ColorByNormal
VTKExamples/Cxx/Shaders/ColorByNormal
Description¶
This example modifies the shader to color based on model normal To do this we have to modify the vertex shader to pass the normal in model coordinates through to the fragment shader. By default the normal is converted to View coordinates and then passed on. We keep that, but add a varying for the original normal. Then we modify the fragment shader to set the diffuse color based on that normal.
Cite
This example was inspired by the test TestUserShader.
Code¶
ColorByNormal.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 <vtkSmartPointer.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 namespace { vtkSmartPointer<vtkPolyData> ReadPolyData(const char* fileName); } //---------------------------------------------------------------------------- int main(int argc, char* argv[]) { auto polyData = ReadPolyData(argc > 1 ? argv[1] : ""); 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); auto norms = vtkSmartPointer<vtkTriangleMeshPointNormals>::New(); norms->SetInputData(polyData); mapper->SetInputConnection(norms->GetOutputPort()); actor->SetMapper(mapper); actor->GetProperty()->SetAmbientColor(0.2, 0.2, 1.0); actor->GetProperty()->SetDiffuseColor(1.0, 0.65, 0.7); actor->GetProperty()->SetSpecularColor(1.0, 1.0, 1.0); actor->GetProperty()->SetSpecular(0.5); actor->GetProperty()->SetDiffuse(0.7); actor->GetProperty()->SetAmbient(0.5); actor->GetProperty()->SetSpecularPower(20.0); actor->GetProperty()->SetOpacity(1.0); // Modify the shader to color based on model normal // To do this we have to modify the vertex shader // to pass the normal in model coordinates // through to the fragment shader. By default the normal // is converted to View coordinates and then passed on. // We keep that, but add a varying for the original normal. // Then we modify the fragment shader to set the diffuse color // based on that normal. First lets modify the vertex // shader #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 " varying vec3 myNormalMCVSOutput;\n", // but we add this 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 " varying vec3 myNormalMCVSOutput;\n", // but we add this 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 " myNormalMCVSOutput = normalMC;\n", // but we add this 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 " myNormalMCVSOutput = normalMC;\n", // but we add this false // only do it once ); #endif #if USE_SHADER_PROPERTIES sp->AddVertexShaderReplacement( "//VTK::Color::Impl", // dummy replacement for testing clear method true, "VTK::Color::Impl\n", false); #else mapper->AddShaderReplacement( vtkShader::Vertex, "//VTK::Color::Impl", // dummy replacement for testing clear method true, "VTK::Color::Impl\n", false); #endif #if USE_SHADER_PROPERTIES sp->ClearVertexShaderReplacement("//VTK::Color::Impl", true); #else mapper->ClearShaderReplacement( vtkShader::Vertex, // clear our dummy replacement "//VTK::Color::Impl", true); #endif // now modify the fragment shader #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 vec3 myNormalMCVSOutput;\n", // but we add this 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 vec3 myNormalMCVSOutput;\n", // but we add this false // only do it once ); #endif #if USE_SHADER_PROPERTIES sp->AddFragmentShaderReplacement( "//VTK::Normal::Impl", // replace the normal block true, // before the standard replacements "//VTK::Normal::Impl\n" // we still want the default calc " diffuseColor = abs(myNormalMCVSOutput);\n", // but we add this false // only do it once ); #else mapper->AddShaderReplacement( vtkShader::Fragment, // in the fragment shader "//VTK::Normal::Impl", // replace the normal block true, // before the standard replacements "//VTK::Normal::Impl\n" // we still want the default calc " diffuseColor = abs(myNormalMCVSOutput);\n", // but we add this false // only do it once ); #endif renderWindow->Render(); renderer->GetActiveCamera()->SetPosition(1.0, 1.0, -1.0); renderer->GetActiveCamera()->SetFocalPoint(0, 1, 0); renderer->GetActiveCamera()->SetViewUp(0, 1, 0); renderer->GetActiveCamera()->Elevation(30.0); renderer->ResetCamera(); renderer->GetActiveCamera()->Zoom(1.3); renderWindow->Render(); renderWindow->SetWindowName("ColorByNormal"); renderWindow->Render(); interactor->Start(); 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(ColorByNormal) find_package(VTK COMPONENTS vtkCommonColor vtkCommonCore vtkFiltersCore vtkFiltersSources vtkIOGeometry vtkIOLegacy vtkIOPLY vtkIOXML vtkInteractionStyle vtkRenderingContextOpenGL2 vtkRenderingCore vtkRenderingFreeType vtkRenderingGL2PSOpenGL2 vtkRenderingOpenGL2 QUIET) if (NOT VTK_FOUND) message("Skipping ColorByNormal: ${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(ColorByNormal MACOSX_BUNDLE ColorByNormal.cxx ) target_link_libraries(ColorByNormal PRIVATE ${VTK_LIBRARIES}) else () # include all components add_executable(ColorByNormal MACOSX_BUNDLE ColorByNormal.cxx ) target_link_libraries(ColorByNormal PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS ColorByNormal MODULES ${VTK_LIBRARIES} ) endif ()
Download and Build ColorByNormal¶
Click here to download ColorByNormal and its CMakeLists.txt file. Once the tarball ColorByNormal.tar has been downloaded and extracted,
cd ColorByNormal/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:
./ColorByNormal
WINDOWS USERS
Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.