OpenGL 4.0 Shading Language Cookbook

Table of Contents

OpenGL 4.0 Shading Language Cookbook

Credits

About the Author

About the Reviewers

www.PacktPub.com

Support files, eBooks, discount offers and more

Why subscribe?

Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code for this book

Errata

Piracy

Questions

1. Getting Started with GLSL 4.0

Introduction

The OpenGL Shading Language

Profiles: Core vs. Compatibility

Using the GLEW Library to access the latest OpenGL functionality

Getting ready

How to do it...

How it works...

There's more...

GLEW visualinfo

GLEW glewinfo

Checking for extension availability at runtime

See also

Using the GLM library for mathematics

Getting ready

How to do it...

How it works...

There's more...

Using the GLM types as input to OpenGL

See also

Determining the GLSL and OpenGL version

How to do it...

How it works...

There's more...

See also

Compiling a shader

Getting ready

How to do it...

How it works...

There's more...

Deleting a shader object

See also

Linking a shader program

Getting ready

How to do it...

How it works...

There's more...

Deleting a shader program

See also

Sending data to a shader using per-vertex attributes and vertex buffer objects

Getting ready

How to do it...

How it works...

There's more...

Using layout qualifiers

Using element arrays

Interleaved arrays

See also

Getting a list of active vertex input attributes and indices

Getting ready

How to do it...

How it works...

There's more...

See also

Sending data to a shader using uniform variables

Getting ready

How to do it...

How it works...

There's more...

See also

Getting a list of active uniform variables

Getting ready

How to do it...

How it works...

There's more...

See also

Using uniform blocks and uniform buffer objects

Getting ready

How to do it...

How it works...

There's more...

Using an instance name with a uniform block

Using layout qualifiers with uniform blocks

See also

Building a C++ shader program class

Getting ready

How to do it...

How it works...

See also

2. The Basics of GLSL Shaders

Introduction

Vertex and fragment shaders

Replicating the old fixed functionality

Implementing diffuse, per-vertex shading with a single point light source

Getting ready

How to do it...

How it works...

There's more...

See also

Implementing per-vertex ambient, diffuse, and specular (ADS) shading

Getting ready

How to do it...

How it works...

There's more...

Using a non-local viewer

Per-vertex vs. Per-fragment

Directional lights

Light attenuation with distance

See also

Using functions in shaders

Getting ready

How to do it...

How it works...

There's more...

The const qualifier

Function overloading

Passing arrays or structures to a function

See also

Implementing two-sided shading

Getting ready

How to do it...

How it works...

There's more...

Using two-sided rendering for debugging

See also

Implementing flat shading

How to do it...

How it works...

See also

Using subroutines to select shader functionality

Getting ready

How to do it...

How it works...

There's more...

See also

Discarding fragments to create a perforated look

Getting ready

How to do it...

How it works...

See also

3. Lighting, Shading Effects, and Optimizations

Introduction

Shading with multiple positional lights

Getting ready

How to do it...

How it works...

See also

Shading with a directional light source

Getting ready

How to do it...

How it works...

There's more...

See also

Using per-fragment shading for improved realism

Getting ready

How to do it...

How it works...

There's more...

See also

Using the halfway vector for improved performance

Getting ready

How to do it...

How it works...

There's more...

See also

Simulating a spotlight

Getting ready

How to do it...

How it works...

See also

Creating a cartoon shading effect

Getting ready

How to do it...

How it works...

There's more...

See also

Simulating fog

Getting ready

How to do it...

How it works...

There's more...

Computing distance from the eye

See also

4. Using Textures

Introduction

Applying a 2D texture

Getting ready

How to do it...

How it works...

There's more...

See also

Applying multiple textures

Getting ready

How to do it...

How it works...

There's more...

See also

Using alpha maps to discard pixels

Getting ready

How to do it...

How it works...

There's more...

See also

Using normal maps

Getting ready

How to do it...

How it works...

See also

Simulating reflection with cube maps

Getting ready

How to do it...

How it works...

There's more...

See also

Simulating refraction with cube maps

Getting ready

How to do it...

How it works...

There's more...

The Fresnel equations

Chromatic aberration

Both sides of the object?

See also

Image-based lighting

Getting ready

How to do it...

How it works...

There's more...

See also

Applying a projected texture

Getting ready

How to do it...

How it works...

There's more...

See also

Rendering to a texture

Getting ready

How to do it...

