Widget “flip” behavior in Core Animation/Cocoa

Question

I'm trying to make a Card class that duplicates the behavior of Dashboard widgets in that you can put controls or images or whatever on two sides of the card and flip between them.

Layer backed views have a transform property, but altering that doesn't do what I would expect it to do (rotating the layer around the y axis folds it off to the left side).

I was pointed to some undocumented features and an .h file named cgsprivate.h, but I'm wondering if there is an official way to do this? This software would have to be shipped and I'd hate to see it fail later because the Apple guys pull it in 10.6.

Anyone have any idea how to do this? It's so weird to me that a simple widget thing would be so hard to do in Core Animation.

Thanks in advance!

EDIT: I can accomplish this behavior with images that are on layers, but I don't know how to get more advanced controls/views/whatever on the layers. The card example uses images.

Answer 1

If you are able to do this with images, perhaps you can keep all of your controls in an NSView object (as usual), and then render the NSView into a bitmap image using cacheDisplayInRect:toBitmapImageRep: just prior to executing the flip effect. The steps would be:

1. Render the NSView to a bitmap
2. Display that bitmap in a layer suitable for the flip effect
3. Hide the NSView and expose the image layer
4. Perform the flip effect

Answer 2

I know this is late but Apple has an example project here that may be of help to anyone still stumbling upon this question.

https://developer.apple.com/library/mac/#samplecode/ImageTransition/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010277

Answer 3

Using Core Animation like e.James outlined...Note, this is using garbage collection and a hosted layer:

#import "AnimationWindows.h"

@interface AnimationFlipWindow (PrivateMethods)

NSRect RectToScreen(NSRect aRect, NSView *aView);
NSRect RectFromScreen(NSRect aRect, NSView *aView);
NSRect RectFromViewToView(NSRect aRect, NSView *fromView, NSView *toView);

@end

#pragma mark -

@implementation AnimationFlipWindow

@synthesize flipForward = _flipForward;

- (id) init {

    if ( self = [super init] ) { 
        _flipForward = YES; 
    }

    return self;
}

- (void) finalize {

    // Hint to GC for cleanup
    [[NSGarbageCollector defaultCollector] collectIfNeeded];
    [super finalize];
}

- (void) flip:(NSWindow *)activeWindow 
       toBack:(NSWindow *)targetWindow {

    CGFloat duration = 1.0f * (activeWindow.currentEvent.modifierFlags & NSShiftKeyMask ? 10.0 : 1.0);
    CGFloat zDistance = 1500.0f;

    NSView *activeView = [activeWindow.contentView superview];
    NSView *targetView = [targetWindow.contentView superview];

    // Create an animation window
    CGFloat maxWidth  = MAX(NSWidth(activeWindow.frame), NSWidth(targetWindow.frame)) + 500;
    CGFloat maxHeight = MAX(NSHeight(activeWindow.frame), NSHeight(targetWindow.frame)) + 500;

    CGRect animationFrame = CGRectMake(NSMidX(activeWindow.frame) - (maxWidth / 2), 
                                       NSMidY(activeWindow.frame) - (maxHeight / 2), 
                                       maxWidth, 
                                       maxHeight);

    mAnimationWindow = [NSWindow initForAnimation:NSRectFromCGRect(animationFrame)];

    // Add a touch of perspective
    CATransform3D transform = CATransform3DIdentity; 
    transform.m34 = -1.0 / zDistance;
    [mAnimationWindow.contentView layer].sublayerTransform = transform;

    // Relocate target window near active window
    CGRect targetFrame = CGRectMake(NSMidX(activeWindow.frame) - (NSWidth(targetWindow.frame) / 2 ), 
                                    NSMaxY(activeWindow.frame) - NSHeight(targetWindow.frame),
                                    NSWidth(targetWindow.frame),
                                    NSHeight(targetWindow.frame));

    [targetWindow setFrame:NSRectFromCGRect(targetFrame) display:NO];

    mTargetWindow = targetWindow;

    // New Active/Target Layers
    [CATransaction begin];
    CALayer *activeWindowLayer = [activeView layerFromWindow];
    CALayer *targetWindowLayer = [targetView layerFromWindow];
    [CATransaction commit];

    activeWindowLayer.frame = NSRectToCGRect(RectFromViewToView(activeView.frame, activeView, [mAnimationWindow contentView]));
    targetWindowLayer.frame = NSRectToCGRect(RectFromViewToView(targetView.frame, targetView, [mAnimationWindow contentView]));

    [CATransaction begin];
    [[mAnimationWindow.contentView layer] addSublayer:activeWindowLayer];
    [CATransaction commit];

    [mAnimationWindow orderFront:nil];  

    [CATransaction begin];
    [[mAnimationWindow.contentView layer] addSublayer:targetWindowLayer];
    [CATransaction commit];

    // Animate our new layers
    [CATransaction begin];
    CAAnimation *activeAnim = [CAAnimation animationWithDuration:(duration * 0.5) flip:YES forward:_flipForward];
    CAAnimation *targetAnim = [CAAnimation animationWithDuration:(duration * 0.5) flip:NO  forward:_flipForward];
    [CATransaction commit];

    targetAnim.delegate = self;
    [activeWindow orderOut:nil];

    [CATransaction begin];
    [activeWindowLayer addAnimation:activeAnim forKey:@"flip"];
    [targetWindowLayer addAnimation:targetAnim forKey:@"flip"];
    [CATransaction commit];
}

