After Effects表达式深度解析：AE进阶指南

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"After Effects Expressions 是一本由 Marcus Geduld 编写的关于 After Effects 表达式的教程，适合 AE 的进阶学习者。该资源为英文版，但内容表述清晰，易于理解。" After Effects（简称AE）是Adobe公司开发的一款强大的视频特效合成软件，广泛应用于电影、电视和网络的后期制作中。表达式是AE中的一个核心功能，它允许用户通过编写简单的代码来控制图层、属性和时间线的行为，极大地提高了工作效率和创意表达。在 "After Effects Expressions" 这本书中，作者 Marcus Geduld 深入浅出地讲解了如何利用表达式来增强动画和视觉效果。这本书涵盖了从基础到高级的各种表达式用法，包括但不限于以下几个方面： 1. **基础表达式语法**：介绍基本的表达式结构，如变量、运算符、函数和控制流语句，帮助读者理解和创建自定义表达式。 2. **属性链接与操控**：讲解如何通过表达式链接不同图层的属性，实现动态关联，以及如何使用 `thisComp` 和 `thisLayer` 对象访问当前合成和图层信息。 3. **时间线控制**：探讨如何使用表达式来操纵时间，如创建缓动效果、循环动画和触发事件。 4. **数学与颜色表达式**：解释如何应用数学函数处理数值，以及如何操作颜色值，包括色彩空间转换和颜色调整。 5. **内置表达式**：介绍AE提供的预设表达式，如 ` Wiggle()` 用于创建随机颤动效果，`loopOut()` 用于循环播放动画等。 6. **脚本与表达式组合**：讨论如何将表达式与After Effects的脚本语言 ExtendScript 结合，进一步提升自动化工作流程的能力。 7. **实例分析与项目实践**：书中包含大量实际案例，通过这些实例，读者可以了解如何将理论知识应用到实际项目中，提高解决实际问题的能力。 8. **优化与性能**：指导如何编写高效的表达式，避免因表达式复杂度过高导致的渲染速度减慢问题。 9. **解决问题与调试**：教授如何识别和修复表达式错误，提高调试技巧。通过这本教程的学习，无论是后期制作的专业人士还是对AE感兴趣的初学者，都能掌握表达式的精髓，提升自己的技能水平，创造出更加生动和富有创意的视觉作品。尽管是英文版，但因其简洁明了的写作风格，即使是英语非母语的读者也能轻松理解和应用。同时，读者还可以通过Elsevier出版社获取版权许可，合法复制或引用书中的内容。

Introduction

or “The dog was taken for a walk by me. ” The latter is awkward, but it still

makes sense. We can understand it. But that’s because we’re smart. Computers

are dumb. They only understand commands that follow rigid rules, so when

we write JavaScript, we need to follow these rules.

That actually makes JavaScript much easier to learn than a human language. If

you learn French or German, you need to expend a lot of energy memorizing

irregular verbs and genders. Because JavaScript is so rigid, there are few irregu-

larities. Wiggle is always wiggle. It’s never wiggled, wiggler, or wobble.

You may have heard of JavaScript before. It’s built into web browsers, such as

Safari, Firefox, and Internet Explorer. It’s also built into Photoshop, Illustrator,

After Effects, Dreamweaver, and many other graphics and design applications.

Flash employs a JavaScript-like language called Actionscript. The Expressions

language is based on a subset of JavaScript, with a bunch of AE-speciﬁ c addi-

tions thrown in by Adobe.

If you’re like many designers I’ve met, you’re probably starting to hyperventi-

late about now. “I didn’t sign aboard to be a programmer! ” you’re thinking.

“ Where’s the exit? ”

I started out as a designer with no interest in programming. But I had to do

some web design, and I needed to learn JavaScript to create some animated

effects. My intention was to learn just a tiny bit of programming: just enough

to achieve the effects I was working on. But as my projects grew in complexity,

I gradually found myself learning more and more. After a while, I understood

JavaScript as well as, say, an American might understand French if he’s lived in

Paris for a few years and has had to use it each day to ask, “How much does

that cost? ” and “Where’s the bathroom? ”

When I got into AE, I was thrilled to discover that it spoke the same lan-

guage as web browsers. If it hadn’t, I might never have learned Expressions. I

really didn’t want to learn a second language. Luckily, I didn’t have to. And

as I leveraged my JavaScript skills within AE Comps, my programming skills

got stronger. Eventually, I learned Flash programming, and once again found

myself speaking JavaScript—this time like a native.

