Draw an actor always on top of the secene.

Support
1

Little context
I pick faces of polydata with a custom interactor style and want to display as a highlighted. To do this I create a temporary actor with different color, larger line width, reduce opacity on other actors etc. But the pick is not always clear. Currently I try these properties,

                pPickedActor->GetProperty()->SetDiffuseColor(1.0, 1.0, 0.0);
                pPickedActor->GetProperty()->SetDiffuse(1.0);
                pPickedActor->GetProperty()->SetSpecular(0.0);
                pPickedActor->GetProperty()->SetLineWidth(3.0);

Is it possible to draw this actor last or on top of all the other actors so that the picking is clearly visible?
Note : I cannot change the property of the entire actor as the cells of faces are subset of the actor.

Thanks!

2

On the mappers, you can set these properties to make one appear on top of another.

ActiveMapper->SetRelativeCoincidentTopologyLineOffsetParameters(0, -66000);
ActiveMapper->SetRelativeCoincidentTopologyPolygonOffsetParameters(0, -66000);
ActiveMapper->SetRelativeCoincidentTopologyPointOffsetParameter(-66000);
LinesMapper->SetRelativeCoincidentTopologyLineOffsetParameters(-1, -1);
LinesMapper->SetRelativeCoincidentTopologyPolygonOffsetParameters(-1, -1);
LinesMapper->SetRelativeCoincidentTopologyPointOffsetParameter(-1);
3

Hello,

Alternativelly, you can try using two renderers and set one of them to be the topmost:

   m_rendererMainScene->SetLayer( 0 ); //the renderer of layer 0 has background and is rendered first.
   m_rendererForeground->SetLayer( 1 ); //layers greater than zero have no background and are rendered afterwards.

regards,

PC

1 Like
4

@Paulo_Carvalho Interesting suggestion. Could this be used to draw an opaque actor after a transparent one (breaking the usual order of rendering)?

5

Thanks for this! @Paulo_Carvalho

Code snippet for future users

vtkSmartPointer<vtkRenderer> pDefaultRenderer = vtkSmartPointer<vtkRenderer>::New();
pDefaultRenderer ->SetBackground(0.1, 0.2, 0.3);
pDefaultRenderer ->SetLayer(0);

// Add actors to be rendered on top in pvtkForgroundRenderer 
vtkSmartPointer<vtkRenderer> pvtkForgroundRenderer = vtkSmartPointer<vtkRenderer>::New();
pvtkForgroundRenderer->SetActiveCamera(pDefaultRenderer ->GetActiveCamera()); // Set same camera as default render
pvtkForgroundRenderer->SetLayer(1);

vtkSmartPointer<vtkRenderWindow>  pVtkRenderWindow = vtkSmartPointer<vtkRenderWindow>::New();
pVtkRenderWindow->SetNumberOfLayers(2);

pVtkRenderWindow->AddRenderer(pDefaultRenderer);
pVtkRenderWindow->AddRenderer(pvtkForgroundRenderer);
pVtkRenderWindow->Render();
2 Likes
6

Yes, it can:

image
image463×632 56.2 KB

In the example above, the label actor is rendered with a foreground renderer. The pilars, containing translucent segments, are rendered in a background renderer. The white text is rendered after all the background renderer’s scene completes rendering, thus it appears unaffected by the alpha blending.

take care,

PC

1 Like