Cg编程指南：实时图形编程的终极教程

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"The Cg Tutorial: The Definitive Guide to Programmable Real-Time Graphics" 《The Cg Tutorial》是一本详细指南，专注于可编程实时图形的Cg编程语言。这本书在线上可购，并提供由InformIT和Addison-Wesley提供的30%折扣。作者在书中的"Recent Documents"页面分享了最新的白皮书和会议演示文稿，以帮助读者解决项目中的问题。第1章：介绍本章分为四个部分： 1.1 "什么是Cg？" 这一部分介绍了Cg编程语言。Cg语言允许你控制使用可编程图形硬件绘制的对象的形状、外观和运动。它将这些属性的程序化控制与高性能图形处理相结合。 1.2 "顶点、片段和图形流水线" 解释了现代图形硬件的数据流，并说明了Cg如何融入这个数据流。在图形渲染过程中，顶点经过一系列处理步骤，最终转化为屏幕上的像素，即片段。Cg语言可以在这个过程中用于定制这些处理步骤，实现复杂的视觉效果。 1.3 "Cg的历史发展" 回顾了Cg语言的发展历程，这有助于理解其设计理念和目标，以及它是如何适应图形技术演进的。 1.4 "Cg环境" 描述了应用程序如何通过Cg运行时系统和现有的3D应用编程接口（APIs）来使用Cg程序。这包括如何集成Cg到不同的图形库，如OpenGL或Direct3D，以实现跨平台的图形编程。 Cg的核心特性在于它的灵活性和效率。它提供了一种高级的、面向对象的语言，用于编写顶点着色器和片段着色器，这些是图形管道中的关键组件。顶点着色器处理模型的几何信息，而片段着色器则决定像素的颜色和透明度。通过Cg，开发者可以创建复杂的光照模型、纹理映射、动画效果和高级的物理模拟。此外，Cg还支持动态编译，这意味着在运行时可以创建和修改着色器代码，以适应游戏或应用中的不同场景。这使得开发者能够在不影响性能的前提下，实现高度动态和交互式的图形效果。学习Cg教程不仅对游戏开发者有益，也适用于电影特效、虚拟现实、科学可视化等领域。通过深入理解和熟练运用Cg，开发者能够充分利用现代GPU的计算能力，创造出令人惊叹的实时图形体验。

and Windows PCs, OpenGL is supported by Apple for its Macintosh personal computers. Linux users can use

either the Mesa open-source implementation of OpenGL or a hardware-accelerated implementation such as

NVIDIA's OpenGL driver for Linux. This flexibility makes OpenGL the industry's best cross-platform

programming interface for 3D graphics.

Over the last decade, OpenGL has evolved along with graphics hardware. OpenGL is extensible, meaning that

OpenGL implementers can add new functionality to OpenGL in an incremental way. Today, scores of OpenGL

extensions provide access to all the latest GPU features. This includes ARB-standardized extensions for vertex

and fragment programmability. As extensions are established, they are often rolled into the core OpenGL

standard so that the standard as a whole advances. At the time of this writing, the current version of OpenGL

is 1.4. Ongoing work to evolve OpenGL is underway in various OpenGL ARB working groups. This work

includes both assembly-level and high-level programmable interfaces. Because Cg operates as a layer above

such interfaces, it will continue to function with future revisions of OpenGL in a compatible manner.

Direct3D

Microsoft began developing the Direct3D programming interface about 1995 as part of its DirectX multimedia

initiative. Direct3D is one of the programming interfaces that make up DirectX. Microsoft introduced DirectX

and Direct3D to jump-start the consumer market for 3D graphics, particularly gaming, on Windows PCs.

Microsoft's Xbox game console also supports Direct3D. Direct3D is the most popular graphics API for games

on Windows, due to its history of closely matching the capabilities of available graphics hardware.

Every year or so, Microsoft has updated DirectX, including Direct3D, to keep up with the rapid pace of PC

hardware innovation. The current version of DirectX at the time of this writing is DirectX 9, which includes

HLSL, Microsoft's implementation of the same language syntax and constructs found in Cg.

