[vtkusers] RE Request to VTK Multi-Pass Rendering

Thu Nov 26 07:03:33 EST 2009

Hi Stephane,

Thank you for your replay with an overview of the advanced rendering opportunities in VTK ! I will look at the ParaView-Example for the hidden lines removal. But the multipass-framework is still of interest for me because I want to use more sophisticated multipass-rendering techniques later. Ok, but for now I take a look insight painters. :-)

Best regards,

Rocco

From: Stephane PLOIX [mailto:stephane.ploix at edf.fr] 
Sent: Tuesday, November 24, 2009 11:58 AM
To: post at rocco-gasteiger.de
Cc: vtkusers at vtk.org
Subject: RE [vtkusers] Request to VTK Multi-Pass Rendering

Hi Rocco, 

Here is a general picture of the different ways you can implement advanced rendering effects in VTK : 
*shaders : each vtkProp can have a shader, this is mostly used in single pass algorithms 
*painters : you can implement a per-prop multipass algorithm in a painter, as is done in the plugin example in ParaView/Example/Plugins/HiddenLinesRemoval which does exactly what you need. 
*renderpass : this framework is intended for algorithm that need global information of all props : you can implement post-processing algorithms like screen-space ambient occlusion or edge-detection filters, and algorithms that require several passes of all the props, like shadow mapping. 

Best, 
Stephane

post at rocco-gasteiger.de 
Envoyé par : vtkusers-bounces at vtk.org 

23/11/2009 10:51 

A

vtkusers at vtk.org 

cc

Objet

[vtkusers] Request to VTK Multi-Pass Rendering

Dear VTK users, 

I want to use the new mulit-pass framework in VTK implemented by François Bertel. At first, many thanks François for implementing this framework! I need some multipass rendering for my research project and I think you have provided a very good base for start-up with this. 

For a better understanding how it works, I tried to adopt a native multi-pass OpenGL example in VTK, with help of the given framework. In doing so I oriented me at the given examples on the according VTK Wiki sites. Unfortunately, I did not get the same result in VTK like in OpenGL. I think I miss some important facts of understanding the VTK rendering pipeline. So I hope somebody (maybe François directly) can help me to have a better understanding of how the framework works.  Here comes what I really do: 

In OpenGL I implemented an algorithm for hidden line removing (It is based on the paper of Jarek R. Rossignac and Maarten van Emerik: Hidden contours on a frame-buffer (1992) ). Here is a snippet of my OpenGL code, where I have to render my geometry two times (2-passes). 

glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
glEnable(GL_DEPTH_TEST); 
glColor3f(0,0,0); 

// Settings for first pass 
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE,GL_FALSE); 
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL); 
drawMyGeometryWithSolidFaces(); 

// Settings for second pass 
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE,GL_TRUE); 
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); 
glEnable(GL_POLYGON_OFFSET_LINE); 
glPolygonOffset(-1.0,1.0); 
drawMyGeometryWithSolidFaces(); 

// Reset polygon offsest 
glDisable(GL_POLYGON_OFFSET_FILL); 

In VTK I derived a class “vtkHiddenLineDesignerPass” from “vtkRenderPass” and tried to implement the same OpenGL steps. The result is, that still all lines are rendered, also the hidden lines. I use the following lines of code snippets in the “Render(const vtkRenderState *s)”-function to adopt the OpenGL-code with VTK datastructures and calls: 

//** Getting necessary VTK-objects to turn on/off some OpenGL-states.**/ 
vtkOpenGLRenderer *r=static_cast<vtkOpenGLRenderer *>(s->GetRenderer()); 
vtkActor *actor = r->GetActors()->GetLastActor(); 
vtkPolyDataMapper *actorMapper = static_cast<vtkPolyDataMapper*>(actor->GetMapper()); 
vtkProperty *actorProp = actor->GetProperty(); 

// Settings for the first pass // 
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE,GL_FALSE); 
actorProp->SetRepresentationToSurface(); //** For glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);**// 
this->DelegatePass->Render(s); 
this->NumberOfRenderedProps += this->DelegatePass->GetNumberOfRenderedProps(); 

// Settings for the second pass // 
actorProp->SetDiffuseColor(0,0,0); //** For glColor3f(0,0,0); **// 
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE,GL_TRUE); 
actorProp->SetRepresentationToWireframe();  //** For glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); **// 
actorMapper->SetResolveCoincidentTopology(1); 
actorMapper->SetResolveCoincidentTopologyToPolygonOffset(); 
actorMapper->SetResolveCoincidentTopologyPolygonOffsetFaces(0); //** For glEnable(GL_POLYGON_OFFSET_LINE);**// 
actorMapper->SetResolveCoincidentTopologyPolygonOffsetParameters(-1.0,1); //** For glPolygonOffset(-1.0,1.0);**// 

this->DelegatePass->Render(s); 
this->NumberOfRenderedProps += this->DelegatePass->GetNumberOfRenderedProps(); 
actorMapper->SetResolveCoincidentTopology(0); //** For glDisable(GL_POLYGON_OFFSET_FILL);**// 

In my VTK-class, where I use this rendering pass, I process following rendering pipeline: 
// The elementary passes. 
vtkLightsPass *lights=vtkLightsPass::New(); 
vtkDefaultPass *defaultPass=vtkDefaultPass::New(); 

// Put them in a sequence. 
vtkRenderPassCollection *passes=vtkRenderPassCollection::New(); 
passes->AddItem(lights); 
passes->AddItem(defaultPass); 

vtkSequencePass *seq=vtkSequencePass::New(); 
seq->SetPasses(passes); 

// Make the sequence the delegate of a camera pass. 
vtkCameraPass *cameraP=vtkCameraPass::New(); 
cameraP->SetDelegatePass(seq); 

// Create the hidden line removing pass and attach the camera pass as its delegate 
vtkHiddenLineDesignerPass *myPass=vtkHiddenLineDesignerPass::New(); 
myPass ->SetDelegatePass(cameraP); 

vtkRenderer* renderer01= vtkRenderer::New(); 
renderer01->SetPass(myPass); 

Especially, my misunderstanding relies on when to use native OpenGL-code and when using VTK-calls. I tried some variations of  the code, presented above but without success. It would be very helpful if someone can give me some hints. 

Many thanks in advance, 
Rocco Gasteiger 

-------------------------------------------------- 
Dipl.-Ing. Rocco Gasteiger 
Otto-von-Guericke University
Faculty of Computer Science
Department of Simulation and Graphics
Universitätsplatz 2, 39106 Magdeburg, Germany 

Office:  G29-223 
Phone:   +49 391 67 127 59
Fax:     +49 391 67 111 64 
Website: http://wwwisg.cs.uni-magdeburg.de/cvcms/  
-------------------------------------------------- 

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