OpenGL 4 Shading Language Cookbook

OpenGL 4 Shading Language Cookbook - Second Edition

By : David Wolff, David A Wolff

Buy this Book

OpenGL 4 Shading Language Cookbook - Second Edition

By: David Wolff, David A Wolff

Buy this Book

Overview of this book

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, the language has been further refined to provide programmers with greater power and flexibility, with new stages such as tessellation and compute. OpenGL 4 Shading Language Cookbook provides easy-to-follow examples that first walk you through the theory and background behind each technique, and then go on to provide and explain the GLSL and OpenGL code needed to implement it. Beginner level through to advanced techniques are presented including topics such as texturing, screen-space techniques, lighting, shading, tessellation shaders, geometry shaders, compute shaders, and shadows. OpenGL Shading Language 4 Cookbook is a practical guide that takes you from the fundamentals of programming with modern GLSL and OpenGL, through to advanced techniques. The recipes build upon each other and take you quickly from novice to advanced level code. You'll see essential lighting and shading techniques; 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 including HDR rendering, bloom, and blur; shadowing techniques; tessellation, geometry, and compute shaders; how to use noise effectively; and animation with particle systems. OpenGL Shading Language 4 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.

OpenGL 4 Shading Language Cookbook Second Edition

Credits

About the Author

About the Reviewers

www.PacktPub.com

Preface

Free Chapter

Getting Started with GLSL

Introduction

Using a function loader to access the latest OpenGL functionality

Using GLM for mathematics

Determining the GLSL and OpenGL version

Compiling a shader

Linking a shader program

Sending data to a shader using vertex attributes and vertex buffer objects

Getting a list of active vertex input attributes and locations

Sending data to a shader using uniform variables

Getting a list of active uniform variables

Using uniform blocks and uniform buffer objects

Getting debug messages

Building a C++ shader program class

The Basics of GLSL Shaders

Introduction

Implementing diffuse, per-vertex shading with a single point light source

Implementing per-vertex ambient, diffuse, and specular (ADS) shading

Using functions in shaders

Implementing two-sided shading

Implementing flat shading

Using subroutines to select shader functionality

Discarding fragments to create a perforated look

Lighting, Shading, and Optimization

Introduction

Shading with multiple positional lights

Shading with a directional light source

Using per-fragment shading for improved realism

Using the halfway vector for improved performance

Simulating a spotlight

Creating a cartoon shading effect

Simulating fog

Configuring the depth test

Using Textures

Introduction

Applying a 2D texture

Applying multiple textures

Using alpha maps to discard pixels

Using normal maps

Simulating reflection with cube maps

Simulating refraction with cube maps

Applying a projected texture

Rendering to a texture

Using sampler objects

Image Processing and Screen Space Techniques

Introduction

Applying an edge detection filter

Applying a Gaussian blur filter

Implementing HDR lighting with tone mapping

Creating a bloom effect

Using gamma correction to improve image quality

Using multisample anti-aliasing

Using deferred shading

Implementing order-independent transparency

Using Geometry and Tessellation Shaders

Introduction

Point sprites with the geometry shader

Drawing a wireframe on top of a shaded mesh

Drawing silhouette lines using the geometry shader

Tessellating a curve

Tessellating a 2D quad

Tessellating a 3D surface

Tessellating based on depth

Shadows

Introduction

Rendering shadows with shadow maps

Anti-aliasing shadow edges with PCF

Creating soft shadow edges with random sampling

Creating shadows using shadow volumes and the geometry shader

Using Noise in Shaders

Introduction

Creating a noise texture using GLM

Creating a seamless noise texture

Creating a cloud-like effect

Creating a wood-grain effect

Creating a disintegration effect

Creating a paint-spatter effect

Creating a night-vision effect

Particle Systems and Animation

Introduction

Animating a surface with vertex displacement

Creating a particle fountain

Creating a particle system using transform feedback

Creating a particle system using instanced particles

Simulating fire with particles

Simulating smoke with particles

Using Compute Shaders

Introduction

Implementing a particle simulation with the compute shader

Using the compute shader for cloth simulation

Implementing an edge detection filter with the compute shader

Creating a fractal texture using the compute shader

Index

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Introduction

The OpenGL Shading Language (GLSL) Version 4 brings unprecedented power and flexibility to programmers interested in creating modern, interactive, and graphical programs. It allows us to harness the power of modern Graphics Processing Units (GPUs) in a straightforward way by providing a simple yet powerful language and API. Of course, the first step towards using GLSL is to create a program that utilizes the latest version of the OpenGL API. GLSL programs don't stand on their own; they must be a part of a larger OpenGL program. In this chapter, we will provide some tips and techniques for getting a basic program up and running. First, let's start with some background.

