Book Image

GLSL Essentials

By : Jacobo Rodriguez
Book Image

GLSL Essentials

By: Jacobo Rodriguez

Overview of this book

Shader programming has been the largest revolution in graphics programming. OpenGL Shading Language (abbreviated: GLSL or GLslang), is a high-level shading language based on the syntax of the C programming language.With GLSL you can execute code on your GPU (aka graphics card). More sophisticated effects can be achieved with this technique.Therefore, knowing how OpenGL works and how each shader type interacts with each other, as well as how they are integrated into the system, is imperative for graphic programmers. This knowledge is crucial in order to be familiar with the mechanisms for rendering 3D objects. GLSL Essentials is the only book on the market that teaches you about shaders from the very beginning. It shows you how graphics programming has evolved, in order to understand why you need each stage in the Graphics Rendering Pipeline, and how to manage it in a simple but concise way. This book explains how shaders work in a step-by-step manner, with an explanation of how they interact with the application assets at each stage. This book will take you through the graphics pipeline and will describe each section in an interactive and clear way. You will learn how the OpenGL state machine works and all its relevant stages. Vertex shaders, fragment shaders, and geometry shaders will be covered, as well some use cases and an introduction to the math needed for lighting algorithms or transforms. Generic GPU programming (GPGPU) will also be covered. After reading GLSL Essentials you will be ready to generate any rendering effect you need.
Table of Contents (13 chapters)

Geometry shaders versus vertex shaders

Although geometry shaders transform vertices in a very similar way than vertex shaders do, we have to enumerate some important differences between them:

  • Vertex shaders are executed once by an incoming vertex. Geometry shaders are executed once (by default) by an incoming primitive.

  • Vertex shaders can't access any information about adjacent vertices. A geometry shader has all the information for a given primitive and adjacent ones.

  • Vertex shaders don't produce new vertices. Geometry shaders create new primitives (in fact, that's the main purpose).

In addition, there are other facts about geometry shaders that must be known:

  • The geometry shader stage happens after the primitive assembly stage.

  • A geometry shader receives assembled primitives. This means that it doesn't matter if you send triangles, triangle strips, or fans of triangles. A geometry shader will always receive a triangle. The same happens with lines, line strips, or line loops. The primitives that...