Book Image

OpenGL 4.0 Shading Language Cookbook

Book Image

OpenGL 4.0 Shading Language Cookbook

Overview of this book

The OpenGL Shading Language (GLSL) is a programming language used for customizing parts of the OpenGL graphics pipeline that were formerly fixed-function, and are executed directly on the GPU. It provides programmers with unprecedented flexibility for implementing effects and optimizations utilizing the power of modern GPUs. With version 4.0, the language has been further refined to provide programmers with greater flexibility, and additional features have been added such as an entirely new stage called the tessellation shader. The OpenGL Shading Language 4.0 Cookbook provides easy-to-follow examples that first walk you through the theory and background behind each technique then go on to provide and explain the GLSL and OpenGL code needed to implement it. Beginning level through to advanced techniques are presented including topics such as texturing, screen-space techniques, lighting, shading, tessellation shaders, geometry shaders, and shadows. The OpenGL Shading Language 4.0 Cookbook is a practical guide that takes you from the basics of programming with GLSL 4.0 and OpenGL 4.0, through basic lighting and shading techniques, to more advanced techniques and effects. It presents techniques for producing basic lighting and shading effects; examples that demonstrate how to make use of textures for a wide variety of effects and as part of other techniques; examples of screen-space techniques, shadowing, tessellation and geometry shaders, noise, and animation. The OpenGL Shading Language 4.0 Cookbook provides examples of modern shading techniques that can be used as a starting point for programmers to expand upon to produce modern, interactive, 3D computer graphics applications.
Table of Contents (16 chapters)
OpenGL 4.0 Shading Language Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

Using subroutines to select shader functionality


In GLSL, a subroutine is a mechanism for binding a function call to one of a set of possible function definitions based on the value of a variable. In many ways it is similar to function pointers in C. A uniform variable serves as the pointer and is used to invoke the function. The value of this variable can be set from the OpenGL side, thereby binding it to one of a few possible definitions. The subroutine's function definitions need not have the same name, but must have the same number and type of parameters and the same return type.

Subroutines therefore provide a way to select alternate implementations at runtime without swapping shader programs and/or recompiling, or using if statements along with a uniform variable. For example, a single shader could be written to provide several shading algorithms intended for use on different objects within the scene. When rendering the scene, rather than swapping shader programs (or using a conditional...