OpenGL4.0着色器实战指南

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"OpenGL4.0着色器语言书籍，包含60多个专注于实践的OpenGL4.0着色器语言使用技巧。" OpenGL4.0着色语言是图形编程中的一个核心部分，它允许程序员直接控制GPU的行为，以实现复杂的3D图形效果。此书《OpenGL4.0 Shading Language Cookbook》由David Wolff撰写，提供了超过60个高度专注且实用的配方，旨在帮助开发者充分利用OpenGL4.0的着色语言（GLSL）。 OpenGL Shading Language（GLSL）是OpenGL应用程序接口（API）的一部分，它是一种专门设计用于在GPU上运行的高级编程语言。GLSL的主要目标是让开发者能够编写顶点着色器、片段着色器、几何着色器等，这些着色器在图形管线的不同阶段运行，执行光照计算、纹理映射、几何变换等任务。书中涵盖的60多个实战食谱可能包括以下内容： 1. **基础概念**：介绍GLSL的基础知识，如变量类型、常量、运算符和控制流结构，以及如何将着色器编译和链接到OpenGL程序中。 2. **顶点着色器**：讲解如何在顶点着色器中进行坐标变换，实现视口转换、投影变换和模型变换。 3. **片段着色器**：讨论如何处理像素颜色，包括纹理采样、混合模式、深度测试和遮罩操作。 4. **光照和阴影**：深入讲解各种光照模型（如Phong模型），以及阴影贴图和阴影体积等阴影技术。 5. **纹理和滤波**：介绍纹理映射的基本原理，以及不同的纹理过滤技术，如线性过滤、MIP映射和各向异性过滤。 6. **向量和矩阵操作**：探讨向量和矩阵的数学运算，以及它们在3D图形中的应用。 7. **几何着色器**：如何在几何着色器中创建复杂的几何形状，如细分表面、粒子系统和实例化。 8. **高级主题**：可能包括GPU计算、多重渲染目标（MRT）、ubo和ssbo（统一缓冲对象和存储缓冲对象）的使用，以及基于物理的渲染（PBR）等。 9. **性能优化**：讲解如何编写高效的着色器代码，避免不必要的计算和内存访问，以及利用并行性。 10. **调试和错误处理**：介绍如何在没有图形调试器的情况下诊断和修复着色器问题。该书的目的是通过一系列逐步的示例，帮助读者从初级到高级掌握OpenGL4.0着色语言的使用，提升图形编程技能。由于出版时间为2011年，可能不包含后来版本OpenGL的最新特性，但其基础概念和技术对于理解现代GPU编程仍然极具价值。尽管如此，读者在学习时应考虑查阅最新的OpenGL文档和资源，以获取最前沿的信息。

Preface

A block of code is set as follows:

#version 400

in vec3 LightIntensity;

layout( location = 0 ) out vec4 FragColor;

void main() {

FragColor = vec4(LightIntensity, 1.0);

}

When we wish to draw your attention to a particular part of a code block, the relevant lines or

items are set in bold:

QGLFormat format;

format.setVersion(4,0);

format.setProfile(QGLFormat::CoreProfile);

QGLWidget *myWidget = new QGLWidget(format);

New terms and important words are shown in bold. Words that you see on the screen, in

menus or dialog boxes for example, appear in the text like this: "The four corners of the quad are

given by: e0 – ext, e0 – n – ext, e1 + ext, and e1 –n + ext as shown in the preceding diagram".

Warnings or important notes appear in a box like this.

Tips and tricks appear like this.

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Getting Started with GLSL 4.0

Introduction

The OpenGL Shading Language (GLSL) Version 4.0 brings unprecedented power and

exibility to programmers interested in creating modern, interactive, graphical programs.

