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Author's note: Keep in mind that although this article is being published on GameDev.net in April 2003, it was written in April 2002, and some things have changed in the past year, notably the release of the OpenGL 1.4 specification, and the standardization of pixel and vertex shaders. I've chosen not to update the article to reflect these changes because I wanted to keep the text consistent with what was published in the book, and because they really make no difference as far as the the purpose of the article is concerned. Introduction Once you've been programming with OpenGL for Windows for a while, you'll probably notice something: the headers and libraries you're using are old. Dig around in the gl.h header, and you'll see this: #define GL_VERSION_1_1 1 This means that you're using OpenGL 1.1, which was released in 1996. In the world of graphics, that's ancient! If you've been paying attention, you know that the current OpenGL specification is at 1.3 (at least at the time of this writing). OpenGL 1.4 should be released later this year, with 2.0 following soon after. Obviously, you need to update your OpenGL headers and libraries to something more recent. As it turns out, the most recent headers and libraries for Windows correspond to … OpenGL 1.1. That's right, the files you already have are the most recent ones available. This, of course, presents a problem. Although you can do some impressive things with OpenGL 1.1, to take full advantage of modern consumer graphics hardware, you're going to need functionality available through more recent versions, as well as features available through extensions (but we'll get to that in a bit). The question, then, is how to access newer features, when your headers and libraries are stuck at OpenGL 1.1. The purpose of this article is to answer that question. What You Will Learn In this article, I will: Explain in greater detail why you need to take some extra steps to use anything beyond OpenGL 1.1. Explain OpenGL's extension mechanism, and how it can be used to access OpenGL 1.2 and 1.3 functionality. Give you an overview of the new options available in OpenGL 1.2 and 1.3, as well as a look at some of the most useful extensions. Give you some tips for using extensions while ensuring that your game will run well on a wide range of systems. Provide a demo showing you how to use the techniques described. The Problem If you're new to OpenGL or have only ever needed the functionality offered in OpenGL 1.1, you may be confused about what the problem is, so let's clarify. To develop for a given version of OpenGL on Windows, you need three things. First, you need a set of libraries (i.e. opengl32.lib and possibly others such as glu32.lib) and headers (i.e. gl.h, and so on) corresponding to the version you'd like to use. These headers and libraries contain the OpenGL functions, constants, and other things you need to be able to compile and link an OpenGL application. Second, the system you intend to run the application on needs to have an OpenGL dynamic link library (OpenGL32.dll), or OpenGL runtime library. The runtime needs to be for either the same or a more recent version of OpenGL as the headers and libraries you're using. Ideally, you will also have a third component, called an Installable Client Driver (IDC). An IDC is provided by the video card drivers to allow for hardware acceleration of OpenGL features, as well as possible enhancements provided by the graphics vendor. So, let's look at these three things and see why you have to jump through a few hoops to use anything newer than OpenGL 1.1: Headers and libraries. As I mentioned in the introduction, the latest version of the OpenGL headers and libraries available from Microsoft correspond to version 1.1. If you look around on the Internet, you may come across another OpenGL implementation for Windows created by Silicon Graphics. SGI's implementation also corresponds to OpenGL 1.1. Unfortunately, this implementation is no longer supported by SGI. In addition, the Microsoft implementation is based upon it, so you really gain nothing by using it. Where does that leave us? Well, there is reason to hope that someone will release up to date libraries. Although, to my knowledge, no one has committed to doing so, several parties have discussed it. Microsoft is the obvious candidate, and despite years of promising and not delivering, it appears that they have taken an interest in the recently proposed OpenGL 2.0. Whether or not that interest will lead to action remains to be seen, but given the large number of graphics workstations running Windows NT and Windows 2000, it's not beyond the realm of possibility. Besides Microsoft, there has apparently been discussion among the members of OpenGL's Architectural Review Board (ARB) to provide their own implementation of the headers and libraries. At present, though, this is still in the discussion stage, so it may be a while before we see anything come of it. The runtime. Most versions of Windows (the first release of Windows 95 being the exception) come with a 1.1 runtime. Fortunately, this isn't really as important as the other elements. All that the runtime does is guarantee a baseline level of functionality, and allow you to interface with the ICD. The ICD. This is the one area where you're okay. Most hardware vendors (including NVIDIA and ATI) have been keeping up with the latest OpenGL standard. For them to be able to advertise that their drivers are compliant with the OpenGL 1.3 standard, they have to support everything included in the 1.3 specification (though not necessarily in hardware). The cool thing about this is that the ICD contains the code to do everything in newer versions of OpenGL, and we can take advantage of that. The thing that's important to note here is that although the headers and libraries available don't directly allow you to access newer OpenGL features, the features do exist in the video card drivers. You just need to find a way to access those features in our code. We do that by using OpenGL's extension mechanism. This article originally appeared in the book Game Programming Tricks of the Trade, 2002, Premier Press. Many members of the GameDev.net community, including several GDNet staff members, contributed to the book, so you're encouraged to check it out. OpenGL Extensions

Contents   Introduction   OpenGL Extensions   Using Extensions   OpenGL 1.2 and 1.3   Writing Well-Behaved Programs   Demo & Conclusion   Source code   Printable version   Discuss this article