Why are the cells with reversed normal always black even the Backface property got set?

Support
1

Hello,I need to set the one face of the cell with reversed normal blue,and the another face to red.Test code like this:

#include <vtkVersion.h>
#include <vtkNew.h>

#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkPolyData.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkSphereSource.h>

int main(int argc, char *argv[])
{
	vtkNew<vtkSphereSource> source;
	source->SetPhiResolution(10);
	source->SetThetaResolution(10);
	source->Update();

	vtkNew<vtkPolyDataMapper> mapper;
	mapper->SetInputConnection(source->GetOutputPort());
	mapper->Update();

	vtkNew<vtkActor> actor;
	actor->SetMapper(mapper);

	vtkNew<vtkRenderer> ren;
	vtkNew<vtkRenderWindow> renWin;
	renWin->AddRenderer(ren);
	vtkNew<vtkRenderWindowInteractor> iren;
	iren->SetRenderWindow(renWin);

	ren->AddActor(actor);
	ren->SetBackground(.2, .3, .4);

	for (int id = 0; id < 100; id++)
	{
		dynamic_cast<vtkPolyData*>(actor->GetMapper()->GetInput())->ReverseCell(id);
	}

	actor->GetProperty()->EdgeVisibilityOn();
	actor->GetProperty()->SetColor(0, 0, 1);
	actor->GetProperty()->SetEdgeColor(1, 1, 1);

	vtkProperty *bp = vtkProperty::New();
	bp->SetColor(0, 1, 0);
	actor->SetBackfaceProperty(bp);


	renWin->Render();
	iren->Start();

	return EXIT_SUCCESS;
}

But two faces of this kind of cell are always show black like this,

Workspace 1_1596
Workspace 1_1596795×672 58.1 KB

even the back face property got set.

So,how to set the different colors for each face of the cell with reversed normal?

2

They are black because the polygon winding and surface normal direction are inconsistent. If you want colored cells then a better way to do it is by adding a scalar array to the celldata.

3

Hello,

Please, take a look at this: Is it possible to set the different color for front/back face of a cell?

take care,

PC