[vtkusers] Problem getting opacity values to work

[shawn b]

I was wondering if anyone could offer some advice as to what I am doing 
wrong with a program that I am working on.  I am trying to get 1 image to 
gradually fade out and another image to gradually fade in.  I am using 
vtkImageBlend and adjusting the opacity of the 2 bitmaps to try and achieve 
this effect.

However what I am getting as a result right now is a quick switch from 1 
image to the other without any fading.  The first image stays up until the 
opacity hits 0 then the second image shows up on the screen.  I think it 
might be a problem with updating the properties of the different elements 
that are being displayed but if that is the case then why is the screen 
switching from one image to the other when the opacity hits 0.

Any advice as to what I can do to achieve this gradual fade would be very 
welcome.  This is the source code for the program that I described above:


int main()
{
	int width = 10;
	int height = 10;
	int i = 0;
	float opacity1 = 1;
	float opacity2 = 0;
	double test_opac1 = 1;
	double test_opac2 = 0;

	// Path to input file
	char* filename = "D:\\shawn\\alafia40.bmp";
	char* filename2 = "D:\\shawn\\alafia63.bmp";

	vtkImageBlend *test = vtkImageBlend::New();


	vtkCamera *camera = vtkCamera::New();

	vtkPlaneSource *plane = vtkPlaneSource::New();
	vtkPlaneSource *plane2 = vtkPlaneSource::New();

	vtkBMPReader *bmp = vtkBMPReader::New();
	vtkBMPReader *bmp2 = vtkBMPReader::New();

	vtkTexture *texture = vtkTexture::New();
	vtkTexture *texture2 = vtkTexture::New();
	vtkTexture *TextureTest = vtkTexture::New();

	vtkPolyDataMapper *planeMapper = vtkPolyDataMapper::New();
	vtkPolyDataMapper *planeMapper2 = vtkPolyDataMapper::New();

	vtkActor *planeActor = vtkActor::New();
	vtkActor *planeActor2 = vtkActor::New();

	camera->SetPosition(0,0,2);

	// Read in bitmap
	bmp->SetFileName(filename);
	bmp2->SetFileName(filename2);

        // Set bitmaps as input for vtkImageBlend variable
	test->AddInput(bmp->GetOutput());
	test->AddInput(bmp2->GetOutput());


	// Set the vtkImageBlend variable as the input for the texture
	TextureTest->SetInput( test->GetOutput() );



	// Set resolution for the plane
	plane->SetResolution( width, height);

	//Map the plane
        planeMapper->SetInput( plane->GetOutput() );

        // Set the texutre and mapper for the actor
	planeActor->SetMapper( planeMapper );
	planeActor->SetTexture( TextureTest );

	// create a renderer and assign actors to it
	vtkRenderer *renderer1= vtkRenderer::New();
	renderer1->AddActor( planeActor );
	renderer1->SetBackground( 0, 0, 0 );

        //create render window and assign renderer to it
        vtkRenderWindow *renderWin = vtkRenderWindow::New();
	renderWin->AddRenderer( renderer1 );
	renderWin->SetSize( 800, 600 );

        //Set initial opacities of actor and bitmaps
	planeActor->GetProperty()->SetOpacity(opacity1);
	test->SetOpacity(1,test_opac1);
	test->SetOpacity(2,test_opac2);
	renderWin->Start();

        //for loop to test the fading
        //slowly lower the opacity of 1 image and lower opacity
        //of the other image
	for (i = 0; i < 1400; ++i)
        {
        // render the image
	test_opac1 = (test_opac1 - (i/1000));
	test_opac2 = (test_opac2 + (i/1000));
	test->SetOpacity(1,test_opac1);
	test->SetOpacity(2,test_opac2);

        renderWin->Render();


	renderer1->SetActiveCamera(camera);
	}



	return 0;

}

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