iCal-like popup window Part I - MAAttachedWindow and CoreAnimation

I have been working on animating the insert frames window in the same way that the iCal window animates. The iCal window does not just appear but instead sort of grows out of the point that you double clicked in.

It is a really nice effect - however rather than the 10 minuets (or so) I thought it would take to deploy it - in actual fact it has taken me a little while to get to the bottom of it.

My first port of call was Core Animation. I have not done any Core Animation before so it was my first look at it. Core Animation is beautiful - doing simple animations is pretty straight forward. An animation like changing a window's bounds or moving it's location is quite simple. However it is not possible to do this kind of animation with Mat Gemmel's MAAttachedWindow.

MAAttachedWindow is quite interesting and clever - what it does is create a pattern that is the window image (a bitmap) and then sets this pattern as the window background colour. So when the window draws it's background in it's background colour this magically draws the window. There is also some code that will keep the window geometry in sync with it's contents this makes it impossible to grow or shrink the window.

I had a solution to this which was to use Core Animation to resize the contents of the window and from this then recalculate the geometry of the window its self. This sort of worked - things animated but in a nasty lumpy fashion. Grubbing around on the web I found this reference to the problem.

The arrow is harder. There's a window with an arrow on Matt Gemmell's site http://mattgemmell.com/ but that uses an NSColor with a pattern image to fill the window background and that seems mess up with core animation, which can't cache the drawn window prior to animation.

There are other ways to draw custom windows. Apple have some excellent Sample code RoundTransparentWindow that draws a custom window. Their method is a little more straight forward than MAAttachedWindow - the window is 100% transparent and within the window is a view that draws the window background. Taking this approach and rolling my selves up for some fun and games with drawing paths gave me a window that animated smoothly.

As you can see - animates nice and smoothly - but is very different than what happens in iCal.