[vtkusers] depth sorting problems?

[Steven Chall]

Thanks, Bill.

-Steve

From: Bill Lorensen [mailto:bill.lorensen at gmail.com]
Sent: Thursday, May 12, 2011 10:20 AM
To: Steven Chall
Cc: vtkusers at vtk.org
Subject: Re: [vtkusers] depth sorting problems?

This page may help:
http://vtk.org/Wiki/VTK/Examples/Cxx/Visualization/CorrectlyRenderingTranslucentGeometry

On Tue, May 10, 2011 at 12:32 PM, Steven Chall <stevec at renci.org<mailto:stevec at renci.org>> wrote:
Please look at the attached images, showing two sets of structures (vtkPolyData objects) constructed inside a loop using the code included below.  I strongly believe that the code for the two images is identical except that actor->GetProperty()->SetOpacity(...) is being called for c113_transparent.png with an argument < 1.0.

c113_opaque.png  (opacity == 1.0) looks ok.  But c113_transparent.png (opacity < 1.0) has various kinds of ugly rendering artifacts that show up when opacity isn't all the way on, maybe sorting errors?   Also, note that the ordering of the structures is wrong front-to-back when opacity is less than full:  for example, the brown structure appears to be in front of the red and dark gray ones, but it's not when opacity is full on (nor should it be).  I'm trying various combinations of normal parameter values, e.g., flipped, not flipped, etc., but I haven't found the right combination to make partial transparency acceptable.

I'm running VTK 5.6.1 with Qt 4.7.1 in Win7 Enterprise, all 32 bits, on a ThinkPad with a 1.6 GHz i7 (Q720) cpu and 4 GB RAM. Thanks for any suggestions.

-Steve

vtkPoints *points = vtkPoints::New();

    //...read in a bunch of vertices...

  vtkCellArray *polys = vtkCellArray::New();

    // ...likewise read in a bunch of edges to connect the vertices...

  if (structure) structure->Delete();
  structure = vtkPolyData::New();
  structure->SetPoints(points);
  points->Delete();
  structure->SetPolys(polys);
  polys->Delete();

  if (deci) deci->Delete();
  deci = vtkDecimatePro::New();
  deci->SetInput(structure);
  deci->SetTargetReduction(0.5);
  deci->PreserveTopologyOn();

  if (smoother) smoother->Delete();
  smoother = vtkSmoothPolyDataFilter::New();
  smoother->SetInputConnection(deci->GetOutputPort());
  smoother->SetNumberOfIterations(100);

  if (normals) normals->Delete();
  normals = vtkPolyDataNormals::New();
  normals->SetInputConnection(smoother->GetOutputPort());
  normals->FlipNormalsOn();
 normals->AutoOrientNormalsOn();
  normals->NonManifoldTraversalOff();
  normals->ConsistencyOn();
  //normals->ComputeCellNormalsOn();

  if (mapper) mapper->Delete();
  mapper = vtkPolyDataMapper::New();
  mapper->SetInputConnection(normals->GetOutputPort());

  if (actor) actor->Delete();
  actor = vtkActor::New();
  actor->SetMapper(mapper);
  actor->GetProperty()->SetInterpolationToPhong();

  if (transparency != 0.0)
  {
    //normals->FlipNormalsOff();
    actor->GetProperty()->SetOpacity(1.0 - (transparency / 100.0));
  }

  actor->GetProperty()->SetSpecular(4);
  actor->GetProperty()->SetSpecularPower(30);
  actor->GetProperty()->SetColor(clr[0], clr[1], clr[2]);
  actor->GetProperty()->SetSpecularColor(1, 1, 1);

  renderer->AddActor(actor);



-Steve Chall
 Senior Research Software Developer
 Renaissance Computing Institute (RENCI)
 Phone: 919-681-9639<tel:919-681-9639>
 Email: stevec at renci.org<mailto:stevec at renci.org>


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