[vtkusers] How to use backface culling with polylines
Sebastien Jourdain
sebastien.jourdain at kitware.com
Sat Nov 20 10:00:26 EST 2010
Hi Donny,
you can also build the normal vector of the clipping plane by the
earth center and the camera position ?
Seb
On Sat, Nov 20, 2010 at 9:07 AM, Donny <donnyz at charter.net> wrote:
> Hello again. I decided to try David's approach with clipping planes. Mainly
> because I will have quite a few lines when including the county lines in
> addition to the state lines and I did not want to create that many
> triangles. I was afraid it would slow down the performance.
>
> I have centered the clipping plane at the center of the earth and the normal
> is always the view normal. This works great when the focus point is on the
> surface of the earth and I rotate around it. The problem occurs when I pan.
> This moves the camera focal point and when it is no longer on the surface of
> the earth the clipping plane will show some details on the other side of the
> horizon. How can I force a pan operation to pan the focal point on the
> surface of the earth?
>
> Here is the pan code, I am using .NET delegates because of the static
> function pointer limitation for AddObserver:
>
> void OnVtkMiddleMouseDown(unsigned long eventId, System::Object^ clientData)
> {
> this->m_interactorstyle->StartPan();
> }
>
> void OnVtkMiddleMouseUp(unsigned long eventId, System::Object^ clientData)
> {
> this->m_interactorstyle->EndPan();
> }
>
> void OnVtkMouseMove(unsigned long eventId, System::Object^ clientData)
> {
> switch (this->m_interactorstyle->GetState())
> {
> case 1: //VTKIS_ROTATE
> this->Rotate();
> break;
>
> case 2: //VTKIS_PAN
> this->Pan();
> break;
>
> case 4: //VTKIS_DOLLY
> this->Dolly();
> break;
> }
> }
>
> void Pan()
> {
> // Get the vector of motion
>
> double focalPoint[3];
> double v[3];
> double p1[4];
> double p2[4];
>
>
> double* pos = m_camera->GetPosition();
> double* fp = m_camera->GetFocalPoint();
>
>
> vtkInteractorStyleUser::ComputeWorldToDisplay(m_backgroundrenderer,
> fp[0], fp[1], fp[2], focalPoint);
>
>
> vtkInteractorStyleUser::ComputeDisplayToWorld(m_backgroundrenderer,
> m_iren->GetEventPosition()[0], m_iren->GetEventPosition()[1],
> focalPoint[2], p1);
>
>
> vtkInteractorStyleUser::ComputeDisplayToWorld(m_backgroundrenderer,
> m_iren->GetLastEventPosition()[0], m_iren->GetLastEventPosition()[1],
> focalPoint[2], p2);
>
> double npos[3];
> double nfp[3];
>
> for (int i = 0; i < 3; i++)
> {
> v[i] = p2[i] - p1[i];
> npos[i] = pos[i] + v[i];
> nfp[i] = fp[i] + v[i];
> }
>
> m_camera->SetPosition(npos);
> m_camera->SetFocalPoint(nfp);
>
> this->m_iren->Render();
>
> }
>
> Thanks.
>
> -----Original Message-----
> From: David Gobbi [mailto:david.gobbi at gmail.com]
> Sent: Thursday, November 18, 2010 9:07 PM
> To: Donny
> Cc: vtkusers at vtk.org
> Subject: Re: [vtkusers] How to use backface culling with polylines
>
> You could also add a clipping plane to your vtk mapper that cuts the
> globe in half, back to front. By adding this plane only to the mapper
> that renders the lines, you can remove any lines that are past the
> horizon.
>
> David
>
>
> On Thu, Nov 18, 2010 at 7:13 PM, Jim Peterson <jimcp at cox.net> wrote:
>> 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
>>> _______________________________________________
>>> Powered by www.kitware.com <http://www.kitware.com>
>>>
>>> Visit other Kitware open-source projects at
>>> http://www.kitware.com/opensource/opensource.html
>>>
>>> Please keep messages on-topic and check the VTK FAQ at:
>>> http://www.vtk.org/Wiki/VTK_FAQ
>>>
>>> Follow this link to subscribe/unsubscribe:
>>> http://www.vtk.org/mailman/listinfo/vtkusers
>>>
>>>
>>>
>>>
>>> --
>>> | Aashish Chaudhary
>>> | R&D Engineer
>>> | Kitware Inc.
>>> | www.kitware.com <http://www.kitware.com>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> Powered by www.kitware.com
>>>
>>> Visit other Kitware open-source projects at
>>> http://www.kitware.com/opensource/opensource.html
>>>
>>> Please keep messages on-topic and check the VTK FAQ at:
>>> http://www.vtk.org/Wiki/VTK_FAQ
>>>
>>> Follow this link to subscribe/unsubscribe:
>>> http://www.vtk.org/mailman/listinfo/vtkusers
>>>
>>
>>
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at: http://www.vtk.org/Wiki/VTK_FAQ
>
> Follow this link to subscribe/unsubscribe:
> http://www.vtk.org/mailman/listinfo/vtkusers
>
More information about the vtkusers
mailing list