Question

I’m attempting to implement window-flipping identical to that in iWork –

https://dl.dropbox.com/u/2338382/Window%20Flipping.mov

However, I can’t quite seem to find a straightforward way of doing this. Some tutorials suggest sticking snapshot-images of both sides of the window in a bigger, transparent window and animate those. This might work, but seems a bit hacky, and the sample code is always bloated. Some tutorials suggest using private APIs, and since this app may be MAS-bound, I’d like to avoid that.

How should I go about implementing this? Does anyone have any hints?

NSWindow+Flipping

I’ve rewritten the ancient code linked below into NSWindow+Flipping. You can grab these source files from my misc. Cocoa collection on GitHub, PCSnippets.

Answer 1

You can achieve this using CoreGraphics framework. Take a look at this:

- (void) flipWithDuration: (float) duration forwards: (BOOL) forwards
{
  CGSTransitionSpec spec;
  CGSTransitionHandle transitionHandle;
  CGSConnection cid = CGSDefaultConnection;

  spec.type = CGSFlip;
  spec.option = 0x80 | (forwards ? 2 : 1);
  spec.wid = [self windowNumber];
  spec.backColor = nil;

  transitionHandle = -1;
  CGSNewTransition (cid, &spec, &transitionHandle);
  CGSInvokeTransition (cid, transitionHandle, duration);
  [[NSRunLoop currentRunLoop] runUntilDate: 
        [NSDate dateWithTimeIntervalSinceNow: duration]];
  CGSReleaseTransition (cid, transitionHandle);
}

You can download sample project: here. More info here.

UPDATE:

Take a look at this project. It’s actually what You need.

About this project:

This category on NSWindow allows you to switch one window for
another, using the “flip” animation popularized by Dashboard widgets.
This was a nice excuse to learn something about CoreImage and how to
use it in Cocoa. The demo app shows how to use it. Scroll to the end
to see what’s new in this version!

Basically, all you need to do is something like:

[someWindow flipToShowWindow:someOtherWindow forward:YES];

However, this code makes some assumptions: — someWindow (the initial
window) is already visible on-screen. — someOtherWindow (the final
window) is not already visible on-screen. — Both windows can be
resized to the same size, and aren’t too large or complicated — the
latter conditions being less important the faster your CPU/video card
is. — The windows won’t go away while the animation is running. — The
user won’t try to click on the animated window or do something while
the animation is running.

The implementation is quite straightforward. I move the final to the
same position and size as the initial window. I then position a larger
transparent window so it covers that frame. I render both window
contents into CIImages, hide both windows, and start the animation.
Each frame of the animation renders a perspective-distorted image into
the transparent window. When the animation is done, I show the final
window. Some tricks are used to make this faster; the flipping window
is setup only once; the final window is hidden by setting its alpha to
0.0, not by ordering it out and later ordering it back in again, for instance.

The main bottleneck is the CoreImage filter, and the first frame
always takes much longer to render — 4 or 6 times what it takes for
the remaining frames. I suppose this time is spent with setup and
downloading to the video card. So I calculate the time this takes and
draw a second frame at a stage where the rotation begins to show. The
animation begins at this point, but, if those first two frames took
too long, I stretch the duration to make sure that at least 5 more
frames will get rendered. This will happen with slow hardware or large
windows. At the end, I don’t render the last frame at all and swap the
final window in instead.