Skip to content

TransparentBackground

vtk-examples/Cxx/Rendering/TransparentBackground


Description

Demonstrates the use of two renderers. Notice that the second (and subsequent) renderers will have a transparent background.

You can manipulate the object in the second layer/renderer whilst the objects in the first layer/renderer form the background.

  • Pressing 0 on the keyboard will let you manipulate the objects in layer 0.
  • Pressing 1 on the keyboard will let you manipulate the objects in layer 1.

Other languages

See (Python)

Question

If you have a question about this example, please use the VTK Discourse Forum

Code

TransparentBackground.cxx

/**
  1. Create a cube and cone source.
  2. Render it with the cube in layer 0 and the cone in layer 1 of the render
  window.
  3. Interact with it.
  4. Notice that the cube and the cone are both visible and the layer 1
  background is transparent.
  5. Pressing '0' on the keyboard will let you manipulate the objects in
  layer 0.
  6. Pressing '1' on the keyboard will let you manipulate the objects in layer 1.
*/

#include <vtkActor.h>
#include <vtkCallbackCommand.h>
#include <vtkConeSource.h>
#include <vtkCubeSource.h>
#include <vtkInteractorObserver.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkRendererCollection.h>

#include <array>
#include <cstdlib>
#include <iomanip>
#include <iostream>

namespace {
void KeypressCallbackFunction(vtkObject* caller, long unsigned int eventId,
                              void* clientData, void* callData);
} // namespace

int main(int argc, char* argv[])
{
  vtkNew<vtkNamedColors> colors;

  vtkNew<vtkCubeSource> cubeSource;
  cubeSource->SetXLength(4.0);
  cubeSource->SetYLength(9.0);
  cubeSource->SetZLength(1.0);
  cubeSource->SetCenter(0.0, 0.0, 0.0);

  // Render the cube
  vtkNew<vtkPolyDataMapper> cubeMapper;
  cubeMapper->SetInputConnection(cubeSource->GetOutputPort());

  vtkNew<vtkActor> cubeActor;
  cubeActor->GetProperty()->SetDiffuseColor(
      colors->GetColor3d("DarkGreen").GetData());
  cubeActor->SetMapper(cubeMapper);

  vtkNew<vtkConeSource> coneSource;
  coneSource->SetCenter(0.0, 0.0, 0.0);
  coneSource->SetHeight(1.0);
  coneSource->SetRadius(0.25);
  coneSource->SetDirection(0.0, 1.0, 0.0);
  coneSource->SetResolution(60);
  coneSource->CappingOn();

  // Render the cone
  vtkNew<vtkPolyDataMapper> coneMapper;
  coneMapper->SetInputConnection(coneSource->GetOutputPort());

  vtkNew<vtkActor> coneActor;
  coneActor->GetProperty()->SetDiffuseColor(
      colors->GetColor3d("DarkTurquoise").GetData());
  // Make the cone slightly transparent for fun
  coneActor->GetProperty()->SetOpacity(0.75);
  coneActor->SetMapper(coneMapper);

  // The renderers, render window and interactor
  std::array<vtkNew<vtkRenderer>, 2> renderers;
  vtkNew<vtkRenderWindow> renWin;
  for (auto&& ren : renderers)
  {
    renWin->AddRenderer(ren);
  }
  renWin->SetSize(800, 800);
  vtkNew<vtkRenderWindowInteractor> iren;
  iren->SetRenderWindow(renWin);

  // Layer 0 - background not transparent
  renderers[0]->SetBackground(colors->GetColor3d("Silver").GetData());
  renderers[0]->AddActor(cubeActor);
  renderers[0]->SetLayer(0);

  // Layer 1 - the background is transparent
  //           so we only see the layer 0 background color
  renderers[1]->AddActor(coneActor);
  renderers[1]->SetBackground(colors->GetColor3d("MidnightBlue").GetData());
  renderers[1]->SetLayer(1);

  // We have two layers
  renWin->SetNumberOfLayers(static_cast<int>(renderers.size()));
  renWin->Render();
  renWin->SetWindowName("TransparentBackground");
  renWin->StereoRenderOff();

  vtkNew<vtkCallbackCommand> keypressCallback;
  keypressCallback->SetCallback(KeypressCallbackFunction);
  iren->AddObserver(vtkCommand::KeyPressEvent, keypressCallback);

  // Interact with the data
  iren->Start();

  return EXIT_SUCCESS;
}

namespace {
void KeypressCallbackFunction(vtkObject* caller,
                              long unsigned int vtkNotUsed(eventId),
                              void* vtkNotUsed(clientData),
                              void* vtkNotUsed(callData))
{
  vtkRenderWindowInteractor* iren =
      static_cast<vtkRenderWindowInteractor*>(caller);
  vtkRendererCollection* renderers = iren->GetRenderWindow()->GetRenderers();
  if (renderers->GetNumberOfItems() < 2)
  {
    std::cerr << "We need at least two renderers, we have only "
              << renderers->GetNumberOfItems() << std::endl;
    return;
  }
  renderers->InitTraversal();
  // Top item
  vtkRenderer* ren0 = renderers->GetNextItem();
  // Bottom item
  vtkRenderer* ren1 = renderers->GetNextItem();

  std::string key = iren->GetKeySym();

  if (key == "0")
  {
    iren->GetRenderWindow()
        ->GetInteractor()
        ->GetInteractorStyle()
        ->SetDefaultRenderer(ren0);
    ren0->InteractiveOn();
    ren1->InteractiveOff();
  }
  if (key == "1")
  {
    iren->GetRenderWindow()
        ->GetInteractor()
        ->GetInteractorStyle()
        ->SetDefaultRenderer(ren1);
    ren0->InteractiveOff();
    ren1->InteractiveOn();
  }
}
} // namespace

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(TransparentBackground)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonCore
  vtkFiltersSources
  vtkInteractionStyle
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  vtkRenderingOpenGL2
  QUIET
)

if (NOT VTK_FOUND)
  message("Skipping TransparentBackground: ${VTK_NOT_FOUND_MESSAGE}")
  return ()
endif()
message (STATUS "VTK_VERSION: ${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
  # old system
  include(${VTK_USE_FILE})
  add_executable(TransparentBackground MACOSX_BUNDLE TransparentBackground.cxx )
  target_link_libraries(TransparentBackground PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(TransparentBackground MACOSX_BUNDLE TransparentBackground.cxx )
  target_link_libraries(TransparentBackground PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS TransparentBackground
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build TransparentBackground

Click here to download TransparentBackground and its CMakeLists.txt file. Once the tarball TransparentBackground.tar has been downloaded and extracted,

cd TransparentBackground/build

If VTK is installed:

cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

make

and run it:

./TransparentBackground

WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.