iphone - Scale items with iCarousel

Question

I was trying to use iCarousel for one my solutions, I need to achieve something like the image below

It should be exactly the way

iCarouselOptionFadeMin iCarouselOptionFadeMax iCarouselOptionFadeRange iCarouselOptionFadeMinAlpha works using

- (CGFloat)carousel:(iCarousel *)carousel valueForOption:(iCarouselOption)option withDefault:(CGFloat)value

I tried to create a function exactly like

- (CGFloat)alphaForItemWithOffset:(CGFloat)offset

I discovered that it cane be done using offset values, but things are not working me, can any one can help me achieving this?

Thanks.

Answer 1

You can do this via the iCarousel's iCarouselTypeCustom type in the delegate method

- (CATransform3D)carousel:(iCarousel *)carousel itemTransformForOffset:(CGFloat)offset baseTransform:(CATransform3D)transform

Just set the type of the carousel (e.g. in viewDidLoad of the carousel's view controller):

self.carousel.type = iCarouselTypeCustom;

And calculate the transform as you like. I've laid the objects on a hyperbola, and shrink them in addition a bit as they move away from the center. That quite resembles your image, I think:

- (CATransform3D)carousel:(iCarousel *)carousel itemTransformForOffset:(CGFloat)offset baseTransform:(CATransform3D)transform
{
    const CGFloat offsetFactor = [self carousel:carousel valueForOption:iCarouselOptionSpacing withDefault:1.0f]*carousel.itemWidth;

    //The larger these values, as the items move away from the center ...

    //... the faster they move to the back
    const CGFloat zFactor = 150.0f;

    //... the faster they move to the bottom of the screen
    const CGFloat normalFactor = 50.0f;

    //... the faster they shrink
    const CGFloat shrinkFactor = 3.0f;

    //hyperbola
    CGFloat f = sqrtf(offset*offset+1)-1;

    transform = CATransform3DTranslate(transform, offset*offsetFactor, f*normalFactor, f*(-zFactor));
    transform = CATransform3DScale(transform, 1/(f/shrinkFactor+1.0f), 1/(f/shrinkFactor+1.0f), 1.0);
    return transform;
}

and the result:

you can adjust the float constants to your liking.

For moving items around a circle while scaling them just use goniometric functions for translation, then rotate and scale:

- (CGFloat)carousel:(iCarousel *)carousel valueForOption:(iCarouselOption)option withDefault:(CGFloat)value
{
    if (option == iCarouselOptionSpacing)
    {
        return value * 2.0f;
    }
    if(option == iCarouselOptionVisibleItems)
    {
        return 11;
    }
    if(option == iCarouselOptionWrap) return YES;
    return value;
}

- (CATransform3D)carousel:(iCarousel *)carousel itemTransformForOffset:(CGFloat)offset baseTransform:(CATransform3D)transform
{
    const CGFloat radius = [self carousel:carousel valueForOption:iCarouselOptionRadius withDefault:200.0];
    const CGFloat offsetFactor = [self carousel:carousel valueForOption:iCarouselOptionSpacing withDefault:1.0f]*carousel.itemWidth;
    const CGFloat angle = offset*offsetFactor/radius;

    //... the faster they shrink
    const CGFloat shrinkFactor = 2.0f;
    //hyperbola (now only for shrinking purposes)
    CGFloat f = sqrtf(offset*offset+1)-1;


    transform = CATransform3DTranslate(transform, radius*sinf(angle), radius*(1-cosf(angle)), 0.0);
    transform = CATransform3DRotate(transform, angle, 0, 0, 1);
    transform = CATransform3DScale(transform, 1/(f*shrinkFactor+1.0f), 1/(f*shrinkFactor+1.0f), 1.0);
    return transform;
} 

and again, the result:

you can adjust the spacing and the radius in the carousel:valueForOption:withDefault: method.

Enjoy! :)