Core Animation入门：Mac和iPhone开发的简化动画技术

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"Core Animation Simplified Animation Techniques for Mac and iPhone Development" 本书《Core Animation Simplified Animation Techniques for Mac and iPhone Development》是一本专为苹果平台（Mac 和 iPhone）开发者编写的关于Core Animation技术的经典教程。作者Marcus Zarra和Matt Long深入浅出地介绍了Core Animation的基本概念、动画技巧以及高级应用，帮助读者掌握这一强大的图形渲染和动画框架。 Core Animation是Apple提供的一种低级API，用于创建复杂的2D和3D图形动画效果，它在Mac OS X和iOS操作系统中扮演着核心角色。通过Core Animation，开发者可以创建出流畅、高性能的用户界面，提升应用程序的视觉体验。书中的主要内容包括： 1. **Core Animation基础**：讲解了Core Animation的基本架构，如何设置层（Layer）以及层的属性，包括位置、大小、透明度等。同时，书中还介绍了如何使用关键帧动画（Keyframe Animation）来创建平滑的过渡效果。 2. **简单动画技巧**：涵盖了如何创建基本的移动、缩放和旋转动画，以及如何结合多个动画形成组动画（Grouped Animation），实现更复杂的行为。 3. **样式指南**：提供了关于何时及如何使用不同动画风格的建议，帮助开发者创建出与应用整体风格协调一致的动画效果。 4. **高级主题**：深入讨论了Core Animation的高级特性，如CAConstraint动画、 CALayer的子类化以及自定义渲染。这些内容有助于开发者实现更高级的动画效果，例如视差滚动、3D转换等。 5. **实战案例**：书中可能包含了一些实际项目中的案例，展示了如何将理论知识应用到实际开发中，解决实际问题。 6. **性能优化**：讨论了如何优化Core Animation的性能，避免不必要的计算，确保动画的流畅性，特别是在资源有限的移动设备上。 7. **开发者工具**：介绍使用Xcode的Instruments工具进行动画性能分析和调试的方法，帮助开发者更好地理解和改进他们的动画代码。通过阅读这本书，无论是初学者还是经验丰富的开发者，都能找到有价值的见解和实用技巧，提升在Mac和iPhone平台上开发动画应用的能力。书中提供的实践指导和深度解析，将使这本书成为开发者长期的参考资源，持续适应苹果平台的未来发展。

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IN THIS CHAPTER

. Animation and the Cartesian

Plane

. Your Free Lunch

. What Is a Layer?

. Animation and Layers

. Math? I Was Told There Would

Be No Math

. Core Animation and the

iPhone

. Notes on Sample Projects

CHAPTER 1

What Is Core

Animation?

Core Animation enables you to develop complex anima-

tions for many different types of applications. You can

simply animate your views within a window, or you can

create a thousand sprites represented by layers on the

screen for that next killer game. In this chapter, we intro-

duce you to the basic concepts behind Core Animation.

We take a look at views and layers to ensure you under-

stand what you can do with animation in each. We start

with a discussion about animation and the coordinate

plane and then move on to getting well acquainted with

the Core Animation base class,

CALayer, and its related

protocols.

Animation and the Cartesian

Plane

When you have become familiar with Core Animation and

start using it in your applications, you will see that anima-

tion is easy on both Mac OS X and the iPhone. The fact is,

though, that animation has not always been easy. Prior to

Core Animation, you needed to understand some fairly

complex subjects such as double buffering and more

complicated mathematics such as plane geometry—espe-

cially if you wanted to give your animations any sense of

depth. Core Animation abstracts all of that away. If you

wanted to move a sprite across the screen doing it the old

way, you needed to create an off-screen graphics context,

draw your sprite to that context, swap out that context

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with one currently on the screen, move the sprite position, and then draw to the swapped

out off-screen graphics context. Lather, rinse, repeat.

Although this process isn’t terribly difficult, it can present some challenges to the

developer that Core Animation completely eliminates. The Core Animation way to do

the exact same thing is to create a layer that contains your sprite and simply call

–setPosition. As you learn in chapters to come, the position of a layer is represented by

a single point on the screen. By default, a layer’s position is the center point of the layer

within its parent’s coordinate space. So what does that mean?

Core Animation uses the standard Cartesian coordinate system you remember from geom-

etry and trigonometry. The values for x are on the horizontal axis, and the values for y are

on vertical axis. When naming a point, the x is always the first value, so a value of 25,35

means x = 25 and y = 35. Different from a standard Cartesian coordinate plane, however,

is that you are only ever using the upper-right portion of the plane where the numbers

are all positive. This means that the bottom-left corner of the screen is at point

0,0. The

upper-right portion of the screen then is the width (x) and height (y) depending on the

resolution of the screen you use. On a 15-inch MacBook Pro, this value is

1440,900. For

example, if you created a sprite on a layer and wanted to animate it from coordinate

0,0

on this MacBook Pro, you could set the position of the sprite to 0,0 when it is created

and then call

–setPosition(CGPointMake(1440,900)) and the sprite layer would animate

to the upper-right corner of the screen. Of course, this assumes that the sprite is in a view

that covers the entire screen, as layers cannot display without being backed by a view.

