How do I get GPUImage animating with a still image source?

Question

I have tried to setup a simple GPUImage environment in a UIViewControler. However, I get a blank screen. I want to animate a property of the swirl filter whilst the source image is kept constant. How can I do this?

I want good performance (> 30 fps) for large-ish images so would ideally like to avoid unnecessary pixel copies back and forth from GPU to CPU.

- (void)viewDidLoad
{
    UIImage *inputImage = [UIImage imageNamed:@"image.jpg"];

    self.stillImageSource = [[GPUImagePicture alloc] initWithImage:inputImage];
    self.swirlFilter = [[GPUImageSwirlFilter alloc] init];
    self.swirlFilter.radius = 0.8;

    self.filteredImageView =
    [[GPUImageView alloc] initWithFrame:
        CGRectMake(0.0, 0.0,
                   self.view.frame.size.width,
                   self.view.frame.size.height)];

    [self.view addSubview:self.filteredImageView];

    // GPUImagePicture -> GPUImageFilter -> GPUImageView
    [self.stillImageSource addTarget:self.swirlFilter];
    [self.swirlFilter addTarget:self.filteredImageView];

    NSAssert(inputImage && _stillImageSource && _swirlFilter && _filteredImageView,
             @"Something unexpected is nil");
}

// Set up a the display link in View Did appear     

- (void) displayLinkDidFire:(CADisplayLink*)displayLink
{
    CGFloat proportion =
    [RSHelper proportionForTime:[[NSDate date] timeIntervalSinceReferenceDate]];

    self.swirlFilter.angle = proportion;

    // Do I need to call some kind of update call here?
}

Answer 1

Ok I found the answer - I was just missing a call to processImage on the GPUImagePicture

- (void) displayLinkDidFire:(CADisplayLink*)displayLink
{
    self.swirlFilter.angle = [Helper calcProportion];
    [self.stillImageSource processImage];
}

GPUImage is actually quite nice to setup and it seams to be faster than CoreImage as it stated in the GPUImage docs. It pains me to use a 3rd party lib over some apple's technology, but I don't see any advantage or CoreImage.