WebGL编程指南：实战教程

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"Webgl Up and Running - 一本由Tony Parisi编写的关于WebGL的编程教程，涵盖了详细的示例和代码，内容非常新颖。" 在Web开发领域，WebGL（Web Graphics Library）是一种用于在任何兼容的Web浏览器中实现3D图形的JavaScript API。它基于OpenGL ES 2.0规范，通过JavaScript与HTML5 Canvas元素结合，允许开发者无需插件即可在网页上创建交互式的三维图形。"WebGL: Up and Running" 是Tony Parisi撰写的一本面向初学者和进阶者的指南，旨在帮助读者快速掌握WebGL的核心概念和技术。这本书主要围绕以下几个核心知识点展开： 1. **基础概念**：书中首先介绍了WebGL的基本原理，包括向量、矩阵、颜色空间等图形学基础知识。这些概念是理解和编写WebGL代码的基础。 2. **设置环境**：讲解如何在HTML文件中嵌入Canvas元素，并配置WebGL上下文，为后续的3D渲染准备舞台。 3. **图元和绘制**：WebGL支持点、线和三角形等基本图元，书中的例子会演示如何使用这些图元构建复杂的3D模型。 4. **着色器语言GLSL**：WebGL使用GLSL（OpenGL Shading Language）编写顶点和片段着色器，控制图形的渲染效果。书中会深入讲解GLSL语法和常见技巧。 5. **变换与投影**：涵盖物体的平移、旋转和缩放，以及视口变换和投影，这些都是3D场景中不可或缺的部分。 6. **光照与材质**：讲解如何模拟现实世界的光照效果，以及如何定义物体的材质属性，如颜色、反射和透明度。 7. **纹理映射**：使用图像作为表面纹理，增加3D模型的视觉细节和真实感。 8. **缓冲区与顶点数组**：理解如何有效地存储和管理数据，以及如何使用顶点数组和索引来提高性能。 9. **深度测试与剔除**：了解如何使用WebGL的内置机制进行深度排序和剔除不可见面，以优化渲染效果。 10. **交互性**：通过鼠标和触摸事件，实现用户与3D场景的交互，例如拖动旋转、缩放等。 11. **动画与帧率控制**：学习如何创建动态的3D场景，以及如何合理地管理帧率以确保流畅的用户体验。 12. **性能优化**：探讨如何优化WebGL代码，减少重绘次数，提高页面加载速度，以适应不同的设备和网络环境。 13. **最佳实践与未来趋势**：分享WebGL的开发经验，以及该技术的最新进展和可能的应用方向。通过阅读本书，读者不仅可以掌握WebGL的基本使用方法，还能了解到如何创建复杂的3D应用程序，从而在网页设计、游戏开发、数据可视化等领域大展拳脚。同时，作者提供的详细例子和代码可以帮助读者更好地理解和实践所学知识。无论是对于前端开发者还是图形设计师，"WebGL: Up and Running"都是一本极具价值的学习资料。

to Christell Gause, head of support at TurboSquid, for his diligent efforts in helping me

obtain permission from the many TurboSquid artists whose content is featured here.

Also, I could not have created the examples for this book without additional help

and/or contributed content from data junkie Theo Armour, 3D programming ace Don

Olmstead, and 3D artist Arefin Mohiuddin of Sunglass.io.

WebGL is blessed to have a strong community of developers. I would like to thank the

three.js developers, including guru Ricardo Cabello (“Mr.doob”) and contributors Bra

nislav Ulicny (“AlteredQualia”) and Tim Knip, for their patience with my often-naïve

questions and their overall enthusiasm for the project. I owe an eternal debt of gratitude

to Ken Russell, the WebGL working group chair and WebGL development lead at Goo

gle. Ken has not only built a great product, but he kindly agreed to write the foreword

for this book.

Finally, I would like to thank my friends and family. Mark Pesce, my old VRML partner

in crime, is a veteran author. His commitment to excellence in writing and his passion

for emerging technology have been a constant source of inspiration to me over the years.

Many thanks to my buddy and sometimes-business-partner Scott Foe, who was always

supportive of this book, despite the major distraction it created from our day-to-day

startup. Last but not least, my family provided the moral support, patience, and loving

environment that any author needs to thrive. More than that, they pitched in on the

logistics: my 10-year-old, Lucian, gets props for play-testing most of the examples in the

book, and my wife, Marina, kept me honest with art direction so that my cobbled-

together examples would at least have a consistent look and coherent story.

xiv | Preface

www.it-ebooks.info

WebGL is the new standard for 3D graphics on the Web. With WebGL, developers can

harness the full power of the computer’s graphics rendering hardware using only Java

Script, a web browser, and a standard web technology stack. Before WebGL, developers

had to rely on plug-ins or native applications and ask their users to download and install

custom software in order to deliver a true 3D experience.

WebGL is part of the HTML5 family of technologies. While not in the official specifi

cation, it is shipped with most browsers that support HTML5. Like Web Workers, Web

Sockets, and other technologies outside the official W3C recommendations, WebGL is

an essential component in an emerging suite that is transforming the modern browser

into a first-class application platform.

WebGL works on the majority of desktops, as well as a growing number of mobile

browsers. There are millions of WebGL-enabled seats already installed, most likely in

cluding the machines you run at home and in your office. WebGL is at the center of a

vibrant and growing ecosystem that is making the web experience more visually rich

and engaging. There are hundreds of sites, applications, and tools being developed, with

applications ranging from games to data visualization, computer-aided design, and

consumer retail.