3D Programming Interface D ente

A few years ago, OpenGL and Direct3D competed to see which programming interface would dominate,

particularly in the domain of Windows PCs. The competition continues to be good for both programming

interfaces, and each has improved in performance, quality, and functionality. In the area of GPU

programmability that Cg addresses, both programming interfaces have comparable capabilities. This is

because both OpenGL and Direct3D run on the same GPU hardware and the graphics hardware determines

the available functionality and performance. OpenGL has a slight advantage in functionality because hardware

vendors are better able to expose their entire feature set through OpenGL, though vendor-specific extensions

do add some complexity for developers.

Most software developers now choose a 3D programming interface based on programmer preference,

history, and their target market and hardware platform, rather than on technical grounds.

Cg supports either programming interface. You can write C g programs so that they work with either the

OpenGL or Direct3D programming interface. This is a huge boon for 3D content developers. They can pair

their 3D content with programs written in Cg and then render the content no matter what programming

interface the final application uses for 3D rendering.

1.4.2 The Cg Compiler and Runtime

No GPU can execute Cg programs directly from their textual form. A process known as compilation must

translate Cg programs into a form that the GPU can execute. The Cg compiler first translates your C g

program into a form accepted by the application's choice of 3D programming interface, either OpenGL or

Direct3D. Then your application transfers the OpenGL or Direct3D translation of your Cg program to the GPU

using the appropriate OpenGL or Direct3D commands. The OpenGL or Direct3D driver performs the final

translation into the hardware-executable form your GPU requires.

The details of this translation depend on the combined capabilities of the GPU and 3D programming interface.

How a Cg program compiles its intermediate OpenGL or Direct3D form depends on the type and generation of

GPU in your computer. It may be that your GPU is not capable of supporting a particular valid Cg program

because of limitations of the GPU itself. For example, your Cg fragment program will not compile if your

program accesses more texture units than your target GPU supports.

Support for Dynamic Compilation

When you compile a program with a conventional programming language such as C or C ++, compilation is an

offline process. Your compiler compiles the program into an executable that runs directly on the CPU. Once

compiled, your program does not need to be recompiled, unless you change the program code. We call this

static compilation.

C g is different because it encourages dynamic compilation, although static compilation is also supported. The

Cg compiler is not a separate program but part of a library known as the Cg runtime. 3D applications and

games using Cg programs must link with the C g runtime. Applications using C g then call C g runtime routines,

all prefixed with the letters

, to compile and manipulate Cg programs. Dynamic compilation allows C g

programs to be optimized for the particular model of GPU installed in the user's machine.

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CgGL and CgD3D, the 3D-API-Specific Cg Libraries

In addition to the core Cg runtime, Cg provides two closely related libraries. If your application uses OpenGL,

you will use the CgGL library to invoke the appropriate OpenGL routines to pass your translated Cg program

to the OpenGL driver. Likewise, if your application uses Direct3D, you will use the CgD3D library to invoke

the appropriate Direct3D routines to pass your translated Cg program to the Direct3D driver. Normally, you

would use either the CgGL or the C gD3D library, but not both, because most applications use either OpenGL

or Direct3D, not both.

Compared with the core C g runtime library that contains the C g compiler, the C gGL and C gD3D libraries are

relatively small. Their job is to make the appropriate OpenGL or Direct3D calls for you to configure Cg

programs for execution. These calls transfer a translated Cg program to the appropriate driver that will

further translate the program into a form your GPU can execute. For the most part, the CgGL and CgD3D

libraries have similar routines. The routines in the CgGL library begin with

cgGL

; the routines in the C gD3D

library begin with

cgD3D

How the Cg Runtime Fits into Your Application

Figure 1-13 shows how a typical 3D application uses the Cg libraries. If you are a programmer, you will want

to learn more about the Cg runtime and the specific library for the 3D API your application uses to render 3D

graphics. Most of this book focuses on the Cg language itself and on how to write C g programs, but Appendix

B has more information about the Cg runtime library.

