Zoom-Transition between NSViews

For Briefly, I needed a nice, subtle animation for switching between the detail soundtrack view and the reorderable list view. In OS X Yosemite 10.10.3’s Photos.app, I noticed something I liked very much.
When going into an album, for example, the current view is zoomed out of focus and the new view is zoomed in.

Zoomtransition Animation Gif

NSView+ESSViewCategory

I wrote a little category on NSView to do just that, it’s a one liner (ironically, in this pic, it’s more than one line) :

Line of code

It’s pretty self-explanatory. You pass in the view you want to transition from and the one you want to transition to, the type of transition (zooming in or out), the duration and an optional completionHandler that’s called when the animation ends.

Alternatively, it’s also available as an instance method where the view you call this on will be passed into the class method as fromView:

Instancemethod

The Views

For the transition to work, fromView has to be in a view hierarchy, toView shouldn’t. They should be the same size, otherwise more work on your part is necessary (which I had to do in Briefly because the NSPopover the views reside in resizes before / after the transition), but either way the code provided should give you a nice head start.

fromView’s superview is temporarily set to have a CALayer to make use of Core Animation during the transition. After the animation ends, the superview’s wantsLayer – state is reset to what it was before the animation. If we didn’t do this, the animation would appear sluggish.

ESSViewZoomTransition

As you can see in the gif above, there are two types of the transition:

ESSViewZoomTransitionZoomOut – the transition from the textView to the view with the checkboxes.
ESSViewZoomTransitionZoomIn the transition from the checkbox-view to the textView

How To Use NSView+ESSViewCategory

You’ll have to first add the NSView+ESSViewCategory.h and *.m files to your project.
Please note that the category imports <Quartz/Quartz.h> for Core Animation’s CAMediaTiming class, so you might have to add that framework to your project, too.

fromView
It has to be inside of a view hierarchy. Fades out during the transition.

toView
Can be in a different xib file (for example, a NSViewController) or in the same as fromView. It’s important that it is not already on screen somewhere. Fades in during the transition.

Once you have set up your views, either call the class method and pass fromView and toView as well as the other parameters or call the instance method on fromView.

How It Works

The method creates an NSImage of both toView and fromView, puts them into two NSImageViews that have the same frame as the views and animates those two NSImageViews accordingly (calling imageView.animator.frame = …; and imageView.animator.alphaValue = …; )
Because fromView’s superview temporarily gets a CALayer, .animator is powered by Core Animation, which makes for a much smoother animation than doing the same without a layer-backed view.

ImagecreationCreating an NSImage of toView.

So the views themselves aren’t actually resized, they’re just screenshotted, removed from view as we place the NSImageView on top of it, creating the illusion that nothing happened. Then we animate the NSImageViews and insert toView after the animation is done, removing both NSImageViews.

The Source Code

The repository (a sample OS X app) is available on Github.

It was developed (and tested) on OS X Yosemite 10.10.3 using Xcode 6.3.1, but should work on earlier versions of the operating system.

I have some more source code available here (or directly on my github profile page) if you’re interested. If you have any questions or feedback regarding my open source projects, please be sure to mail or tweet me – I’m looking forward to your feedback!

Enjoy!

Making ZEN (Part 2)

First Concept of ZENFirst concept of ZEN

After last week’s guest blog post by my cousin Sebastian about how he came up with the idea of the iOS game ZEN, the design and conception process behind it and the soundtrack, today it’s my turn to talk about putting it in code and making it all come to life.

The Premise

Like a lot of developers I know, I became intrigued with programming because of games. As a kid, I always wanted to develop games for a living, make the next Diablo. So of course I jumped at the idea of creating a game when my cousin asked me if I was interested.

I had never actually programmed a game before, so when Sebastian approached me about developing a game with him, I was already seeing myself having to learn OpenGL and everything that comes with it.

Luckily, it soon became clear that it would be a 2D game, almost 8-bit-ish, like an old Super Mario Bros game. So my fears of having to learn something new* were put to rest and the more he told me about the game, the more I realized that Core Animation would be the perfect fit for this project.

The game is about a cube with random numbers on it. Your goal is to reach ten with these numbers by turning the cube and selecting the appropriate sides within ten seconds.

ZEN Cube Animation

*just kidding, I love learning new stuff, but for a side-project having to learn OpenGL would have been a little much, especially with all my other apps that need constant attention

Core Animation actually was pretty much made for this kind of stuff. Even if the game had had some 3D effects (for example, some sort of perspective distortion when turning the cube, etc), it would have been fairly easy to implement.

