iOS图像与动画处理实战PDF指南

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"iOS的图像和动画处理--pdf版"是一本由Vandad Nahavandipoor编写的关于iPhone和iOS平台图形与动画设计的专业指南。这本书是针对iOS开发者的实用教程，旨在深入探讨如何在苹果的移动操作系统中高效地创建视觉效果和交互体验。该书涵盖了广泛的主题，包括但不限于： 1. 图像处理基础：介绍iOS设备的显示特性、色彩管理、图像格式和优化，以及如何使用Core Graphics API进行自定义绘图和图像操作。 2. 图形编程：讲解如何利用UIKit、Core Animation和SpriteKit等框架，创建复杂的用户界面元素，实现平滑的动画效果，以及进行2D和3D图形渲染。 3. 动画设计原理：作者详细阐述了关键帧动画、弹簧物理模拟、手势识别和过渡效果的设计方法，帮助读者掌握动态界面设计的最佳实践。 4. 触摸反馈与交互：书中讨论了如何通过触控反馈增强用户体验，如何设计吸引人的触摸手势，以及响应式动画的实现策略。 5. 性能优化：针对iOS设备的资源限制，作者分享了优化图形和动画性能的技巧，如使用CABasicAnimation和CALayer的高效编程方法，以及避免过度渲染的建议。 6. 实战项目与案例分析：书中包含多个实际项目示例，让读者通过实践学习，更好地理解和应用所学知识。版权信息表明，这是一本享有版权的作品，可供教育、商业或销售推广用途。O'Reilly Media提供了在线版本供读者访问，并提供了联系方式以便获取更多关于版权和购买的信息。 "iOS的图像和动画处理--pdf版"是一本不可或缺的参考书籍，无论你是iOS开发者还是UI/UX设计师，都可以从中获得宝贵的知识和实践经验，提升你的iOS应用程序的视觉吸引力和用户体验。

Graphics and Animations

You’ve certainly seen applications with beautiful graphics effects on iPhones or iPads.

And you’ve probably also encountered impressive animations in games and other apps.

When the iOS runtime and Cocoa programming frameworks combine, they make an

amazing variety of graphics and animation effects possible with relatively simple cod-

ing. The quality of these graphics and animations depends partly, of course, on the

aesthetic sensitivities of the programmer and artistic collaborators. But in this short

book, you’ll see how much you can accomplish with modest programming skills.

I’ll dispense with conceptual background, preferring to introduce ideas such as color

spaces, transformation, and the graphics context as we go along. I’ll just mention a few

basics before leaping into code.

In Cocoa Touch, an app is made up of windows and views. An app with a UI has at

least one window that contains, in turn, one or more views. In Cocoa Touch, a window

is an instance of UIWindow. Usually, an app will open to the main window and the

programmer will then add views to the window to represent different parts of the UI:

parts such as buttons, labels, images, and custom controls. All these UI-related com-

ponents are handled and drawn by UIKit.

Some of these things might sound relatively difficult to understand, but I promise you

that as we proceed through this book, you will understand them step-by-step with the

many examples I will give.

Apple has provided developers with powerful frameworks that handle graphics and

animations in iOS and OS X. Some of these frameworks and technologies are:

UIKit

The high-level framework that allows developers to create views, windows, but-

tons, and other UI related components. It also incorporates some of the low-level

APIs into an easier-to-use high-level API.

Quartz 2D

The main engine running under the hood to facilitate drawing in iOS; UIKit uses

Quartz.

Core Graphics

A framework that supports the graphics context (more on this later), loading im-

ages, drawing images, and so on.

Core Animation

A framework that, as its name implies, facilitates animations in iOS.

Basic Concepts for Adapting to Different Screen Sizes

When drawing on a screen, one of the most important concepts to grasp is the relation

between points and pixels. I’m sure you’re familiar with pixels, but what are points?

They’re the device-independent counterpart of pixels. For instance, compare the

iPhone 3GS to the iPhone 4. Both devices have 3.5-inch displays. However, the number

of pixels that iPhone 3GS can draw in portrait mode is 320×480. The same screen size

on the iPhone 4 is capable of drawing twice as many, or 640×960, pixels in portrait

mode.

Now imagine you are writing an iPhone app that has only one screen, and that you are

simply filling the whole screen with the color green. Imagine that you naïvely specify a

rectangular area of 320×480 pixels. When iPhone 3GS users run your app, they will be

quite happy because “it does what it says it does”—fill the entire screen with the color

green. iPhone 4 users, on the other hand, will be quite unhappy: what they will see is

quite different, as shown in Figure 1.

To remedy this problem, Apple introduced device-independent drawing methods to

help developers focus on how their shapes and graphics have to appear on a device

instead of worrying about the screen sizes and resolutions of different devices that run

the same code. To fix the issue we saw in Figure 1, the developer of the app can simply

use the relevant APIs to specify the green rectangle in points instead of pixels. That will

allow the same code to run on the iPhone 3GS and the iPhone 4, ensuring that the

screen on the iPhone 4 will be filled with the rectangle. For this reason, many of the

methods that you will see in this book will rely on points (or as Apple calls them, logical

points) instead of pixels.

The origin point of the screen on an iOS device is the top-left corner.

Screens whose drawing origin is on the top-left corner are also referred

to as Upper Left Origin, or ULO, screens. This means that point (0, 0)

is the topmost and the leftmost point on the screen, and that positive

values of the x axis extend towards the right, while positive values of

the y axis extend towards the bottom. In other words, an x position of

20 is further right on the screen than a position of 10 is. On the y axis,

point 20 is further down than point 10.

2 | Graphics and Animations

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