The OpenGL Shading Language

The GLSL is now a fundamental and integral part of the OpenGL API. Going forward, every program written using the OpenGL API will internally utilize one or several GLSL programs. These "mini-programs" are often referred to as shader programs. A shader program usually consists of several components called shaders. Each shader executes within a different section of the OpenGL pipeline. Each shader runs on the GPU, and as the name implies, (typically) implement the algorithms related to the lighting and shading effects of an image. However, shaders are capable of doing much more than just implementing a shading algorithm. They are also capable of performing animation, tessellation, or even generalized computation.

Note

The field of study dubbed GPGPU (General Purpose Computing on Graphics Processing Units) is concerned with utilization of GPUs (often using specialized APIs such as CUDA or OpenCL) to perform general purpose computations such as fluid dynamics, molecular dynamics, cryptography, and so on. With compute shaders, introduced in OpenGL 4.3, we can now do GPGPU within OpenGL.

Shader programs are designed for direct execution on the GPU and are executed in parallel. For example, a fragment shader might be executed once for every pixel, with each execution running simultaneously on a separate GPU thread. The number of processors on the graphics card determines how many can be executed at one time. This makes shader programs incredibly efficient, and provides the programmer with a simple API for implementing highly parallel computation.

The computing power available in modern graphics cards is impressive. The following table shows the number of shader processors available for several models in the NVIDIA GeForce series cards (source: http://en.wikipedia.org/wiki/Comparison_of_Nvidia_graphics_processing_units).

Model	Unified Shader Processors
GeForce GTS 450	192
GeForce GTX 480	480
GeForce GTX 780	2304

Shader programs are intended to replace parts of the OpenGL architecture referred to as the fixed-function pipeline. Prior to OpenGL Version 2.0, the shading algorithm was "hard-coded" into the pipeline and had only limited configurability. This default lighting/shading algorithm was a core part of the fixed-function pipeline. When we, as programmers, wanted to implement more advanced or realistic effects, we used various tricks to force the fixed-function pipeline into being more flexible than it really was. The advent of GLSL will help by providing us with the ability to replace this "hard-coded" functionality with our own programs written in GLSL, thus giving us a great deal of additional flexibility and power. For more details on the programmable pipeline, see the introduction to Chapter 2, The Basics of GLSL Shaders.

In fact, recent (core) versions of OpenGL not only provide this capability, but they require shader programs as part of every OpenGL program. The old fixed-function pipeline has been deprecated in favor of a new programmable pipeline, a key part of which is the shader program written in GLSL.

Profiles – Core vs. Compatibility

OpenGL Version 3.0 introduced a deprecation model, which allowed for the gradual removal of functions from the OpenGL specification. Functions or features can be marked as deprecated, meaning that they are expected to be removed from a future version of OpenGL. For example, immediate mode rendering using glBegin/glEnd was marked deprecated in version 3.0 and removed in version 3.1.

In order to maintain backwards compatibility, the concept of compatibility profiles was introduced with OpenGL 3.2. A programmer that is writing code intended to be used with a particular version of OpenGL (with older features removed) would use the so-called core profile. Someone who also wanted to maintain compatibility with older functionality could use the compatibility profile.

Note

It may be somewhat confusing that there is also the concept of a forward compatible context, which is distinguished slightly from the concept of a core/compatibility profile. A context that is considered forward compatible basically indicates that all deprecated functionality has been removed. In other words, if a context is forward compatible, it only includes functions that are in the core, but not those that were marked as deprecated. Some window APIs provide the ability to select forward compatible status along with the profile.

The steps for selecting a core or compatibility profile are window system API dependent. For example, in GLFW, one can select a forward compatible, 4.3 core profile using the following code:

glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 4 );
glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

GLFWwindow *window = glfwCreateWindow(640, 480, "Title", NULL, NULL);

All programs in this book are designed to be compatible with a forward compatible OpenGL 4.3 core profile.

OpenGL 4 Shading Language Cookbook - Second Edition

By : David Wolff, David A Wolff

OpenGL 4 Shading Language Cookbook - Second Edition

By: David Wolff, David A Wolff

Overview of this book

Related Content you might be interested in

Current Title:

OpenGL 4 Shading Language Cookbook - Second Edition

Introduction

The OpenGL Shading Language

Note

Profiles – Core vs. Compatibility

Note