It allows us to harness the power of modern Graphics Processing Units (GPUs) in a

straightforward way by providing a simple yet powerful language and API. Of course, the rst

step towards using the OpenGL Shading Language version 4.0 is to create a program that

utilizes the latest version of the OpenGL API. GLSL programs don't stand on their own, they

must be a part of a larger OpenGL program. In this chapter, I will provide some tips on getting

a basic OpenGL/GLSL program up and running and some techniques for communication

between the OpenGL application and the shader (GLSL) program. There isn't any GLSL

programming in this chapter, but don't worry, we'll jump into GLSL with both feet in Chapter 2.

First, let's start with some background.

The OpenGL Shading Language

The OpenGL Shading Language (GLSL) is now a fundamental and integral part of the OpenGL

API. Going forward, every program written using OpenGL will internally utilize one or several

GLSL programs. These "mini-programs" written in GLSL are often referred to as shader

programs, or simply shaders. A shader program is one that runs on the GPU, and as the

name implies, it (typically) implements the algorithms related to the lighting and shading

effects of a 3-dimensional image. However, shader programs are capable of doing much more

than just implementing a shading algorithm. They are also capable of performing animation,

tessellation, and even generalized computation.

The eld of study dubbed GPGPU (General Purpose Computing on

Graphics Processing Units) is concerned with utilization of GPUs (often

using specialized APIs such as CUDA or OpenCL) to perform general purpose

computations such as uid dynamics, molecular dynamics, cryptography, and

so on.

Shader programs are designed to be executed directly on the GPU and often in parallel. For

example, a fragment shader might be executed once for every pixel, with each execution

running simultaneously on a separate GPU thread. The number of processors on the graphics

card determines how many can be executed at one time. This makes shader programs

incredibly efcient, and provides the programmer with a simple API for implementing highly

parallel computation.

The computing power available in modern graphics cards is impressive. The following table

shows the number of shader processors available for several models in the NVIDIA GeForce

400 series cards (source:

http://en.wikipedia.org/wiki/Comparison_of_Nvidia_

graphics_processing_units

Chapter 1

Model Unied Shader Processors

GeForce GT 430 96

GeForce GTS 450 192

GeForce GTX 480 480

Shader programs are intended to replace parts of the OpenGL architecture referred to as the

xed-function pipeline. The default lighting/shading algorithm was a core part of this xed-

function pipeline. When we, as programmers, wanted to implement more advanced or realistic

effects, we used various tricks to force the xed-function pipeline into being more exible

than it really was. The advent of GLSL helped by providing us with the ability to replace this

"hard-coded" functionality with our own programs written in GLSL, thus giving us a great deal

of additional exibility and power. For more details on the programmable pipeline, see the

introduction to Chapter 2.

In fact, recent (core) versions of OpenGL not only provide this capability, but they require

shader programs as part of every OpenGL program. The old xed-function pipeline has

been deprecated in favor of a new programmable pipeline, a key part of which is the shader

program written in GLSL.

Proles: Core vs. Compatibility

OpenGL version 3.0 introduced a deprecation model, which allowed for the gradual removal

of functions from the OpenGL specication. Functions or features can now be marked as

deprecated, meaning that they are expected to be removed from a future version of OpenGL.

For example, immediate mode rendering using glBegin/glEnd was marked deprecated in

version 3.0 and removed in version 3.1.

In order to maintain backwards compatibility, the concept of compatibility proles was

introduced with OpenGL 3.2. A programmer who is writing code intended for a particular

version of OpenGL (with older features removed) would use the so-called core prole.

Someone who also wanted to maintain compatibility with older functionality could use the

compatibility prole.

It may be somewhat confusing that there is also the concept of a full vs.

forward compatible context, which is distinguished slightly from the concept of

a core vs. compatibility prole. A context that is considered forward compatible

basically indicates that all deprecated functionality has been removed. In other

words, if a context is forward compatible, it only includes functions that are in

the core, but not those that were marked as deprecated. A full context supports

all features of the selected version. Some window APIs provide the ability to

select full or forward compatible status along with the prole.

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