First Blood

The first thing I did in the process of developing ZEN was to prototype the cube itself. I began by mapping out the cube because a) I didn’t have one handy and b) to get a visual on each side:

Mapping out the cube

Because I was using Core Animation and it was all in 2D space, I had to figure out what side would go where when the cube was turned from left to right, right to left, from the top or the bottom, so that the numbers would stay on the same side and not end up any place they shouldn’t be. I went so far to write down which side would go where once the cube was turned in any direction

Mapping out which cube side would go whereWhich side goes where when turning the cube?

To make the animation possible, I would have to use at least two CALayers that changed in shape and color, and would have to be kept up to date in terms of data (which side holds which number).

One layer would always be hidden, the layer to turn to, so to speak, the other layer would always be visible. They would alternate in doing that.
For example:

Layer 1 is visible with the front number of the cube.
You turn the cube right and layer 2 (still hidden) gets the number of the left side of the cube.
Layer 1 is animated to fold to the right
Layer 2 shows and animates to the full size of the front cube side.
Layer 1 is hidden

Turning Cube Down on PaperTurning the cube from the top on paper

With that done, I had the cube – of course, there were some kinks to be worked out (for example, sometimes the hidden layer would suddenly be visible with a completely wrong size), but basically, the cube was working.
In code, turning the cube upwards looks like this:

- (void)turnUp
{
ESSCubeSide *oldUp = self.topSide;
ESSCubeSide *oldFront = self.frontSide;
ESSCubeSide *oldDown = self.bottomSide;
ESSCubeSide *oldBack = self.backSide;
self._cubeDict[ESSCUBE_FRONT] = oldDown;
self._cubeDict[ESSCUBE_TOP] = oldFront;
self._cubeDict[ESSCUBE_BACK] = oldUp;
self._cubeDict[ESSCUBE_BOTTOM] = oldBack;
}

This is only the data model, of course. The view code just the two layers – resizing them in unison, hiding one layer and showing the other, etc.

Random Numbers

The next thing that had to be done was to fill the cube with random numbers, some of which would add up to ten.

I chose to do the following:

  1. Decide how many sides it takes to solve the current cube (a number between 2 and 6); let’s say it’s 3 – 3 sides to solve the cube.
  2. Loop while we create 3 random numbers between 1 and 9 that add up to ten.
  3. Fill the rest of the cube (3 more sides) with random numbers between 1 and 9.
  4. Shuffle the resulting array of six numbers so the solving sides aren’t always on the same sides
The same principle works for the minus mode, where there are positive and negative integers that you need to select to add up to ten.

Interface

The first interface concept, as you can see in the first screenshot of this blog post, was pretty simple. The title and three buttons. There was no mention of animations!

As it always happens, things change during the development process, you iterate on everything, and the interface gets overhauled as well. This new one was, in my opinion, much nicer as it demonstrates the “cube-y” nature of the game very nicely.

ZEN Line animation

But it took me some time to get there. I was hoping that Sebastian could define the animations in svg or gif or something like that and I could just load them in and display them.
However, I could not do that – apparently iOS doesn’t support svgs or gifs out of the box (and I didn’t want to rely on 3rd party libraries to do the job). After googling around for a couple of days (because, you know, you want to be thorough), I tried doing it in a web view, because these animations would work in the browser. However, I wouldn’t have that amount of control over them as I did with the final approach I took – code it in Core Animation as well.

So I have one view class that, depending on the width and height of the bounds of the view either expands horizontally or vertically. That was the easy part.

The hard part was creating all the views in Xcode’s Interface Builder with the proper dimensions and positioning them so they would define the buttons and letters. I’m just glad the Help – view is not animated 😉 :

Help ViewThe Help View – thankfully for me, not animated

Creating ZEN was a very exciting experience and I learned a lot during the process. As I usually work alone, working within a team on this project (even if it’s just two people) was a breath of fresh air and is a lot of fun, bouncing ideas off of each other, inspiring each other – there’s a whole lot of energy there.
While I do have a few dear friends with whom I can exchange ideas over the internet for my own projects, it’s quite different when you’re one on one, face to face.

It’s been  a lot of fun.

—-
My name is Matt, I’m the developer of Eternal Storms Software. If you’d like to comment, you can catch me on twitter here: [twitter-follow screen_name=’eternalstorms’ show_count=’yes’] or by eMail.