You may have no interest in becoming a computer programmer, but if you learn

some JavaScript, even if you learn it kicking and screaming, you’ll have new tools

that can help you out in many of the applications that you use every day.

Introduction

xvi

AE lets you use JavaScript in two different ways: Expressions and applica-

tion scripting. Expressions let you manipulate effects and transforms in the

Timeline. In other words, they are tools to help you create animation and

compositing effects. Application scripting allows you to control After Effects

itself. With scripting, you can add new commands to AE’s menus. You could,

for instance, add a command that automatically renders out a Comp at 3:30

on Wednesday and e-mails you when it’s done. Such scripting is also avail-

able in Photoshop and Illustrator to help you extend the feature sets of those

applications.

Because this is an Expressions book, that’s all I’m going to say about applica-

tion scripting. But it’s nice to know that, once you learn Expressions, you won’t

have to learn a whole new language for scripting. (If you want to play with

some sample scripts, you can ﬁ nd them in the File  Scripts menu.)

One more note about JavaScript. It’s not the same as Java. Java is a completely

different language (used mostly on web servers and never in AE). Not surpris-

ingly, people always confuse Java and JavaScript with each other. JavaScript

is not a “lite” version of Java. JavaScript is as distinct from Java as Spanish is

from Portuguese. Why do they have such similar names? Because the company

that developed JavaScript (Netscape) had a partnership with the company that

developed Java (Sun Microsystems). Rumor has it that the Sun developers drink

a lot of coffee. Go ﬁ gure.

DO I NEED TO BE A PROGRAMMER?

No. Although you write Expressions in JavaScript, which is a programming

language, you don’t need to be a programmer to craft useful Expressions. You

don’t even need to know much about JavaScript. In fact, the beginning chapters

of this book will show you tons of useful techniques you can use without any

programming knowledge at all. And although it’s true that you can go on to do

even more useful things if you do know how to program, you’re not limited to

boring, 101-type effects if you don’t. You can create complex, original effects

without coding.

In fact, most of the time you won’t even have to type. AE includes an amazing,

magical tool called the Pick Whip, which allows you to create JavaScript with

your mouse. You drag, point, and click; AE writes the code for you. You don’t

even have to understand the code. It just works.

Introduction

xvii

For readers who want a deeper understanding, I’ve included advanced steps in

later chapters. You can decide, in your own time, whether or not you want to

tackle these chapters. It’s my sincere hope that this book will be useful to you,

even if you only read 50% of it. (Of course, I’d be thrilled if you read the whole

thing.) For those of you who do want to learn it all, I promise to hold your

hand through the process and gradually guide you from the simple to the com-

plex, without making any sudden leaps.

Even if you never delve into complex JavaScript yourself, you can still use other

people’s scripts. JavaScript is just text, and text can be copied and pasted. Back

when I ﬁ rst started to use Expressions, I needed to create a pendulum. But I had

no idea how to write such an Expression. Luckily, I was able to ﬁ nd one online.

I read it and was totally bafﬂ ed by it. It looked like a scary mathematical equa-

tion. For a second, I felt panicked. Then I calmed down, selected the text of

the Expression in my browser, copied it to the clipboard, switched over to AE,

and chose Edit  Paste. Voila! My pendulum swung back and forth beautifully.

I had no idea how it worked, but it worked, and that’s what mattered most.

This book is for those of you who don’t care how it works, as long as it works.

It’s also for those of you who do care how it works and want to be able to cus-

tomize it and write other Expressions that are just as complex. This book is for

the auto mechanic. But it’s also for the guy who just wants to drive his car to

work and doesn’t really care what goes on under the hood.

DO I NEED TO BE GOOD AT MATH?

No. Many Expressions don’t use math at all (even though, in the end, they

spit out numbers). If you have to type at all, you’ll type friendly words like

“ wiggle. ” Of the Expressions that do use math, most use simple arithmetic. So

you may have to strain your brain by adding and subtracting, on occasion.

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