Figure 1-13 How C g Fits into a Standard C g Application

1.4.3 The CgFX Toolkit and File Format

C g programs need 3D models, textures, and other data to operate on. A Cg program without any associated

data is useless. Cg programs and data also require the correct 3D programming interface configuration and

state. It is often helpful to have a way to bundle all the information required to render a 3D model, including

its associated Cg program.

What CgFX Provides

C gFX is a standardized file format for representing complete effects and appearances. As they did with Cg,

Microsoft and NVIDIA collaborated to develop the CgFX format. C gFX files are text-based, with a syntax that

is a superset of Cg's, and may contain any number of C g programs. The

.fx

suffix identifies CgFX files. A

CgFX file describes the complete render state for a particular effect: multiple passes, texture states, and any

number of individual vertex and fragment programs may be defined to create a complete appearance or

effect. An accompanying development toolkit is provided for using and parsing CgFX files. The toolkit exposes

user-interface hooks to host applications, so that CgFX-aware applications can automatically supply

meaningful controls and semantics to users and developers alike.

Cg programs describe the vertex or fragment processing that takes place in a single rendering pass, but

some complex shading algorithms require multiple rendering passes. CgFX offers a format to encode complex

multipass effects, including designating which C g program is used for each rendering pass.

More specifically, CgFX supports three additional capabilities beyond what the core C g language supports:

CgFX provides a mechanism for specifying multiple rendering passes and optional multiple

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implementations for a single effect.

CgFX allows you to specify nonprogrammable rendering states, such as alpha-test modes and

texture-filtering. The settings for these render states may take the form of simple expressions,

which are evaluated on the CPU when the effect is initialized.

CgFX allows annotations to be added to shaders and shader parameters. These annotations provide

additional information to applications, including content creation applications. For example, an

annotation can specify the allowed range of values for a shader parameter.

Multiple Shader Instancing

The CgFX file format encapsulates multiple implementations of C g programs for a given shader. This means

you can have one Cg shader program written for a third-generation or fourth-generation GPU, while also

including a simpler program that supports a less capable, second-generation GPU. An application loading the

CgFX file can determine at runtime the most appropriate shader implementation to use based on the

computer's available GPU.

Multiple instancing of C g programs with CgFX is one way to address the functional variations in GPUs of

different generations or different hardware vendors. Multiple instancing also lets you develop a Cg program

specialized for a particular 3D API—for example, if OpenGL exposes extra functionality through an extension.

Cg programs specialized for Direct3D, standard OpenGL, or OpenGL with extensions can all be contained in a

single CgFX file.

CgFX and Digital Content Creation

The CgFX Toolkit consists of the C gFX compiler, which supports the full C gFX syntax; the C gFX runtime API,

for loading and manipulating CgFX files; and plug-in modules for major digital content creation (DC C )

applications such as Alias|Wavefront's Maya and Discreet's 3ds max. Figure 1-14 shows these applications

making use of CgFX. Softimage|XSI 3.0 provides direct support for C g compilation in its Render Tree.

Figure 1-14 Digital C ontent C reation Applications That Use C g and C gFX

Prior to CgFX, there was no standard way for a DC C application to export 3D content with all the associated

shading knowledge necessary to render the content in real time. Now the major DCC applications use C gFX in

their content creation process and support the CgFX file format. This means that C gFX can significantly

improve the artistic workflow from DCC applications to real-time games and other 3D applications. Using

CgFX, artists can view and tweak C g shaders and associated 3D content to see, from within the DC C tool of

their choice, how their work will appear in a 3D game or application.

How CgFX Fits into Your Application

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Figure 1-15 shows how a CgFX file containing multiple instanced shaders is used by an application in

conjunction with the C g runtime and your choice of rendering API. Most of this book focuses on the Cg

language itself and on how to write Cg programs, rather than CgFX, but see Appendix C for more information

about the CgFX file format and its associated runtime API.

Figure 1-15 How C gFX Fits into a Standard Application

Onward to the Tutorial

Having finished this introduction to the C g programming language, you are now ready to take on the tutorial

chapters, which will teach you how to write Cg programs.