How it works...

There's more...

See also

5. Image Processing and Screen Space Techniques

Introduction

Applying an edge detection filter

Getting ready

How to do it...

How it works...

There's more...

Optimization techniques

See also

Applying a Gaussian blur filter

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a bloom effect

Getting ready

How to do it...

How it works...

There's more...

Using low-res textures

See also

Using gamma correction to improve image quality

How to do it...

How it works...

There's more...

Using multisample anti-aliasing

Getting ready

How to do it...

How it works...

There's more...

Using deferred shading

Getting ready

How to do it...

How it works...

There's more...

See also

6. Using Geometry and Tessellation Shaders

Introduction

The shader pipeline extended

The geometry shader

The tessellation shaders

Point sprites with the geometry shader

Getting ready

How to do it...

How it works...

There's more...

Drawing a wireframe on top of a shaded mesh

Getting ready

How to do it...

How it works...

There's more...

See also

Drawing silhouette lines using the geometry shader

Getting ready

How to do it...

How it works...

There's more...

See also

Tessellating a curve

Getting ready

How to do it...

How it works...

There's more...

Tessellating a 2D quad

Getting ready

How to do it...

How it works...

See also

Tessellating a 3D surface

Getting ready

How to do it...

How it works...

See also

Tessellating based on depth

Getting ready

How to do it...

How it works...

There's more...

See also

7. Shadows

Introduction

Rendering shadows with shadow maps

Getting ready

How to do it...

How it works...

There's more...

Aliasing

Rendering back faces only for the shadow map

See also

Anti-aliasing shadow edges with PCF

Getting ready

How to do it...

How it works...

There's more...

See also

Creating soft shadow edges with random sampling

Getting ready

How to do it...

How it works...

There's more...

See also

Improving realism with prebaked ambient occlusion

Getting ready

How to do it...

How it works...

There's more...

Screen-space ambient occlusion

Another technique for dynamic ambient occlusion

8. Using Noise in Shaders

Introduction

Creating a noise texture using libnoise

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a seamless noise texture

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a cloud-like effect

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a wood grain effect

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a disintegration effect

Getting ready

How to do it...

How it works...

See also

Creating a paint-spatter effect

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a night-vision effect

Getting ready

How to do it...

How it works...

There's more...

See also

9. Animation and Particles

Introduction

Animating a surface with vertex displacement

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a particle fountain

Getting ready

How to do it...

How it works...

There's more...

See also

Creating a particle system using transform feedback

Getting ready

How to do it...

How it works...

There's more...

Querying transform feedback results

Recycling particles

See also

Creating a particle system using instanced particles

Getting ready

How to do it...

How it works...

There's more...

See also

Simulating fire with particles

Getting ready

How to do it...

How it works...

There's more...

See also

Simulating smoke with particles

Getting ready

How to do it...

How it works...

See also

Index

OpenGL 4.0 Shading Language Cookbook

OpenGL 4.0 Shading Language Cookbook

Copyright © 2011 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: July 2011

Production Reference: 1180711

Published by Packt Publishing Ltd.

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ISBN 978-1-849514-76-7

www.packtpub.com

Cover Image by Fillipo (<filosarti@tiscali.it>)

Credits

Author

David Wolff

Reviewers

Martin Christen

Nicolas Delalondre

Markus Pabst

Brandon Whitley

Acquisition Editor

Usha Iyer

Development Editor

Chris Rodrigues

Technical Editors

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Copy Editor

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Project Coordinator

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Proofreader

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Indexer

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Graphics

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Production Coordinators

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Cover Work

Kruthika Bangera

About the Author

David Wolff is an associate professor in the Computer Science and Computer Engineering Department at Pacific Lutheran University (PLU). He received his PhD in Physics from Oregon State University. He has a passion for computer graphics and the intersection between art and science. He has been teaching computer graphics to undergraduates at PLU for over 10 years, using OpenGL.

Special thanks to Brandon Whitley for interesting discussions and helpful insights during the writing of this book. His help has been incredibly valuable. Thanks also to all of the reviewers and editors for their help.

I'd also like to thank my parents for a lifetime of support, love and encouragement.

About the Reviewers

Martin Christen graduated with a Computer Science degree. Today, he is a senior research associate at the Institute of Geomatics Engineering of the University of Applied Sciences Northwestern (FHNW) Switzerland. He is the lead developer of the open source virtual globe engine (http://www.openwebglobe.org).

