BozoShader

VTKEx/Cxx/Shaders/BozoShader

Description¶

This example shows how to add user functions to a VTK shader. The example's fragment shader uses an implementation of Ken Perlin's noise function. Perlin received a Technical Achievement Academy Award for his work procedural texture.

The shader code contains a variable "k" that controls the frequency of the noisy colors. The default value will provide reasonable results for all polydata.

The file for the shader code is here..

Code¶

BozoShader.cxx

#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkNamedColors.h>
#include <vtkOpenGLPolyDataMapper.h>
#include <vtkPolyDataNormals.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkShaderProgram.h>
#include <vtkSmartPointer.h>
#include <vtkTransform.h>
#include <vtkTransformPolyDataFilter.h>
#include <vtkTriangleFilter.h>
#include <vtkTriangleMeshPointNormals.h>
#include <vtkVersion.h>

#include <vtkBYUReader.h>
#include <vtkOBJReader.h>
#include <vtkPLYReader.h>
#include <vtkPolyDataReader.h>
#include <vtkSTLReader.h>
#include <vtkSphereSource.h>
#include <vtkXMLPolyDataReader.h>
#include <vtksys/SystemTools.hxx>

#if VTK_VERSION_NUMBER >= 89000000000ULL
#define USE_SHADER_PROPERTIES 1
#include <vtkShaderProperty.h>
#endif

#include <fstream>
#include <sstream>

namespace {
// -----------------------------------------------------------------------
// Update a uniform in the shader for each render. We do this with a
// callback for the UpdateShaderEvent
class vtkShaderCallback : public vtkCommand
{
public:
  static vtkShaderCallback* New()
  {
    return new vtkShaderCallback;
  }
  vtkRenderer* Renderer;
  float k;
  void Execute(vtkObject*, unsigned long, void* calldata) override
  {
    vtkShaderProgram* program = reinterpret_cast<vtkShaderProgram*>(calldata);
    if (program)
    {
      program->SetUniformf("k", k);
    }
  }
  void Print(std::ostream& os)
  {
    os << "k: " << k << std::endl;
  }

  vtkShaderCallback()
  {
    this->Renderer = nullptr;
    this->k = 5;
  }
};
} // namespace

namespace {
vtkSmartPointer<vtkPolyData> ReadPolyData(const char* fileName);
}

//----------------------------------------------------------------------------
int main(int argc, char* argv[])
{
  if (argc < 2)
  {
    std::cout << "Usage: " << argv[0] << " PerlnNoise.glsl "
              << "[polydataFile] "
              << "[k(5)]" << std::endl;
    return EXIT_FAILURE;
  }
  auto polyData = ReadPolyData(argc > 2 ? argv[2] : "");

  std::ifstream shaderFile(argv[1]);
  std::ostringstream shaderCode;
  shaderCode << shaderFile.rdbuf();

  // Create a transform to rescale model
  double center[3];
  polyData->GetCenter(center);
  double bounds[6];
  polyData->GetBounds(bounds);
  double maxBound =
      std::max(std::max(bounds[1] - bounds[0], bounds[3] - bounds[2]),
               bounds[5] - bounds[4]);

  auto colors = vtkSmartPointer<vtkNamedColors>::New();

  auto actor = vtkSmartPointer<vtkActor>::New();
  auto renderer = vtkSmartPointer<vtkRenderer>::New();
  auto mapper = vtkSmartPointer<vtkOpenGLPolyDataMapper>::New();
  renderer->SetBackground(colors->GetColor3d("SlateGray").GetData());

  auto renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->SetSize(640, 480);
  renderWindow->AddRenderer(renderer);
  renderer->AddActor(actor);

  auto interactor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
  interactor->SetRenderWindow(renderWindow);

  // Rescale polydata to [-1,1]
  auto userTransform = vtkSmartPointer<vtkTransform>::New();
  userTransform->Translate(-center[0], -center[1], -center[2]);
  userTransform->Scale(1.0 / maxBound, 1.0 / maxBound, 1.0 / maxBound);
  auto transform = vtkSmartPointer<vtkTransformPolyDataFilter>::New();
  transform->SetTransform(userTransform);
  transform->SetInputData(polyData);

  auto triangles = vtkSmartPointer<vtkTriangleFilter>::New();
  triangles->SetInputConnection(transform->GetOutputPort());

  auto norms = vtkSmartPointer<vtkTriangleMeshPointNormals>::New();
  norms->SetInputConnection(triangles->GetOutputPort());

  mapper->SetInputConnection(norms->GetOutputPort());
  mapper->ScalarVisibilityOff();

  actor->SetMapper(mapper);
  actor->GetProperty()->SetAmbientColor(0.2, 0.2, 0.2);
  actor->GetProperty()->SetDiffuseColor(1.0, 1.0, 1.0);
  actor->GetProperty()->SetSpecularColor(1.0, 1.0, 1.0);
  actor->GetProperty()->SetSpecular(0.5);
  actor->GetProperty()->SetDiffuse(0.7);
  actor->GetProperty()->SetAmbient(0.1);
  actor->GetProperty()->SetSpecularPower(100.0);
  actor->GetProperty()->SetOpacity(1.0);

