OpenGL Insights

The Build Syndrome

Jochem van der Spek and Daniel Dekkers

44.1 Introduction

In the current age of desktop, mobile, and console computing, the number of plat-

forms, operating systems, and OpenGL versions that are in active use has become so

large that developing and deploying our application for all those different configura-

tions has become a trying and time-consuming part of development. When a game

studio wants to release its latest title on as many platforms as possible, it needs to

manage a combinatoric explosion of all the different configuration parameters.

We recognize two steps in the process to reduce the complexity of this task.

The first is to write OpenGL agnostic code, meaning that the code encapsulates the

platform- and OpenGL version–specific details into classes that are fully transparent

to any combination of platform and OpenGL version. The second method is to use

a metabuild system that wraps all that code into a usable project for many different

IDEs on many different platforms. Each platform comes with its own set of APIs for

creating a window to draw. Some of these APIs support OpenGL ES for embedded

systems, even on nonembedded desktop platforms such as the iPad simulator on OS

X, while some only support the OpenGL version that is enabled by the OpenGL

drivers on that platform. Different OpenGL implementations on various platforms

can be seen in Table 44.1. A complete list can be found on the OpenGL.org web-

site [Khronos 97]. A completely different way of achieving the same goal is to use

JavaScript with WebGL and is described in detail in Chapter 3. In this article we will

focus on C++/Objective-C.

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636 VII Software Design

OpenGL(1.0–4.2) OpenGL ES(1.0/2.0)

OS X desktop GLUT, QT, wxWidgets, X11 QT

iOS embedded N/A CoreAnimation (iOS 2.0/3.0)

SGI desktop GLUT, QT, X11 EGL

Windows desktop GLUT, QT, wxWidgets, EGL EGL

Windows embedded N/A EGL, QT

Unix desktop GLUT, QT, wxWidgets, EGL EGL

Linux desktop GLUT, QT, wxWidgets, X11, EGL EGL

Linux embedded N/A EGL/QT

Android embedded N/A Android (1.0/2.2), EGL

Symbian embedded N/A EGL, QT

Blackberry embedded N/A BlackberryOS (5.0/7.0)

Web browsers N/A WebGL (ES2.0 only)

Table 44.1. Overview of the main OpenGL implementations on the various platforms.

As a demonstration, we show how to implement a very minimalistic OpenGL

program on a subset of all the possible platforms, as can be seen in Table 44.2.

For the sake of simplicity, we further limit ourselves to considering only APIs that

interface the creation of the so-called OpenGL drawing context, which specifies to

the operating system how a pixel is to be drawn to the screen. See [OpenGL 11] for

a more extensive discussion of this topic.

In describing the use of our selection of APIs on the subset of platforms, we

draw from the experience of writing the RenderTools [RenderTools 11] software li-

brary. The library was created over the course of the past three years (2008–2011)

to serve as a code base to create any conceivable OpenGL application on many dif-

ferent platforms. We tried to keep the classes lightweight: the library, in its sim-

plest form, depends as little as possible on external libraries. We used the whim-

sically named Extension Wrangler Library, or GLEW [Sourceforge 11], to manage

the various OpenGL extensions on each platform. Many deprecated math func-

OpenGL1.0–4.2 OpenGL ES 1.0–2.0

iOS N/A CoreAnimation(iOS 2.0/3.0)

Windows GLUT, QT, EGL EGL

OS X GLUT, QT N/A

Table 44.2. The selection of APIs and subset of platforms used in this article.