Previously, he was software developer in the fields of 3D geoinformation and in 3D computer game development. His main research interests are GPU-programming, parallel computing, terrain-rendering, and 3D graphics engine architecture.

Nicolas Delalondre has been working on 3D computer graphics software for more than ten years mainly in OpenGL on desktop and mobile devices. Currently, he is a freelance developer at Digital Mind and an associate at Rhino Terrain where he develops geomodeling and meshing algorithms. Before joining Rhino Terrain, Nicolas was a 3D software engineer at Bionatics, a French startup, developing OpenGL engine and algorithms for geographic information system (GIS). Prior to working with Bionatics, he worked for INRIA (French research institute in computer science) in the radiosity field. Nicolas has a Master's degree in Computer Science from EFREI, France.

Markus Pabst has been working with OpenGL since 2002. He works in the digital mapping industry and has worked with the desktop and embedded versions of OpenGL. Since 2007, he has been leading a team of software engineers developing an embedded OpenGL-based cockpit display system for the Airbus A400M aircraft certified against DO-178B Level C standard. In 2005, he began teaching OpenGL at the German University of Applied Sciences Ravensburg-Weingarten.

Markus received his university degree in Multimedia Technologies from the Technical University of Ilmenau, in 2002. In the summer, you may find Markus on a sailing boat in southern Germany.

Brandon Whitley worked for four years as a graphics programmer for Zipper Interactive, a Sony Computer Entertainment Worldwide Studio. He earned his Masters degree in Computer Science from Georgia Institute of Technology. While obtaining his undergraduate degree at Pacific Lutheran University, he was inspired by the author of this book to pursue a career in computer graphics. Brandon is currently a graphics programmer at Bungie, creators of the Halo series.

I would like to thank my wife, Katie, and my son, Parker, for their love 
and support.

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Preface

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

The OpenGL 4.0 Shading Language Cookbook will provide easy-to-follow examples that start by walking you through the theory and background behind each technique. It then goes on to provide and explain the GLSL and OpenGL code needed to implement them. Beginning through to advanced techniques are presented, including topics such as texturing, screen-space techniques, lighting, shading, tessellation shaders, geometry shaders, and shadows.

What this book covers

Chapter 1, Getting Started with GLSL 4.0, provides tips and tricks for setting up your OpenGL development environment to take advantage of the latest OpenGL and GLSL language features. It also teaches the basic techniques for communicating with shader programs.

Chapter 2, The Basics of GLSL Shaders, provides examples of basic shading techniques such as diffuse shading, two-sided shading, and flat shading. It also discuses an example of a new 4.0 language feature: subroutines.

Chapter 3, Lighting and Shading Effects and Optimizations, provides examples of more complex lighting and shading such as multiple lights, per-fragment shading, spotlights, cartoon shading, and fog. It moves further to explain how to gain a slight increase in execution speed by using the halfway vector or a directional light source.

Chapter 4, Using Textures, provides a variety of examples illustrating how textures can be used in GLSL shaders. It also explores examples involving simple 2D textures, multiple textures, normal maps, alpha maps, cube maps, and projected textures. It also discusses how to render to a texture using framebuffer objects.

Chapter 5, Image Processing and Screen Space Techniques, discusses various techniques to apply post-processing effects such as bloom, blur, and edge detection. It also discusses an example of a very popular rendering technique known as deferred shading.

Chapter 6, Using Geometry and Tessellation Shaders, provides a series of examples to introduce you to the new and powerful segments of the shader pipeline. It provides some examples of geometry shaders, and discusses how to use tessellation shaders to dynamically render geometry at different levels of detail.

Chapter 7, Shadows, provides several recipes surrounding the shadow-mapping algorithm. It also discusses some basic and advanced techniques for producing shadows, focusing mainly on texture-based shadow maps.

Chapter 8, Using Noise in Shaders, provides recipes that demonstrate how to make use of a pre-computed noise texture to create a variety of effects. The first two recipes demonstrate how to generate a noise texture using the free, open-source library libnoise. Then, it moves on to explain several examples that use noise textures to produce natural and artificial effects such as wood grain, clouds, electrical interference, splattering, and erosion.

Chapter 9, Animation and Particles, discusses several examples of animation within shaders, focusing mostly on particle systems. It also provides an example illustrating how to use OpenGL's transform feedback functionality within a particle system. The last two recipes in the chapter demonstrate some particle systems for simulating complex real systems, such as smoke and fire.

