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

Discarding fragments to create a perforated look


Fragment shaders can make use of the discard keyword to "throw away" fragments. Use of this keyword causes the fragment shader to stop execution, without writing anything (including depth) to the output buffer. This provides a way to create holes in polygons without using blending. In fact, since fragments are completely discarded, there is no dependence on the order in which objects are drawn, saving us the trouble of doing any depth sorting that might have been necessary if blending was used.

In this recipe, we'll draw a teapot, and use the discard keyword to remove fragments selectively based on texture coordinates. The result will look like the following image:

Getting ready

The vertex position, normal, and texture coordinates must be provided to the vertex shader from the OpenGL application. The position should be provided at location 0, the normal at location 1, and the texture coordinates at location 2. As in previous examples, the lighting...