# FlatVersusGouraud

VTKExamples/Cxx/Rendering/FlatVersusGouraud

### Description¶

Flat and Gouraud shading. Different shading methods can dramatically improve the look of an object represented with polygons. On the top, flat shading uses a constant surface normal across each polygon. On the bottom, Gouraud shading interpolates normals from polygon vertices to give a smoother look.

In this example, the flat and gouraud images for each pair have linked cameras. Rotate and zoom a pair to get a better look at the differences.

Info

See Figure 3-7 in Chapter 3 the VTK Textbook.

Other Languages

See (Python)

Question

If you have a simple question about this example contact us at VTKExamplesProject If your question is more complex and may require extended discussion, please use the VTK Discourse Forum

### Code¶

FlatVersusGouraud.cxx

#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

#include <vtkContourFilter.h>
#include <vtkCylinderSource.h>
#include <vtkOBJReader.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkQuadric.h>
#include <vtkSampleFunction.h>
#include <vtkSphereSource.h>

#include <vtkNamedColors.h>

namespace
{
void CreateSphere(vtkSmartPointer<vtkRenderer>&, bool);
void CreateCylinder(vtkSmartPointer<vtkRenderer>&, bool);
void CreateIsoSurface(vtkSmartPointer<vtkRenderer>&, bool);
void CreateModel(vtkSmartPointer<vtkRenderer>&, bool, char*);
}

int main(int argc, char* argv[])
{

if (argc < 2)
{
std::cout << "Usage: " << argv[0] << " filename" << std::endl;
std::cout << "where: filename is the file cow.obj" << std::endl;
return EXIT_FAILURE;
}

std::vector<vtkSmartPointer<vtkRenderer>> renderers;

// Create the 8 renderers
vtkSmartPointer<vtkRenderer> flatSphereRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(flatSphereRenderer);
vtkSmartPointer<vtkRenderer> flatCylinderRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(flatCylinderRenderer);
vtkSmartPointer<vtkRenderer> flatIsoSurfaceRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(flatIsoSurfaceRenderer);
vtkSmartPointer<vtkRenderer> flatModelRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(flatModelRenderer);
vtkSmartPointer<vtkRenderer> smoothSphereRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(smoothSphereRenderer);
vtkSmartPointer<vtkRenderer> smoothCylinderRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(smoothCylinderRenderer);
vtkSmartPointer<vtkRenderer> smoothIsoSurfaceRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(smoothIsoSurfaceRenderer);
vtkSmartPointer<vtkRenderer> smoothModelRenderer =
vtkSmartPointer<vtkRenderer>::New();
renderers.push_back(smoothModelRenderer);

// Add the actors
CreateSphere(flatSphereRenderer, true);
CreateCylinder(flatCylinderRenderer, true);
CreateIsoSurface(flatIsoSurfaceRenderer, true);
CreateModel(flatModelRenderer, true, argv[1]);

CreateSphere(smoothSphereRenderer, false);
CreateCylinder(smoothCylinderRenderer, false);
CreateIsoSurface(smoothIsoSurfaceRenderer, false);
CreateModel(smoothModelRenderer, false, argv[1]);

vtkSmartPointer<vtkRenderWindow> renderWindow =
vtkSmartPointer<vtkRenderWindow>::New();

// Setup viewports for the renderers
int rendererSize = 256;
unsigned int xGridDimensions = 4;
unsigned int yGridDimensions = 2;
renderWindow->SetSize(rendererSize * xGridDimensions,
rendererSize * yGridDimensions);
for (int row = 0; row < static_cast<int>(yGridDimensions); row++)
{
for (int col = 0; col < static_cast<int>(xGridDimensions); col++)
{
int index = row * xGridDimensions + col;
// (xmin, ymin, xmax, ymax)
double viewport[4] = {
static_cast<double>(col) / xGridDimensions,
static_cast<double>(yGridDimensions - (row + 1)) / yGridDimensions,
static_cast<double>(col + 1) / xGridDimensions,
static_cast<double>(yGridDimensions - row) / yGridDimensions};
renderers[index]->SetViewport(viewport);
}
}

vtkSmartPointer<vtkNamedColors> colors =
vtkSmartPointer<vtkNamedColors>::New();
for (size_t r = 0; r < renderers.size(); ++r)
{
renderers[r]->SetBackground(colors->GetColor3d("SlateGray").GetData());
renderers[r]->GetActiveCamera()->Azimuth(20);
renderers[r]->GetActiveCamera()->Elevation(30);
renderers[r]->ResetCamera();
if (r > 3)
{
renderers[r]->SetActiveCamera(renderers[r - 4]->GetActiveCamera());
}
renderWindow->AddRenderer(renderers[r]);
}
vtkSmartPointer<vtkRenderWindowInteractor> interactor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
interactor->SetRenderWindow(renderWindow);