1.5 Exercises

The exercises at the end of each chapter help you review your knowledge and develop practical programming

skills.

Answer this: Name two standard 3D programming interfaces for which you can compile Cg

programs. What operating systems does each programming interface support?

Answer this: What are the major stages of the graphics pipeline? In what order are the stages

arranged?

Answer this: Where do vertex and fragment programs fit into the pipeline?

Answer this: What is a vertex? What is a fragment? Distinguish a fragment from a pixel.

Try this yourself: We haven't begun writing Cg programs yet (we'll get there soon enough in the

next chapter), so take a break and watch a good feature-length computer graphics animation such

as Monsters, Inc.

1.6 Further Reading

C g builds on a host of concepts in computer language design, computer hardware design, and computer

graphics. Doing justice to all these contributions in the context of this tutorial is not always practical. What we

attempt in the "Further Reading" section at the end of each chapter is to offer you pointers to learn more

about the contributions that underlie the topics in each chapter.

There are plenty of books on C. The C Programming Language, Third Edition (Prentice Hall, 2000), by Brian

Kernighan and Dennis Ritchie, is a classic; the authors invented the C language. C g includes concepts from

both C and C++. There now may actually be more books about C++ than about C . The classic C ++ book is

The C++ Programming Language, Third Edition (Addison-Wesley, 2000), by Bjarne Stroustrup, who invented

the language.

To learn more about the RenderMan Shading Language, read The RenderMan Companion: A Programmer's

Guide to Realistic Computer Graphics (Addison-Wesley, 1989), by Steve Upstill. Pat Hanrahan and Jim Lawson

published a SIGGRAPH paper about RenderMan called "A Language for Shading and Lighting Calculations"

(ACM Press) in 1990.

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Robert Cook's 1984 SIGGRAPH paper titled "Shade Trees" (AC M Press) motivated the development of

RenderMan.

The development of programmable graphics hardware and its associated languages has been an active and

fruitful research area for almost a decade. Anselmo Lastra, Steven Molnar, Marc Olano, and Yulan Wang at

UNC published an early research paper in 1995 titled "Real-Time Programmable Shading" (AC M Press).

Researchers at UNC also published several papers about their programmable PixelFlow graphics architecture.

Marc Olano and Anselmo Lastra published a SIGGRAPH paper titled "A Shading Language on Graphics

Hardware: The PixelFlow Shading System" (ACM Press) in 1998.

Kekoa Proudfoot, Bill Mark, Svetoslav Tzvetkov, and Pat Hanrahan published a SIGGRAPH paper in 2001

titled "A Real-Time Procedural Shading System for Programmable Graphics Hardware" (ACM Press) that

describes a GPU-oriented shading language developed at Stanford.

Real-Time Rendering, Second Edition (A. K. Peters, 2002), written by Eric Haines and Tomas Akenine-M?ller,

is an excellent resource for further information about graphics hardware and interactive techniques.

The OpenGL Graphics System: A Specification documents the OpenGL 3D programming interface. The best

tutorial for learning OpenGL programming is the OpenGL Programming Guide: The Official Guide to Learning

OpenGL, Third Edition (Addison-Wesley, 1999), by Mason Woo, Jackie Neider, Tom Davis, and Dave Shreiner.

The www.opengl.org Web site serves up much more information about OpenGL.

Documentation for the Direct3D programming interface is available from Microsoft's msdn.microsoft.com

Web site.

NVIDIA provides further information about the Cg runtime, C gFX, and C g itself on its Developer Web site at

developer.nvidia.com/Cg .

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Cg编程指南：实时图形编程的终极教程

[PDF]The.Cg.Tutorial.The.Definitive.Guide.to.Programmable.Real-Time.Graphics.pdf

The.Cg.Tutorial.The.Definitive.Guide.to.Programmable.Real-Time.Graphics.djvu

Cg教程：可编程实时图形的权威指南The Cg Tutorial: The Definitive Guide to Programmable Real-Time Graphics

The Cg Tutorial

Cg教程：实时图形编程的权威指南

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