What you need for this book

You will need familiarity with OpenGL programming, along with an understanding of the typical 3D coordinate systems, projections, and transformations.

Who this book is for

This book is for OpenGL programmers who would like to take advantage of the modern features of GLSL 4.0 to create real-time, three-dimensional graphics. It can also be useful for experienced GLSL programmers who are looking to implement the techniques that are presented here.

Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: The ambient component is computed and stored in the variable named ambient.

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.

Note

Warnings or important notes appear in a box like this.

Tip

Tips and tricks appear like this.

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Questions

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Chapter 1. Getting Started with GLSL 4.0

In this chapter, we will cover:

Using the GLEW library to access the latest OpenGL functionality

Using the GLM library for mathematics

Determining the GLSL and OpenGL version

Compiling a shader

Linking a shader program

Sending data to a shader using per-vertex attributes and vertex buffer objects

Getting a list of active vertex input attributes and indices

Sending data to a shader using uniform variables

Getting a list of active uniform variables

Using uniform blocks and uniform buffer objects

Building a C++ shader program class

Introduction

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

Note

The field 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 fluid 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 efficient, 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).

Shader programs are intended to replace parts of the OpenGL architecture referred to as the fixed-function pipeline . The default lighting/shading algorithm was a core part of this fixed-function pipeline. When we, as programmers, wanted to implement more advanced or realistic effects, we used various tricks to force the fixed-function pipeline into being more flexible 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 flexibility 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 fixed-function pipeline has been deprecated in favor of a new programmable pipeline, a key part of which is the shader program written in GLSL.

Profiles: Core vs. Compatibility

OpenGL version 3.0 introduced a deprecation model, which allowed for the gradual removal of functions from the OpenGL specification. 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 profiles 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 profile . Someone who also wanted to maintain compatibility with older functionality could use the compatibility profile.

Note

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 profile. 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 profile.

The steps for selecting a core or compatibility profile are window system API dependent. For example, in recent versions of Qt (at least version 4.7), one can select a 4.0 core profile using the following code:

QGLFormat format;

format.setVersion(4,0);

format.setProfile(QGLFormat::CoreProfile);

QGLWidget *myWidget = new QGLWidget(format);

Tip

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You can download the example code files for all Packt books you have purchased from your account at http://www.PacktPub.com. If you purchased this book elsewhere, you can visit http://www.PacktPub.com/support and register to have the files e-mailed directly to you.

All programs in this book are designed to be compatible with an OpenGL 4.0 core profile.

Using the GLEW Library to access the latest OpenGL functionality

The OpenGL ABI (application binary interface) is frozen to OpenGL version 1.1 on Windows. Unfortunately for Windows developers, that means that it is not possible to link directly to functions that are provided in newer versions of OpenGL. Instead, one must get access to these functions by acquiring a function pointer at runtime. Getting access to the function pointers requires somewhat tedious work, and has a tendency to clutter your code. Additionally, Windows typically comes with a standard OpenGL header file that conforms to OpenGL 1.1. The OpenGL wiki states that Microsoft has no plans to update the gl.h and opengl32.lib that comes with their compilers. Thankfully, others have provided libraries that manage all of this for us by probing your OpenGL libraries and transparently providing the necessary function pointers, while also exposing the necessary functionality in its header files. One such library is called GLEW (OpenGL Extension Wrangler).

Getting ready

Download the GLEW distribution from http://glew.sourceforge.net. There are binaries available for Windows, but it is also a relatively simple matter to compile GLEW from source (see the instructions on the website: http://glew.sourceforge.net).

Place the header files glew.h and wglew.h from the GLEW distribution into a proper location for your compiler. If you are using Windows, copy the glew32.lib to the appropriate library directory for your compiler, and place the glew32.dll into a system-wide location, or the same directory as your program's executable. Full installation instructions for all operating systems and common compilers are available on the GLEW website.

How to do it...

To start using GLEW in your project, use the following steps:

Make sure that, at the top of your code, you include the glew.h header before you include the OpenGL header files:

#include

#include

#include

In your program code, somewhere just after the GL context is created (typically in an initialization function), and before any OpenGL functions are called, include the following code:

GLenum err = glewInit();

if( GLEW_OK != err )

{

    fprintf(stderr, Error initializing GLEW: %s\n,

                    glewGetErrorString(err) );

}

That's all there is