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)

Execution model

When a primitive stage has ended, its processing in the vertex primitive stages (vertex shaders, geometry shaders, and clipping) becomes rasterized. The fragment shader execution begins this rasterization.

Consider a triangle; in order to paint that triangle onto the screen you need to convert it from its native vectorial form (vertices coordinate) to discrete pixels. The system that carries out that action is the fragment shader module, being executed once per each fragment.

The more of the framebuffer's area the primitive covers, the more times the fragment shader will be executed. The fragment shaders' performance has direct influence on your application's fill rate (the speed at which the GPU can output fragments).

Having said that, let's see two very important constraints about fragment shaders:

  • A fragment shader can't read the framebuffer. It's only capable of writing into it. If you need to mix your framebuffer with the result of your fragment shader computations, you...