Mac OS X Leopard - ARCAism

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CHAPTER 24 MAC OS X DEVELOPMENT: THE APPLICATION FRAMEWORKS
Beauty
NOTE For more on Safari, see Chapter 10. For more on Dashboard, see Chapter 3.
As a platform, the Mac has always been known as the place to be for graphics. Whether or not
that’s true, Mac OS X and its Aqua interface are certainly gorgeous. Applications on the Mac
inherit the system’s aesthetic brilliance for free, whether they are written in modern Cocoa, oldfashioned
Carbon, or even a guest platform like Java.
That’s because the application frameworks let developers build applications without worrying
about any but the highest-level details of the graphics system. Little do they know that far
below, OpenGL sits waiting for anyone who would dare traverse its sharp learning curve in the
quest for pureness of power, flexibility, and performance.
Luckily, between these two extremes lies Quartz, the graphics compositing engine. Quartz
can be accessed via a series of graphics frameworks that provide expressiveness with images,
animation, video, and drawing, while still maintaining a good dose of abstraction from the nittygritty
details of OpenGL routines and primitives.
When the free graphics from the application frameworks leave you feeling like you’ve gotten
what you’ve paid for, it’s time to peek beneath the shiny skin of your Apple and examine the
power that lies at its core.
Core Animation
If a computer interface is more like the real world, it’s more familiar, and therefore more usable.
But computers are, in many ways, inherently alien to our everyday experiences. Contrast the
instant on-off state change of a transistor to the slow opening and closing of a door.
The obvious solution is to smooth the transitions between state changes using animation.
While simple in theory, the difficulty in implementing animation has long forced developers to
compromise between the ideals of user interface and the realities of a deadline.
Leopard’s new Core Animation framework frees developers from this drudgery and introduces
a lightweight layer-based design metaphor. By enabling and encouraging experimentation,
Core Animation may well make Leopard the biggest revolution in human interface design since
1984.
Layers encapsulate drawing properties like color, border, opacity, and a completely customizable
shadow. They also contain geometric properties like size and position, and the full
range of affine transformations. Layers can contain images, stacks of Core Image filters (which
we’ll get to in a moment), and an alpha mask. They can also be stacked and nested.
What really sets a layer apart is what happens when you change a property. Rather than just
reflecting the new state, the layer animates the transition. Multiple properties can be changed at
the same time. For example, a layer could simultaneously shrink, slide, rotate, and fade.
These animations are optimized to take advantage of hardware acceleration and other video
card niceties, as well as being automatically threaded. Not only will the animation not block
your main thread, but you can change a property while it is in the process of changing, and it will
immediately be rerouted.
The animation itself is also encapsulated as an object, so aside from being adjustable in the
usual ways, such as duration, animations can be subclassed to provide for things like keyframes
or following a Bézier path.
As if all that weren’t enough, you can take advantage of Core Animation without even writing
code. Views can be layer-backed, and many layer properties are accessible from within
Interface Builder, as shown in Figure 24-16.