts of special
> visualization
> > and intersections etc..

OpenGL implements alpha rendering, but transparency places severe
restrictions on the rendering pipeline.  In particular objects need to be
drawn in back-to-front order, which is not necessary for opaque objects
thanks to Z buffering.  Implementing transparency in an environment as
unrestrictive as Visual without exposing the additional complexity to the
user is not (quite) trivial.

> I did not uninstall my existing Python for fear I would loose some work,
> time and  functionality. I did not want to disturb my present happy
> working conditions [if it aint broke dont fix it].. So I installed
> VPython in its own folder on another drive to test it out first. Then I
> started copying the cvisual.dll into other python installations I have to
> seee if I could get it to work.

From the FAQ:

Q: Why do I have to uninstall Python before installing VPython?

A: The VPython installer for Windows is a superset of Python 1.5.2, but the
installation program is not sophisticated enough to perform an upgrade "in
place" and ensure that subsequent uninstallation will work properly. You can
try to do an upgrade yourself by installing the Visual library
(http://cil.andrew.cmu.edu/projects/visual/download/Visual-2000-10-05.zip)
and upgrading IDLE (http://sourceforge.net/projects/idlefork), but for most
people it will be easier to uninstall 1.5.2 and run our installer. VPython
can coexist with versions of Python later than 1.5.2.

> > I launched it successfully from IDLE but when I closed any
> VPython window
> > it would crash the Python version. What is going on here? I know you say
> > it would break.. but WHY?

The problem is that the IDLE that comes with normal versions of Python, and
most other development environments for Python, run user programs in its own
process.  For example, if you write a loop like this (with or without
visual)

while 1:
  pass

you will crash IDLE.  Most of the VPython demo programs do almost exactly
that!  If you use the following approach instead:

scene.exit=0
scene.visible=1
while scene.visible:
    pass

you may be able to get things to work.  However, I recommend using the IDLE
fork that comes with VPython (see the above link for a separate download).

Dave