Thanks much for the feedback. There are indeed a variety of bugs in the
new VPython, plus one necessary "feature". The "feature" is this: the
new transparency capability is an example of "go fast, be wrong". It's
wonderful to have transparency, but it is not difficult to create a
scene where transparency doesn't work properly. Non-opaque objects are
ordered back to front for rendering purposes, so that those in front can
have some of the color of those in back. The ordering is based on the
center of the object. So for example a long transparent cylinder whose
center is at (0,0,0) but whose axis runs along (1,0,1) is treated as
though all parts of its axis were at z=0, which is incorrect. Something
like this is what's happening with your cone example.
I'd like to take the opportunity on behalf of the VPython community to
thank Jonathan Brandmeyer for his huge contributions to the development
of VPython. He carried off two major developments. The first was to
create an auto-configure installation mechanism which addressed severe
problems that had existed with compiling and installing Visual on
Linux/Unix platforms. The second was the new capabilities of
transparency, surface textures, and sophisticated lighting. These
represent an enormous step up for VPython. It also represents a
fundamental change in the architecture of the Visual module, and because
of that it will take some time to identify and fix the bugs. What he has
done is not a simple addition to Visual but a major rewrite.
Jonathan just graduated from NCSU in engineering. He encountered VPython
during two semesters of introductory physics (Matter & Interactions)
taught by Ruth Chabay and me. He got interested in the underlying
software and began working on development. Alas, he is about to get a
job in the real world and won't be free to spend large amounts of time
on VPython. With his help, I'm trying to come up to speed on the new
VPython as quickly as possible so that I can maintain and document it,
but there's an awful lot to learn, having been mostly away from working
with the software for the last several years while Chabay and I were
focussed on getting our physics curriculum to work at NCSU. I'm at the
point now where I can compile and fix simple bugs on Linux (in CVS are
some simple bug fixes for textures) but for some reason haven't yet
succeeded in compiling on Windows, which is a high priority.
Again, thanks, Jonathan!
Bruce Sherwood
Rob Salgado wrote:
>Thanks for 4.0beta2. It looks like it has some nice new features. I look
>forward to learning how to use them!
>
>
>I thought I'd mention some of the issues I have had with the latest beta.
>I apologize that I have not had the time to isolate the key issues myself.
>Maybe someone can spot the problems. (I should mention that I am going
>from Python2.3.4-VPython2003-10-05b to Python2.4.4-VPython4.0beta2. It
>maybe that some of my issues already appear in VPython3.2.9.exe .)
>
>First, it seems that the VPython windows don't react to keys anymore.
>ESC doesn't seem to terminate the window. Keystrokes don't seem to be
>caught with scene.kb.keys / scene.kb.getkey().
>
>
>Second, here is a transparency example which seems to show a weird artifact.
>
>from visual import *
>scene.background=color.blue
>
>for r in arange(.1,1.1,.1):
> sphere(pos=(0,0,0), radius=r, alpha=1.1-r)
>
>C1=cone(pos=(0,0,0),axis=vector(0.5,1,0),alpha=.25,color=color.yellow,radius=1.25)
>
>while 1:
> rate(20)
> C1.rotate(angle=0.2,axis=vector(1,1,1))
>
>
>Third, here is a more involved program which animates Ampere's Law.
>http://www.physics.syr.edu/~salgado/software/vpython/Maxwell-Ampere.py
>The keys (a) (e) (i) (d) (n), which toggle features in the display, don't
>work in the new beta [as mentioned above]. In addition, the green and blue
>figures are supposed to be [size-modified] arrows... but they show up as
>squares in the new beta.
>
>
>By the way, I am able to run these programs in both Python23 and Python24
>by use of a registry hack, which is available on
>http://www.physics.syr.edu/~salgado/software/vpython/
>
>Any assistance on the issues raised would be appreciated.
>
>Thanks.
>
>rob salgado
>
>
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