[vtkusers] Weird render bug with depth peeling and background texture

[Benjamin Hopfer]

I have a very weird problem with the render window. It only occurs if:

 - vtkRenderer was set to display a background texture at least once since
program start
 - The background texture has a transformation (scaling for repeat)
 - Depth peeling is enabled
 - At least one transparent actor is displayed.

I'm pretty sure this is a bug, but I wanted to get your insight first,
before reporting it.
I attached a minimal working example below. You can use any png file for
texture.png. I used a 2x2 pixel PNG with (0,0) and (1,1) black and the
other two white (checker board).

I have uploaded the output of the code: http://imgur.com/a/olUW2

 - The first image is the "expected" outcome, which I retrieved by
disabling depth peeling ("renderer->SetUseDepthPeeling(1);" is commeted out)
 - The second image is the outcome after running the example below unchanged
 - The third image shows what happens if zooming is done. Basically, the
scene is restricted to the left lower part.

It seems like the transformation of the texture is somehow also applied to
the render window?

Any insights on this? (Im running vtk 6 on Windows 8.1)

Kind Regards,
Benjamin

8<--------------------------- Minimal example
-----------------------------------------
#include <vtkActor.h>
#include <vtkConeSource.h>
#include <vtkNew.h>
#include <vtkPNGReader.h>
#include <vtkProperty.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkSTLReader.h>
#include <vtkTexture.h>
#include <vtkTransform.h>

int main(int argc, char** argv)
{
  // Any texture will work. I use a 2 by 2 pixel checkerboard pattern
  vtkNew<vtkPNGReader> pngReader;
  pngReader->SetFileName("texture.png");
  pngReader->Update();

  // Setting up the texture
  // IMPORTANT: Without a transformation on the texture, the bug will not
occur.
  // (You can turn of texture repeating, but I transform to have a
repeating texture)
  vtkNew<vtkTexture> texture;
  texture->SetInputConnection(pngReader->GetOutputPort());
  texture->SetRepeat(true);

  vtkNew<vtkTransform> trans;
  trans->Scale(2.0, 3.0, 1.0);
  texture->SetTransform(trans.Get());

  // Adding a transparent cone. Any geometry will work.
  // IMPORTANT: If the geometry is not transparent, the bug will not occur
  vtkNew<vtkConeSource> coneSrc;
  vtkNew<vtkPolyDataMapper> coneMapper;
  coneMapper->SetInputConnection(coneSrc->GetOutputPort());
  vtkNew<vtkActor> coneActor;
  coneActor->SetMapper(coneMapper.Get());
  coneActor->GetProperty()->SetOpacity(0.5);

  // Create the renderer
  // IMPORTANT: If depth peeling is not enabled, the bug will not occur.
  vtkNew<vtkRenderer> renderer;
  renderer->SetUseDepthPeeling(1);
  renderer->TexturedBackgroundOn();
  renderer->SetBackgroundTexture(texture.Get());
  renderer->AddActor(coneActor.Get());

  // Create the render window
  // IMPORTANT: If AlphaBitPlanes is off, the bug will not occur. (But no
depth peeling either).
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AlphaBitPlanesOn();
  renderWindow->AddRenderer(renderer.Get());

  // Create the interactor and start up
  vtkNew<vtkRenderWindowInteractor> renderInteract;
  renderInteract->SetRenderWindow(renderWindow.Get());
  renderWindow->Render();
  renderInteract->Start();

  return 0;
}
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