OpenGL vs. DirectX: A Comparison

The competition between OpenGL and DirectX is possibly as well known as the wars waged between AMD and Intel enthusiasts. This topic has sparked the fires of many flame wars throughout the years, and I don't anticipate that changing anytime soon. I won't preach why I prefer OpenGL over DirectX, but rather lay out the facts and let you make that decision. So let's dive in!
Perhaps the most obvious difference is that DirectX, as opposed to OpenGL, is more than just a graphics API. DirectX contains tools to deal with such components of a game as sound, music, input, networking, and multimedia. On the other hand, OpenGL is strictly a graphics API. So what aspect of OpenGL sets it apart from the DirectX graphics component?

Well, first things first: both APIs rely on the use of the traditional graphics pipeline. This is the same pipeline that has been used in computer games since the early days of computer graphics. Although it has been modified in slight ways to adapt with advancements in hardware, the basic idea remains intact.

Both OpenGL and DirectX describe vertices as a set of data consisting of coordinates in space that define the vertex location and any other vertex related data. Graphics primitives, such as points, lines, and triangles, are defined as an ordered set of vertices. There is a difference in how each API handles how vertices are combined to form primitives.

There are a bunch of differences in the DirectX and OpenGL APIs, so I will list a few of those for you. This chart is based off the book, OpenGL Game Programming and a few of these may now be incorrect as new DirectX versions are released. If you wish to correct me, please do via one of the ways listed at the end of this tutorial.

Table 1.1:

Feature:	OpenGL	DirectX
Vertex Blending	N/A	Yes
Multiple Operating Systems	Yes	No
Extension Mechanism	Yes	Yes
Development	Multiple member Board	Microsoft
Thorough Specification	Yes	No
Two-sided lighting	Yes	No
Volume Textures	Yes	No
Hardware independent Z-buffers	Yes	No
Accumulation buffers	Yes	No
Full-screen Antialiasing	Yes	Yes
Motion Blur	Yes	Yes
Depth of field	Yes	Yes
Stereo Rendering	Yes	No
Point-size/line-width attributes	Yes	No
Picking	Yes	No
Parametric curves and surfaces	Yes	No
Cache geometry	Display Lists	Vertex Buffers
System emulation	Hardware not present	Let app determine
Interface	Procedure calls	COM
Updates	Yearly	Yearly
Source Code	Sample	SDK Implementation

So now you know what separates DirectX and OpenGL, and hopefully you have chosen based on facts which you would prefer, not on myths or opinions. I hope you chose OpenGL, as that's what I will be teaching. If you chose DirectX my tutorials won't help you very much. In the next lesson we will begin with our first OpenGL program.
Until next time, happy coding! 

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