[vtkusers] Changing the direction of Z

[Paul Harris]

On 27 October 2010 01:43, <jimcp at cox.net> wrote:

> Paul,
>
> I have no doubt we have a shared knowledge gap, and most of it is probably
> on my side. and to be sure I do not have a comprehensive understanding of
> vtk.
>
> When we started on this, you had a problem with "missing or dark triangles
> in some models", and a problem with inverting models that resulted in dark
> polygon displays. You provided an illustrative example with two generated
> cones. One of which displays black triangles when any one axis is reversed
> using an actor defined transform. this was assumed to be a simulation of the
> right handed vs left handed model problem and was addressed by applying the
> transform to the polydata instead of the actor. That was to address the
> problem I thought we were addressing was where "some of my models are right
> handed and some are left handed". in that case, My opinion is you need to
> deal with that difference by individual model at the polydata level. Unless
> you disagree, I think we have arrived at a resonably conclusion in this
> issue.
>
>
Sorry, that wasn't the problem I was trying to address.  All of my models
share the same handedness, but the user may want to mirror the view.


> Now focus has moved to the yet to be demonstrated problem of "Some of my
> models normals are inverted". I am not an expert in this area, but I think
> that class of problem would be addressed in vtk by reducing the contour to
> it's component points, and then generate a new polygon mesh with newly
> computed normals. If you have a readable file you would like to post as an
> example of this issue, I don't mind having a look.
>

I now do not think that is a problem.  All of my models have normals
pointing all over the place, and the models should not need to be fixed, as
I want to see both sides of each polygon anyway (eg planes).


> finally we have a problem "I need to display a mirrored world view". I am
> imagining a display mounted in a kiosk with a mirror reflecting the image. I
> will have to defer to other readers, I agree this might be a camera or
> renderer function. I hope they are still reading....
>
>
Ideally you just add a UserMatrix transform on the camera, thereby reversing
the entire scene.

The problem that you have not listed here is the one I'm trying to highlight
- twosided lighting equations in the presence of UserMatrix transformations.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20101027/bb595046/attachment.htm>