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..

usage

BozoShader PerlinNoise.glsl horse.ply

Cite

Perlin's original Siggraph Paper.

Cite

This shader is inspired by Ken Perlin's Bozo shader.

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

WINDOWS USERS

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