[vtkusers] Re: Edge (region?) Visibility

[Goodwin Lawlor]

Hi,

I put up an alternative (better) script that uses the dot product of the 
   triangle normal and the vector from the camera position to a point on 
the polygon... means you can use perspective view instead of parallel.

Have a look here:

http://www.bioengineering-research.com/vtk/BackfaceCull2.tcl

Goodwin

Goodwin Lawlor wrote:
> Hi Juan,
> 
> You can have a look at a tcl example that backface culls polygons before 
> rendering... this allows you to count visible polygons or edges. Its here:
> 
> http://www.bioengineering-research.com/vtk/BackfaceCull.tcl
> 
> If you need better performance, the cvs version of VTK backface culls 
> wireframes... if you render into the openGL feedback buffer you can 
> count the visible edges there (Look at how vtkGL2PSExporter does it). 
> This could be more hassle than its worth though.
> 
> If you'd like a stand alone exe to run the tcl file, try this:
> 
> http://www.bioengineering-research.com/vtk/vtkit.htm
> 
> hth
> 
> Goodwin
> 
> Juan Ignacio Sánchez Lara wrote:
> 
>> Hello all,
>>
>> I've been told to use VTK library and I must admit I'm quite lost, so 
>> I'd like to ask you for help.
>>
>> I must implement an application which receives polygons and a "camera 
>> point" as input (everithing in 2D), and it must return the segments of 
>> the polygon edges which are visible from that point. What do you 
>> reccomend me to use? The only documentation I've found is the library 
>> API, and it's quite hard to begin that way...
>>
>> Every kind of help would be greatly appreciated!
>>
>> best regards,
>>
>> -- 
>> Juan Ignacio Sánchez Lara
>> Ingeniero Técnico en Informática de Sistemas
>>
>>
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