[IGSTK-Users] vtkPolyData transparency trouble

[Patrick Cheng]

Hi Romain Carpentier,

Transparency has always been a problem. IGSTK currently doesn't have a 
effective way to deal with it.

Thank you for sharing your solution. It will be nice if IGSTK could do 
something similar. But it's a little tricky to implement your solution 
in IGSTK, because it needs access to both mesh data and the camera, 
which are encapsulated separately in representation and view class.

Do you have any design in mind for fixing it?

Thank you,

Patrick



Romain Carpentier wrote:
> Hi everybody,
> 
> I'm currently working on an image-guided neurosurgery application based
> on IGSTK. In this application, the visualization widget exposes 3
> orthogonal views and a 3D view in which we display several vtkPolyData,
> each owning its color and opacity (around 0.5).
> 
> The problem is that deciding whether one part of a given vtkPolyData is
> behind or in front of a part of another vtkPolyData is sometimes
> impossible. This trouble genuinely can be annoying.
> 
> This problem is due to the way VTK manages transparency along the camera
> view vector through entities' polygons.
> 
> I solved the problem in another application (that does not use IGSTK)
> by :
> 1-initially using a vtkDecimatePro to cull many "useless" polygons
> generated by our tools for the patient's head or brain
> 2-applying a vtkDepthSortPolyData to the output at each frame : this
> uses the camera view vector to sort polygons which are then displayed
> without any ambiguity. The first step (decimation) had to be set and
> leads us to a trade-off between surfaces' quality and framerate. 
> 
> My question is : does IGSTK already offer any solution to this problem?
> If not, how could I solve it using IGSTK?
> 
> Perhaps, a modification in igstkMeshObjectRepresentation and igstkView
> following the solution above could solve it...
> 
> Thank you very much for this great toolkit,
> 
> Romain Carpentier
> Unité/Projet VisAGeS U746
> INSERM/INRIA/CNRS/U. de Rennes I
> IRISA
> Campus de Beaulieu, 35042 Rennes Cedex, France
> 
> email: romain.carpentier at irisa.fr
> http://www.irisa.fr/visages/
> 
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