While the low-level nature of the WebGL API may appear daunting at first, there are

several open source JavaScript toolkits that take the grunt work out of development. I

want to be careful not to oversell this—3D is still hard work—but these tools at least

make it possible for mere mortals with modest web development experience to get into

the WebGL business. So maybe it’s finally time for you to create that hit game you always

wanted to make. Or maybe today is the day when you blow your boss’s mind with a

dazzling intro graphic for your home page.

In this chapter, we will take a quick tour of the low-level underpinnings of WebGL to

give you a foundation. For the majority of the book, we will use a high-level 3D toolkit,

Three.js, which hides many of the messy details. But it is important to know what these

tools are built upon, so let’s start by exploring WebGL’s core concepts and API.

WebGL—A Technical Definition

WebGL is developed and maintained by the Khronos Group, the standards body that

also governs OpenGL, COLLADA, and other specifications you may have heard of. Here

is the official description of WebGL, from the Khronos website:

WebGL is a royalty-free, cross-platform API that brings OpenGL ES 2.0 to the web as a

3D drawing context within HTML, exposed as low-level Document Object Model inter

faces. It uses the OpenGL shading language, GLSL ES, and can be cleanly combined with

other web content that is layered on top or underneath the 3D content. It is ideally suited

for dynamic 3D web applications in the JavaScript programming language, and will be

fully integrated in leading web browsers.

2 | Chapter 1: An Introduction to WebGL

www.it-ebooks.info

This definition comprises several core ideas. Let’s deconstruct them here:

WebGL is an API

WebGL is accessed exclusively through a set of JavaScript programming interfaces;

there are no accompanying tags like there are with HTML. 3D rendering in WebGL

is analogous to 2D drawing using the Canvas element, in that it is all done through

JavaScript API calls. In fact, access to WebGL is provided using the existing Canvas

element and obtaining a special drawing context specific to WebGL.

WebGL is based on OpenGL ES 2.0

OpenGL ES is an adaption of the long-established 3D rendering standard OpenGL.

The “ES” stands for “embedded systems,” meaning that it has been tailored for use

in small computing devices, most notably phones and tablets. OpenGL ES is the

API that powers 3D graphics for the iPhone, the iPad, and Android phones and

tablets. . WebGL’s designers felt that, by basing the API on OpenGL ES’s small foot

print, delivering a consistent, cross-platform, cross-browser 3D API for the Web

would be more achievable.

WebGL combines with other web content

WebGL layers on top of or underneath other page content. The 3D canvas can take

up just a portion of the page, or the whole page. It can reside inside <div> tags that

are z-ordered. This means that you develop your 3D graphics using WebGL, but all

your other elements are built using familiar old HTML. The browser composites

(combines) all of the graphics on the page into a seamless experience for the user.

WebGL is built for dynamic web applications

WebGL has been designed with web delivery in mind. WebGL starts with OpenGL

ES, but it has been adapted with specific features that integrate well with web

browsers, work with the JavaScript language, and are friendly for web delivery.

WebGL is cross-platform

WebGL is capable of running on any operating system, on devices ranging from

phones and tablets to desktop computers.

WebGL is royalty-free

Like all open web specifications, WebGL is free to use. Nobody will be asking you

to pay royalties for the privilege.

The makers of Chrome, Firefox, Safari, and Opera have committed significant resources

to developing and supporting WebGL, and engineers from these teams are also key

members of the working group that develops the specification. The WebGL specification

process is open to all Khronos members, and there are also mailing lists open to the

public. See

Appendix A for mailing list information and other specification resources.

WebGL—A Technical Definition | 3

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“Math is hard!”

—Barbie

3D Graphics—A Primer

As sexist as the infamous quote may be, I have to say that whenever I code something

in 3D, I, like Barbie, get a very strong urge to indulge in shop therapy. It’s hard stuff and

it often involves more than a little math. Luckily, you won’t have to be a math whiz to

build something in WebGL; we are going to use libraries that do most of the hard work

for us. But it is important to understand what’s going on under the hood, and to that

end, here is my attempt to summarize the entire discipline of interactive 3D graphics in

a few pages.

3D Coordinate Systems

3D drawing takes place, not surprisingly, in a 3D coordinate system. Anyone familiar

with 2D Cartesian coordinate systems such as you find on graph paper, or in the window

coordinates of an HTML document, knows about

x and y values. These 2D coordinates

define where <div> tags are located on a page, or where the virtual “pen” or “brush”

draws in the case of the HTML Canvas element. Similarly, 3D drawing takes place in a

3D coordinate system, where there is an additional coordinate,

z, which describes depth

(i.e., how far into or out of the screen an object is drawn). The WebGL coordinate system

is arranged as depicted in Figure 1-2, with x running horizontally left to right, y running

vertically bottom to top, and positive

z coming out of the screen.

If you are already comfortable with the concept of the 2D coordinate system, I think the

transition to a 3D coordinate system is pretty straightforward. However, from here on,

things get a little complicated.

Meshes, Polygons, and Vertices

While there are several ways to draw 3D graphics, by far the most common is to use a

mesh. A mesh is an object composed of one or more polygonal shapes, constructed out

vertices (x, y, z triples) defining coordinate positions in 3D space. The polygons most

typically used in meshes are triangles (groups of three vertices) and quads (groups of

four vertices). 3D meshes are often referred to as

models.

Figure 1-3 illustrates a 3D mesh. The dark lines outline the quads that comprise the

mesh, defining the shape of the face. (You would not see these lines in the final rendered

image; they are included for reference.) The

x, y, and z components of the mesh’s vertices

define the shape only; surface properties of the mesh, such as the color and shading, are

defined using additional attributes, as we will discuss shortly.

4 | Chapter 1: An Introduction to WebGL

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