[vtkusers] Polydata + translucent volume

Lisa Avila lisa.avila at kitware.com
Mon Jul 28 13:59:37 EDT 2003

Hello Janne,

Does your cursor have an opacity less than 1.0? If so, it will not work 

vtkDepthSortPolyData is a class to use when you need to sort the polygons 
(within one vtkPolyData) for correct (back-to-front) ordering for 
translucent rendering. You should not need this class for this problem.

The order in which you add the props should not matter.


At 08:11 AM 7/25/2003, Hämäläinen Janne wrote:
>Hi all,
>I'm rendering 3D volume using predefined vtkColorTransferFunction and scalar
>opacity function, and trying to render a 3D cursor (vtkCursor3D) into the
>same scene. Problem is that although the focal point of the cursor should be
>inside the visible part of the volume, it is rendered so that it is appears
>to be outside the volume, i.e., so that there is no translucent volume
>hiding it ( the cursor is the closest object to camera from view points ).
>I've understood that there could be sometimes problems in ordering polydata
>if there is objects in scene that has opacity less than 1. I've tried to
>order actors in the renderer as was suggested in the vtk handbook ( volume
>first and cursor last )  and also tried vtkDepthSortPolyData ( although
>didn't understand how it works ), but nothing has helped. If someone has
>knowledge on what I should do, please let me know.
>Cheers, Janne
>Janne Hämäläinen
>Research Assistant
>Helsinki University Central Hospital
>X-ray Department
>email   janne.hamalainen at hus.fi
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