  // Modify the vertex shader to pass the position of the vertex
#if USE_SHADER_PROPERTIES
  vtkShaderProperty* sp = actor->GetShaderProperty();
  sp->AddVertexShaderReplacement(
      "//VTK::Normal::Dec",  // replace the normal block
      true,                  // before the standard replacements
      "//VTK::Normal::Dec\n" // we still want the default
      "  out vec4 myVertexMC;\n",
      false // only do it once
  );
#else
  mapper->AddShaderReplacement(
      vtkShader::Vertex,
      "//VTK::Normal::Dec",  // replace the normal block
      true,                  // before the standard replacements
      "//VTK::Normal::Dec\n" // we still want the default
      "  out vec4 myVertexMC;\n",
      false // only do it once
  );
#endif
#if USE_SHADER_PROPERTIES
  sp->AddVertexShaderReplacement(
      "//VTK::Normal::Impl",  // replace the normal block
      true,                   // before the standard replacements
      "//VTK::Normal::Impl\n" // we still want the default
      "  myVertexMC = vertexMC;\n",
      false // only do it once
  );
#else
  mapper->AddShaderReplacement(
      vtkShader::Vertex,
      "//VTK::Normal::Impl",  // replace the normal block
      true,                   // before the standard replacements
      "//VTK::Normal::Impl\n" // we still want the default
      "  myVertexMC = vertexMC;\n",
      false // only do it once
  );
#endif

  // Add the code to generate noise
  // These functions need to be defined outside of main. Use the System::Dec
  // to declare and implement
#if USE_SHADER_PROPERTIES
  sp->AddFragmentShaderReplacement("//VTK::System::Dec",
                                   false, // before the standard replacements
                                   shaderCode.str(),
                                   false // only do it once
  );

#else
  mapper->AddShaderReplacement(vtkShader::Fragment, "//VTK::System::Dec",
                               false, // before the standard replacements
                               shaderCode.str(),
                               false // only do it once
  );
#endif

  // Define varying and uniforms for the fragment shader here
#if USE_SHADER_PROPERTIES
  sp->AddFragmentShaderReplacement(
      "//VTK::Normal::Dec",  // replace the normal block
      true,                  // before the standard replacements
      "//VTK::Normal::Dec\n" // we still want the default
      "  varying vec4 myVertexMC;\n"
      "  uniform float k = 1.0;\n",
      false // only do it once
  );
#else
  mapper->AddShaderReplacement(
      vtkShader::Fragment,   // in the fragment shader
      "//VTK::Normal::Dec",  // replace the normal block
      true,                  // before the standard replacements
      "//VTK::Normal::Dec\n" // we still want the default
      "  varying vec4 myVertexMC;\n"
      "  uniform float k = 1.0;\n",
      false // only do it once
  );
#endif

