3.5. What is DRI?
Graphics rendering has 3 players: the client application (like Quake 3), the X server and the hardware (the graphics card). Previously, client applications were prohibited from writing directly to hardware, and there was a good reason for this. A program that is allowed to directly write to hardware can crash the system in any number of ways. Rather than trusting programmers to write totally bug free, cooperative programs that access hardware, Linux simply disallowed it. However, that changed under X 4.x with DRI (Direct Rendering Infrastructure <http://www.dri.sourceforge.net >. DRI allows X clients to write 3D rendering information directly to the video card in a safe and cooperative manner.
DRI gets the X server out of the way so the 3D driver (Mesa or OpenGL) can talk directly to the hardware. This speeds things up. The 3D rendering information doesn't even have to be hardware accelerated. On a technical note, this has a number of virtues.
Vertex data doesn't have to be encoded/decoded via GLX.
Graphics data isn't sent over a socket to the X server.
On uni-processor machines the CPU doesn't have to change context between XFree86 and its client to render the graphics.
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