Re: [Visualpython-users] Transparency question

On Wed, Mar 21, 2001 at 02:03:28PM -0600, Art...@rs... wrote:
> > Actually on the plate for the second half of this semester is a bunch of new
> > stuff in VPython. Transparency will be tricky to do due to structural issues
> > in VPython (transparency in GL requires careful observance of zbuffer and
> > render-order rules) but textures should be starting to happen in the next
> > couple of weeks.
> 
> What am I missing here on the transparency issue?   I am thinking
> basic Color4  with the alpha value component set to 1 by default
> but with the ability to override the default and toggle on the appropriate
> glEnables.  Do I not understand something basic about how VPython does
> OpenGL or are you referring to a more sophisticated transparency
> implementation?
> 
Dave Andersen was talking with Dave Scherer about this on
visualpython-devel.

The problem is, to get alpha right, you have to make sure you render the
scene back-to-front, or the color values in the output buffer won't be
correct when you use them to do alpha computations at each stage in the
rendering.

Unfortunately, the current VPython implementation's scene conception doesn't
support this strong ordering on the objects in the scene ...


Ari