[vtkusers] problem met while using vtkImageWriter

[Zhan Zhang]

Hi,

I have a problem while using the vtkImageWriter in an updating fashion to write a sequence of images from a rendering window. Specifically, I generate a sequence of renderings in a
render window, then, for each rendering, I get the image from the render Window, and save it using vtkImageWriter. But all the saved image files contain the same image--the very first rendering. Could someone tell me how to correct it? Bellow is my code segment, I wrote it within VC++ running on Win2000. 

	
	//define a renderer ren_cow
	vtkRenderer *ren_cow;
	ren_cow=vtkRenderer::New();
	ren_cow->AddActor(Actor);

	//define a render window
	vtkRenderWindow *renWin_cow;
	renWin_cow=vtkRenderWindow::New();
	renWin_cow->AddRenderer(ren_cow);
	
	//define a WindowToImageFilter	
	vtkWindowToImageFilter *w2i;
	w2i=vtkWindowToImageFilter::New();
	w2i->SetInput(renWin_cow);

	//define an ImageLuminance filter
	vtkImageLuminance *c2g;
	c2g=vtkImageLuminance::New();
	c2g->SetInput(w2i->GetOutput());
	
	//define an ImageWriter 
	vtkImageWriter *writer;
	writer=vtkImageWriter::New();
	writer->SetInput(c2g->GetOutput());

	
	//generate a sequence of views by change camera azimuth
	//then for each view write it to an file
	for (i=0; i<360; i++){		
		renWin_cow->Render();
		//define file name
		sprintf(image_file_name,"C:\\cow%d", i);

		writer->SetFileName(image_file_name);
		writer->Write();

		//update camera
		ren_cow->GetActiveCamera()->Azimuth(1);
	}

the sequence of renderings shows perfectly in the render window, and I also get a series of image files as cow0, cow1, cow2.....

but these image files are all same as cow0. I change the vtkImageWriter to vtkJPEGWriter, same problem.
I also try to update before using Write() method, such as
w2i->Update();
c2g->Update();
also, end up with same problem.

Hopefully someone can help point out where the problem is. Thanks a lot.

Zhan