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)

Vertex shader outputs

Vertex shaders can output generic values to the next stage. Those values are going to be passed to the geometry shading stage first, then rasterized, and finally passed to the fragment shading stage in one of the allowed interpolation fashions. You can choose the kind of interpolation, but we will use in this book a linear perspective-corrected interpolation.

To specify an output variable, you must use the interpolation type along with the out keyword:

#version 430
#pragma debug(on)
#pragma optimize(off)
layout (location = 0) in vec4 Position;
layout (location = 1) in vec2 TexCoord;

uniform mat4 Modelview;
uniform mat4 Projection;

// smooth = linearly perspective-correct interpolation
smooth out vec2 texCoordsInterpolated;
void main()
  gl_Position = Projection * Modelview * Position;

  // Write the vertex attribute into an output variable that will be interpolated in a later pipeline's stages
  texCoordsInterpolated = TexCoord;