#if USE_SHADER_PROPERTIES
  sp->AddFragmentShaderReplacement(
      "//VTK::Light::Impl",  // replace the light block
      false,                 // after the standard replacements
      "//VTK::Light::Impl\n" // we still want the default calc
      "#define pnoise(x) ((noise(x) + 1.0) / 2.0)\n"
      "  vec3 noisyColor;\n"
      "  noisyColor.r = noise(k * 10.0 * myVertexMC);\n"
      "  noisyColor.g = noise(k * 11.0 * myVertexMC);\n"
      "  noisyColor.b = noise(k * 12.0 * myVertexMC);\n"
      "  /* map ranges of noise values into different colors */\n"
      "  int i;\n"
      "  float lowerValue = .3;\n"
      "  float upperValue = .6;\n"
      "  for ( i=0; i<3; i+=1)\n"
      "  {\n"
      "    noisyColor[i] = (noisyColor[i] + 1.0) / 2.0;\n"
      "    if (noisyColor[i] < lowerValue) \n"
      "    {\n"
      "      noisyColor[i] = lowerValue;\n"
      "    }\n"
      "    else\n"
      "    {\n"
      "      if (noisyColor[i] < upperValue)\n"
      "      {\n"
      "        noisyColor[i] = upperValue;\n"
      "      }\n"
      "      else\n"
      "      {\n"
      "        noisyColor[i] = 1.0;\n"
      "      }\n"
      "    }\n"
      "  }\n"
      "  fragOutput0.rgb = opacity * vec3(ambientColor + noisyColor * diffuse "
      "+ specular);\n"
      "  fragOutput0.a = opacity;\n",
      false // only do it once
  );
#else
  mapper->AddShaderReplacement(
      vtkShader::Fragment,   // in the fragment shader
      "//VTK::Light::Impl",  // replace the light block
      false,                 // after the standard replacements
      "//VTK::Light::Impl\n" // we still want the default calc
      "#define pnoise(x) ((noise(x) + 1.0) / 2.0)\n"
      "  vec3 noisyColor;\n"
      "  noisyColor.r = noise(k * 10.0 * myVertexMC);\n"
      "  noisyColor.g = noise(k * 11.0 * myVertexMC);\n"
      "  noisyColor.b = noise(k * 12.0 * myVertexMC);\n"
      "  /* map ranges of noise values into different colors */\n"
      "  int i;\n"
      "  float lowerValue = .3;\n"
      "  float upperValue = .6;\n"
      "  for ( i=0; i<3; i+=1)\n"
      "  {\n"
      "    noisyColor[i] = (noisyColor[i] + 1.0) / 2.0;\n"
      "    if (noisyColor[i] < lowerValue) \n"
      "    {\n"
      "      noisyColor[i] = lowerValue;\n"
      "    }\n"
      "    else\n"
      "    {\n"
      "      if (noisyColor[i] < upperValue)\n"
      "      {\n"
      "        noisyColor[i] = upperValue;\n"
      "      }\n"
      "      else\n"
      "      {\n"
      "        noisyColor[i] = 1.0;\n"
      "      }\n"
      "    }\n"
      "  }\n"
      "  fragOutput0.rgb = opacity * vec3(ambientColor + noisyColor * diffuse "
      "+ specular);\n"
      "  fragOutput0.a = opacity;\n",
      false // only do it once
  );
#endif
  auto myCallback = vtkSmartPointer<vtkShaderCallback>::New();
  myCallback->Renderer = renderer;
  if (argc == 2 || argc == 3)
  {
    myCallback->k = 1;
  }
  else
  {
    myCallback->k = atof(argv[3]);
  }
  std::cout << "Input: " << (argc > 2 ? argv[2] : "Generated Sphere")
            << std::endl;
  myCallback->Print(std::cout);
  mapper->AddObserver(vtkCommand::UpdateShaderEvent, myCallback);

  renderWindow->Render();
  renderer->GetActiveCamera()->SetPosition(-.3, 0, .08);
  renderer->GetActiveCamera()->SetFocalPoint(0, 0, 0);
  renderer->GetActiveCamera()->SetViewUp(.26, 0.0, .96);
  renderer->ResetCamera();
  renderer->GetActiveCamera()->Zoom(1.5);
  renderWindow->Render();
  renderWindow->SetWindowName("BozoShader");
  renderWindow->Render();
  interactor->Start();

  transform->GetOutput()->GetBounds(bounds);
  std::cout << "Range: "
            << " x " << bounds[1] - bounds[0] << " y " << bounds[3] - bounds[2]
            << " y " << bounds[5] - bounds[4] << std::endl;
  return EXIT_SUCCESS;
}

namespace {
vtkSmartPointer<vtkPolyData> ReadPolyData(const char* fileName)
{
  vtkSmartPointer<vtkPolyData> polyData;
  std::string extension =
      vtksys::SystemTools::GetFilenameExtension(std::string(fileName));
  if (extension == ".ply")
  {
    auto reader = vtkSmartPointer<vtkPLYReader>::New();
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".vtp")
  {
    auto reader = vtkSmartPointer<vtkXMLPolyDataReader>::New();
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".obj")
  {
    auto reader = vtkSmartPointer<vtkOBJReader>::New();
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".stl")
  {
    auto reader = vtkSmartPointer<vtkSTLReader>::New();
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".vtk")
  {
    auto reader = vtkSmartPointer<vtkPolyDataReader>::New();
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".g")
  {
    auto reader = vtkSmartPointer<vtkBYUReader>::New();
    reader->SetGeometryFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else
  {
    auto source = vtkSmartPointer<vtkSphereSource>::New();
    source->SetPhiResolution(25);
    source->SetThetaResolution(25);
    source->Update();
    polyData = source->GetOutput();
  }
  return polyData;
}
} // namespace

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(BozoShader)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonCore
  vtkCommonTransforms
  vtkFiltersCore
  vtkFiltersGeneral
  vtkFiltersSources
  vtkIOGeometry
  vtkIOLegacy
  vtkIOPLY
  vtkIOXML
  vtkInteractionStyle
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  vtkRenderingOpenGL2 QUIET)
if (NOT VTK_FOUND)
  message("Skipping BozoShader: ${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(BozoShader MACOSX_BUNDLE BozoShader.cxx )
  target_link_libraries(BozoShader PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(BozoShader MACOSX_BUNDLE BozoShader.cxx )
  target_link_libraries(BozoShader PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS BozoShader
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build BozoShader¶

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

cd BozoShader/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:

./BozoShader