renderWindow->Render();
interactor->Start();

return EXIT_SUCCESS;
}

namespace
{
void CreateSphere(vtkSmartPointer<vtkRenderer>& renderer, bool flat)
{
vtkSmartPointer<vtkSphereSource> sphere =
vtkSmartPointer<vtkSphereSource>::New();
vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
mapper->SetInputConnection(sphere->GetOutputPort());

vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(mapper);
if (flat)
{
actor->GetProperty()->SetInterpolationToFlat();
}
else
{
actor->GetProperty()->SetInterpolationToGouraud();
}
renderer->AddActor(actor);
}

void CreateCylinder(vtkSmartPointer<vtkRenderer>& renderer, bool flat)
{
vtkSmartPointer<vtkCylinderSource> cylinder =
vtkSmartPointer<vtkCylinderSource>::New();
vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
mapper->SetInputConnection(cylinder->GetOutputPort());

vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(mapper);
if (flat)
{
actor->GetProperty()->SetInterpolationToFlat();
}
else
{
actor->GetProperty()->SetInterpolationToGouraud();
}
renderer->AddActor(actor);
}

void CreateIsoSurface(vtkSmartPointer<vtkRenderer>& renderer, bool flat)
{
double range[2];
// Sample quadric function
vtkSmartPointer<vtkQuadric> quadric = vtkSmartPointer<vtkQuadric>::New();
quadric->SetCoefficients(1, 2, 3, 0, 1, 0, 0, 0, 0, 0);

vtkSmartPointer<vtkSampleFunction> sample =
vtkSmartPointer<vtkSampleFunction>::New();
sample->SetSampleDimensions(25, 25, 25);
sample->SetImplicitFunction(quadric);

// Generate implicit surface
vtkSmartPointer<vtkContourFilter> contour =
vtkSmartPointer<vtkContourFilter>::New();
contour->SetInputConnection(sample->GetOutputPort());
range[0] = 1.0;
range[1] = 6.0;
contour->GenerateValues(5, range);

// Map contour
vtkSmartPointer<vtkPolyDataMapper> contourMapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
contourMapper->SetInputConnection(contour->GetOutputPort());
contourMapper->SetScalarRange(0, 7);

vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(contourMapper);
if (flat)
{
actor->GetProperty()->SetInterpolationToFlat();
}
else
{
actor->GetProperty()->SetInterpolationToGouraud();
}
renderer->AddActor(actor);
return;
}

void CreateModel(vtkSmartPointer<vtkRenderer>& renderer, bool flat,
char* fileName)
{
vtkSmartPointer<vtkOBJReader> reader = vtkSmartPointer<vtkOBJReader>::New();
reader->SetFileName(fileName);

vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
mapper->SetInputConnection(reader->GetOutputPort());

vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(mapper);
if (flat)
{
actor->GetProperty()->SetInterpolationToFlat();
}
else
{
actor->GetProperty()->SetInterpolationToGouraud();
}
renderer->AddActor(actor);
}
}


### CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(FlatVersusGouraud)

find_package(VTK COMPONENTS
vtkCommonColor
vtkCommonDataModel
vtkFiltersCore
vtkFiltersSources
vtkIOGeometry
vtkImagingHybrid
vtkInteractionStyle
vtkRenderingCore
vtkRenderingFreeType
vtkRenderingOpenGL2 QUIET)
if (NOT VTK_FOUND)
message("Skipping FlatVersusGouraud: ${VTK_NOT_FOUND_MESSAGE}") return () endif() message (STATUS "VTK_VERSION:${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
# old system
include(${VTK_USE_FILE}) add_executable(FlatVersusGouraud MACOSX_BUNDLE FlatVersusGouraud.cxx ) target_link_libraries(FlatVersusGouraud PRIVATE${VTK_LIBRARIES})
else ()
# include all components
add_executable(FlatVersusGouraud MACOSX_BUNDLE FlatVersusGouraud.cxx )
target_link_libraries(FlatVersusGouraud PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS FlatVersusGouraud MODULES${VTK_LIBRARIES}
)
endif ()


### Download and Build FlatVersusGouraud¶

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

cd FlatVersusGouraud/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:

./FlatVersusGouraud


WINDOWS USERS

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