CHAPTER 1 What Is Core Animation?

Differing Coordinate Systems

One thing you should keep in mind when determining where to position your layers on a view

is that the coordinate system might work differently from one system to another. If you have

experience drawing in a coordinate system on other platforms such as Windows, the coordi-

nate system might feel upside down. On Windows, the origin point

0,0 is located at the

upper-left corner of the screen instead of the bottom-left corner.

Fortunately, if you are used to using a coordinate system that works this way, Cocoa views

provide a simple way to help you feel right at home. You can create your own NSView derived

view and override the method called

–isFlipped. In this method, simply return YES (a true

value) and Quartz (the 2D drawing system) assumes you want to draw everything with your

coordinate origin in the upper-left corner.

Interestingly, this coordinate system—with the origin in the upper-left corner—is the default

for drawing behavior in a

UIView on the iPhone, so keep that in mind if you need to duplicate

drawing functionality between OS X and the iPhone. You want to override

NSView and have

–isFlipped return YES for OS X so that you don’t need to rewrite your code for the iPhone.

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Your Free Lunch

They say that there is no such thing as a free lunch, but when it comes to animating

with Core Animation, you don’t just get lunch, you get a drink and desert as well. For

example, all the drawing going on is happening behind the scenes using OpenGL. Yet,

you don’t need to know anything about OpenGL to take advantage of the hardware accel-

eration offered by your video card. This is fully abstracted by Core Animation. If you do

want to get to the more nuts-and-bolts level of OpenGL, though, you can do so by using

the

CAOpenGLLayer on OS X. As of this writing, things aren’t quite as easy on the iPhone

for OpenGL, but they are not too far off. The layers and layer-backed views on the iPhone

also give you great performance benefits.

Another freebie in Core Animation is that all the animation happens on a background

thread. This means that the user interface isn’t blocked when the animation runs. And

you don’t need to be a multithreading

expert to take advantage of it! In fact, if

you’ve never worked with multiple

threads, you won’t notice a thing. Just

set the

animatable property on your

layer or view and watch the action

happen.

What Is a Layer?

The layer, represented by the CALayer class and its derivatives, is the most basic funda-

mental building block you will use for your all your Core Animation-based applications.

All Core Animation layers provide a lightweight layer within a view that enables you to

display visual content. Here is how Apple describes a

CALayer in the API documentation:

CALayer is the model class for layer-tree objects. It encapsulates the position, size,

and transform of a layer, which defines its coordinate system. It also encapsulates

the duration and pacing of a layer and its animations by adopting the

CAMediaTiming protocol, which defines a layer’s time space.

Notice how it says that it is the “model class.” This might be confusing if you are familiar

with the Model-View-Controller (MVC) design pattern, as you might more naturally think

that because Core Animation is of a visual nature, the View part of MVC might make

more sense. Ultimately, it is the

NSView on the OS X side and the UIView on the iPhone

side in which the layer is stored that does the drawing. The

CALayer simply contains the

data (model) that is relevant to all the layer’s attributes such as background color, border

width, position, size, transform, and such.

What Is a Layer?

NOTE

To learn more about how to use Core

Animation in your iPhone apps, see Chapter

13, “Core Animation on the iPhone.”

From p. 7 of Apple’s CALayer Class Reference: http://developer.apple.com/mac/library/

documentation/GraphicsImaging/Reference/CALayer_class/CALayer_class.pdf.

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. CATextLayer

This layer provides a convenient way to display a string in your layer tree. You

specify all the layout information as with any other layer, but you can also specify

the text, font, font size, and foreground color that the layer uses for the text

provided. If you specify an

NSAttributedString, these other fields with be ignored.

This layer is only available on OS X.

CAScrollLayer

This layer enables you to scroll content that is larger than the viewport of the

containing view.

CATiledLayer

This layer enables zooming and panning of content that is larger than the viewport

of the containing view.

CAOpenGLLayer

This layer provides a convenient way to do OpenGL rendering in your application.

We cover this layer is greater depth in Chapter 8, “OpenGL Layer.” This layer is only

available on OS X.

CAEAGLLayer

This layer provides a way to perform OpenGL rendering on the iPhone. This layer is

only available on the iPhone.

QTMovieLayer

This layer enables you to simply play back QuickTime movies in your Core

Animation-based application. Because it is a Core Animation layer, you can add

additional layers to its

sublayers property and composite other visuals on top of a

playing movie. We cover this layer in greater depth in Chapter 7, “QuickTime

Layers.” This layer is only available on OS X.

QTCaptureLayer

This layer takes advantage of a camera connected to your computer for the purpose

of video capture and real-time playback. You can use your iSight camera or a muxed

device such as a DV camera to capture video. The actual capturing is done via other

QuickTime classes available, but the

QTCaptureLayer enables you to see current

frames from your connected camera in real time. We cover this layer in greater

depth in Chapter 7. This layer is only available on OS X.

QCCompositionLayer

This layer enables you to play back a Quartz composition as part of your Core

Animation-based application. It also enables you to control the Quartz composition

using key-value coding. We cover this layer in greater depth in Chapter, 9 “Quartz

Composer Layer.” This layer is only available on OS X.

What Is a Layer?

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