[vtkusers] Tips for the display of a fixed size origin marker

[David Gobbi]

Hi Serge,

In this case, you can just set both the renderers to have the same camera.

 - David

On Mon, Mar 16, 2015 at 7:46 AM, Serge Lalonde <serge at infolytica.com> wrote:

>  Hi Miroslav and David,
>
> Thanks for the suggestions. That's what I was looking for.
> I'll implement it using a separate renderer to avoid mixing actors and to
> set the layer.
> I just need to read up on synchronizing the cameras between the two
> renderers and it should work.
>
> Thanks!
>
>
> On 3/13/2015 5:32 PM, Miroslav Drahos wrote:
>
> Sent my email response a bit too early, sorry.
>
> If you decide to layer the renderers, you'll probably want to set the foreground renderer as non-interactive (vtkRenderer::SetInteractive(0)) otherwise it will be grabbing the events from interactors.
> Cheers,
> Miro
>
>
> ________________________________________
> From: Miroslav Drahos
> Sent: Friday, March 13, 2015 2:28 PM
> To: David Gobbi; Serge Lalonde
> Cc: vtkusers at vtk.org
> Subject: RE: [vtkusers] Tips for the display of a fixed size origin marker
>
> You could stack two renderers, assign the layer number to them (vtkRenderer::SetLayer(int) and vtkRenderWindow::SetNumberOfLayers(int) ) and have the one that's on top contain the origin label actor. That way it will always be visible (as a top layer).
>
> ________________________________________
> From: vtkusers [vtkusers-bounces at vtk.org] On Behalf Of David Gobbi [david.gobbi at gmail.com]
> Sent: Friday, March 13, 2015 2:23 PM
> To: Serge Lalonde
> Cc: vtkusers at vtk.org
> Subject: Re: [vtkusers] Tips for the display of a fixed size origin marker
>
> Hi Serge,
>
> To get the scale right, I add an observer for the renderer's StartEvent
> that does all the necessary calculations to set the position and scale
> of the actor correctly just before the render occurs.  It's kind of messy,
> but I don't know a better way.  The code that I use to compute the
> correct actor scale is as follows:
>
> void ComputeScale(const double position[3], vtkRenderer *renderer)
> {
>   // Find the cursor scale factor such that 1 data unit length
>   // equals 1 screen pixel at the cursor's distance from the camera.
>   // Start by computing the height of the window at the cursor position.
>   double worldHeight = 1.0;
>   vtkCamera *camera = renderer->GetActiveCamera();
>   if (camera->GetParallelProjection())
>     {
>     worldHeight = 2*camera->GetParallelScale();
>     }
>   else
>     {
>     vtkMatrix4x4 *matrix = camera->GetViewTransformMatrix();
>     // Get a 3x3 matrix with the camera orientation
>     double cvz[3];
>     cvz[0] = matrix->GetElement(2, 0);
>     cvz[1] = matrix->GetElement(2, 1);
>     cvz[2] = matrix->GetElement(2, 2);
>
>     double cameraPosition[3];
>     camera->GetPosition(cameraPosition);
>
>     double v[3];
>     v[0] = cameraPosition[0] - position[0];
>     v[1] = cameraPosition[1] - position[1];
>     v[2] = cameraPosition[2] - position[2];
>
>     worldHeight = 2*(vtkMath::Dot(v,cvz)
>                      * tan(0.5*camera->GetViewAngle()/57.296));
>     }
>
>   // Compare world height to window height.
>   int windowHeight = renderer->GetSize()[1];
>   double scale = 1.0;
>   if (windowHeight > 0)
>     {
>     scale = worldHeight/windowHeight;
>     }
>
>   return scale;
> }
>
> For the other question, it sounds like you want VTK to ignore the depth
> buffer when it renders your actor.  I don't know if this is possible.  If I need
> an annotation or a cursor to be in front of everything, I do a pick to find the
> depth (i.e. frontmost object) at the position where I want to render my cursor,
> and then I place my cursor at that depth.
>
>  - David
>
>
> On Fri, Mar 13, 2015 at 2:54 PM, Serge Lalonde <serge at infolytica.com<mailto:serge at infolytica.com> <serge at infolytica.com>> wrote:
> Anyone have any suggestions on how to implement the display of the origin?
> It doesn't have to be axes (although that would be nice).
> The trick is to get it to be a fixed size regardless of the camera zoom and to make it visible even if "hidden" inside of another actor.
>
> Thanks for any tips.
> --www.infolytica.com <http:://www.infolytica.com>
> 300 Leo Pariseau, Suite 2222, Montreal, QC, Canada, H2X 4B3(514) 849-8752 x236<tel:%28514%29%20849-8752%20x236> <%28514%29%20849-8752%20x236>, Fax: (514) 849-4239<tel:%28514%29%20849-4239> <%28514%29%20849-4239>
>
>
>
> --
> www.infolytica.com
> 300 Leo Pariseau, Suite 2222, Montreal, QC, Canada, H2X 4B3
> (514) 849-8752 x236, Fax: (514) 849-4239
>
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