- (void) animationDidStop:(CAAnimation *)animation finished:(BOOL)flag {

    if (flag) {
        [mTargetWindow makeKeyAndOrderFront:nil];
        [mAnimationWindow orderOut:nil];

        mTargetWindow = nil;
        mAnimationWindow = nil;
    }
}

#pragma mark PrivateMethods:

NSRect RectToScreen(NSRect aRect, NSView *aView) {
    aRect = [aView convertRect:aRect toView:nil];
    aRect.origin = [aView.window convertBaseToScreen:aRect.origin];
    return aRect;
}

NSRect RectFromScreen(NSRect aRect, NSView *aView) {
    aRect.origin = [aView.window convertScreenToBase:aRect.origin];
    aRect = [aView convertRect:aRect fromView:nil];
    return aRect;
}

NSRect RectFromViewToView(NSRect aRect, NSView *fromView, NSView *toView) {

    aRect = RectToScreen(aRect, fromView);
    aRect = RectFromScreen(aRect, toView);

    return aRect;
}

@end

#pragma mark -
#pragma mark CategoryMethods:

@implementation CAAnimation (AnimationFlipWindow)

+ (CAAnimation *) animationWithDuration:(CGFloat)time flip:(BOOL)bFlip forward:(BOOL)forwardFlip{

    CABasicAnimation *flipAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.y"];

    CGFloat startValue, endValue;

    if ( forwardFlip ) {
        startValue = bFlip ? 0.0f : -M_PI;
        endValue = bFlip ? M_PI : 0.0f;
    } else {
        startValue = bFlip ? 0.0f : M_PI;
        endValue = bFlip ? -M_PI : 0.0f;
    }

    flipAnimation.fromValue = [NSNumber numberWithDouble:startValue];
    flipAnimation.toValue = [NSNumber numberWithDouble:endValue];

    CABasicAnimation *shrinkAnimation = [CABasicAnimation animationWithKeyPath:@"transform.scale"];
    shrinkAnimation.toValue = [NSNumber numberWithFloat:1.3f];
    shrinkAnimation.duration = time * 0.5;
    shrinkAnimation.autoreverses = YES;

    CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
    animationGroup.animations = [NSArray arrayWithObjects:flipAnimation, shrinkAnimation, nil];
    animationGroup.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    animationGroup.duration = time;
    animationGroup.fillMode = kCAFillModeForwards;
    animationGroup.removedOnCompletion = NO;

    return animationGroup;
}

@end

#pragma mark -

@implementation NSWindow (AnimationFlipWindow)

+ (NSWindow *) initForAnimation:(NSRect)aFrame {

    NSWindow *window =  [[NSWindow alloc] initWithContentRect:aFrame 
                                                    styleMask:NSBorderlessWindowMask 
                                                      backing:NSBackingStoreBuffered 
                                                        defer:NO];
    [window setOpaque:NO];
    [window setHasShadow:NO];
    [window setBackgroundColor:[NSColor clearColor]];
    [window.contentView setWantsLayer:YES];

    return window;
}

@end

#pragma mark -

@implementation NSView (AnimationFlipWindow)

- (CALayer *) layerFromWindow {

    NSBitmapImageRep *image = [self bitmapImageRepForCachingDisplayInRect:self.bounds];
    [self cacheDisplayInRect:self.bounds toBitmapImageRep:image];

    CALayer *layer = [CALayer layer];
    layer.contents = (id)image.CGImage;
    layer.doubleSided = NO;

    // Shadow settings based upon Mac OS X 10.6
    [layer setShadowOpacity:0.5f];
    [layer setShadowOffset:CGSizeMake(0,-10)];
    [layer setShadowRadius:15.0f];


    return layer;
}

@end

The header file:

@interface AnimationFlipWindow : NSObject {

    BOOL _flipForward;

    NSWindow *mAnimationWindow;
    NSWindow *mTargetWindow;
}

// Direction of flip animation (property)
@property (readwrite, getter=isFlipForward) BOOL flipForward;

- (void) flip:(NSWindow *)activeWindow 
       toBack:(NSWindow *)targetWindow;
@end

#pragma mark -
#pragma mark CategoryMethods:

@interface CAAnimation (AnimationFlipWindow)
+ (CAAnimation *) animationWithDuration:(CGFloat)time 
                                   flip:(BOOL)bFlip // Flip for each side
                                forward:(BOOL)forwardFlip; // Direction of flip
@end

@interface NSWindow (AnimationFlipWindow)
+ (NSWindow *) initForAnimation:(NSRect)aFrame;
@end

@interface NSView (AnimationFlipWindow)
- (CALayer *) layerFromWindow;
@end

EDIT: This will animate to flip from one window to another window. You can apply the same principals to a view.

Answer 4

Mike Lee has an implementation of the flip effect for which he has released some sample code. (Unfortunately, this is no longer available online, but Drew McCormack built off of that in his own implementation.) It appears that he grabs the layers for the "background" and "foreground" views to be swapped, uses a CATransform3D to rotate the two views in the animation, and then swaps the views once the animation has completed.

By using the layers from the views, you avoid needing to cache into a bitmap, since that's what the layers are doing anyways. In any case, his view controller looks to be a good drop-in solution for what you want.

Answer 5

There's a complete open source implementation of this by the guys at Mizage.

You can check it out here: https://github.com/mizage/Flip-Animation

Answer 6

Probably not the case in 2008 when this question was asked, but this is pretty easy these days:

[UIView animateWithDuration:0.5 animations:^{
    [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:self.iconView cache:YES];
    /* changes to the view made here will be reflected on the flipped to side */
}];

Note: Apparently, this only works on iOS.