[vtkusers] How to use backface culling with polylines

[Jim Peterson]

Donny,
I think I would run the state lines through a ribbon filter making them 
into a triangle strip of some width. the strip would have a backface.

Jim

Donny wrote:
>
> Thanks guys for the feedback. I have attached two images to visualize 
> what follows. I hope I can explain this clearly.
>
> I have three renderers that I am adding to the render window.
>
> The first is to contain a textured vtkGlobeSource actor and is called 
> the background renderer.
>
> The second contains several vtkPolyData actors and are lines (State 
> and county boundaries, roads, rivers…), this is called the map renderer.
>
> The Third contains an actor visualizing a weather radar volume, this 
> is called the radar renderer.
>
> The background renderer is always set as layer 0 and so is always 
> rendered first.
>
> The map renderer and radar renderer will alternate between the 1^st 
> and 2^nd layers depending on the view angle of the camera.
>
> If the camera is more than 45 degrees above the horizon then the radar 
> renderer is layer 1 and the map renderer is layer 2 so that the user 
> can see the features below the radar volume.
>
> If the camera is less than or equal to 45 degrees above the horizon 
> then the map renderer is layer 1 and the radar renderer is layer 2 so 
> that the radar volume is always in front of the map features.
>
> This works fine until I draw all state lines for the entire US. 
> Because the vtkGlobeSource simulates the curvature of the earth I see 
> the backside of the state lines where they are over the view horizon.
>
> Is there a way I can put the map features and radar volume on the same 
> renderer and accomplish the same thing?
>
> Thanks.
>
> -----Original Message-----
> *From:* Aashish Chaudhary [mailto:aashish.chaudhary at kitware.com]
> *Sent:* Thursday, November 18, 2010 8:37 AM
> *To:* David Gobbi
> *Cc:* vtkusers at vtk.org; Donny
> *Subject:* Re: [vtkusers] How to use backface culling with polylines
>
> Donny,
>
> Were you talking about hidden lines removal may be?
>
> Thanks,
>
> On Thu, Nov 18, 2010 at 9:03 AM, David Gobbi <david.gobbi at gmail.com 
> <mailto:david.gobbi at gmail.com>> wrote:
>
> Jerome is correct, OpenGL culls faces according to the polygon
> winding. So wireframe polygons can be culled, but polylines cannot,
> even if they have normals assigned to them. There are some details in
> the OpenGL FAQ:
> http://www.opengl.org/resources/faq/technical/clipping.htm
>
> David
>
>
> On Wed, Nov 17, 2010 at 11:47 PM, Jérôme <jerome.velut at gmail.com 
> <mailto:jerome.velut at gmail.com>> wrote:
> > Hi Donny,
> >
> > My feeling is that backface culling should not work with polylines 
> because they
> > have actually no face.
> >
> > Jerome
> >
> > 2010/11/18 Donny <donnyz at charter.net <mailto:donnyz at charter.net>>:
> >> I am drawing polylines using vtkPolyData and cannot get backface 
> culling to
> >> work with them.
> >>
> >>
> >>
> >> I ran into this subject
> >> 
> http://public.kitware.com/pipermail/vtkusers/2003-January/065023.html 
> , but
> >> did not help.
> >>
> >>
> >>
> >> Any solutions?
> >>
> >>
> >>
> >> Donny Zimmerman
> >>
> >> donnyz at charter.net <mailto:donnyz at charter.net>
> >>
> >> 308-227-1756
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>
> -- 
> | Aashish Chaudhary
> | R&D Engineer
> | Kitware Inc.
> | www.kitware.com <http://www.kitware.com>
>
> ------------------------------------------------------------------------
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