Book Image

OpenGL 4 Shading Language Cookbook - Third Edition

By : David Wolff
Book Image

OpenGL 4 Shading Language Cookbook - Third Edition

By: David Wolff

Overview of this book

OpenGL 4 Shading Language Cookbook, Third Edition provides easy-to-follow recipes that first walk you through the theory and background behind each technique, and then proceed to showcase and explain the GLSL and OpenGL code needed to implement them. The book begins by familiarizing you with beginner-level topics such as compiling and linking shader programs, saving and loading shader binaries (including SPIR-V), and using an OpenGL function loader library. We then proceed to cover basic lighting and shading effects. After that, you'll learn to use textures, produce shadows, and use geometry and tessellation shaders. Topics such as particle systems, screen-space ambient occlusion, deferred rendering, depth-based tessellation, and physically based rendering will help you tackle advanced topics. OpenGL 4 Shading Language Cookbook, Third Edition also covers advanced topics such as shadow techniques (including the two of the most common techniques: shadow maps and shadow volumes). You will learn how to use noise in shaders and how to use compute shaders. The book 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 (17 chapters)
Title Page
Packt Upsell

Using alpha maps to discard pixels

To create the effect of an object that has holes, we could use a texture with an appropriate alpha channel that contains information about the transparent parts of the object. However, that requires us to make the depth buffer read-only and render all of our polygons from back to front in order to avoid blending problems. We would need to sort our polygons based on the camera position and then render them in the correct order. What a pain! With GLSL shaders, we can avoid all of this by using the discard keyword to completely discard fragments when the alpha value of the texture map is below a certain value. By completely discarding the fragments, there's no need to modify the depth buffer because when discarded, they aren't evaluated against the depth buffer at all. We don't need to depth-sort our polygons because there is no blending.

The following image on the right shows a teapot with fragments discarded based upon the texture on the left. The fragment...