Description of how OpenGL on Linux works

I have found an interesting document on this site. It’s a description how OpenGL works on linux with all its driver and libraries…

— Definitions

People frequently get confused by the proliferation of acronyms surrounding OpenGL support on Linux. This document is a vain hope to reduce the confusion. Definitions are given in expository order rather than alphabetical; hopefully by the end you will understand better.

Hey, I can dream.

I’m focusing on Linux 2.6.

OpenGL: 3D graphics specification from SGI, descended from an earlier product called IRIS GL, competitor of Direct3D and QuickDraw3D (deceased). Frequently abbreviated “GL”, particularly on Linux, since “OpenGL” is a trademark, and use of the trademark requires passing a (non-free) conformance suite.

GLX: GL is a graphics language, not a windowing system. “GLX” refers to the extension that binds GL to the X11 window system, enabling 3D drawing on X windows. GLX is an extension to the X protocol. There are similar bindings for other window systems too – WGL on Windows, AGL on MacOS. In X, the client side GLX library is called libGL, and the server side extension is called libglx.

Direct rendering: There are two ways a GL program can get its drawing done. Either the client can do the drawing itself, or it can pass the GL requests to the server and have the server do the drawing. Server-side rendering is called “indirect rendering”, and client-side rendering is called “direct rendering”. Direct rendering is usually faster. This is especially true for Xorg, where the server’s indirect renderer is entirely done in software.

DRI: The Direct Rendering Infrastructure is a technology that enables direct rendering for GL programs on Linux and BSD operating systems.

Mesa: Mesa is a work-alike implementation of GL written by Brian Paul and dozens of contributors. It contains a software rasterizer, a GL state machine, and bindings to several window systems including X and Win32. All the open-source DRI drivers are based on Mesa, as well as several closed-source DRI drivers.

DRI driver: This is where all the excitement happens. The DRI driver is responsible for programming the 3D hardware. Usually DRI drivers use the Mesa state machine. In the DRI, the GLX client-side library loads a DRI driver, named

DRM driver: This is the kernel-side component of the DRI. The DRM is responsible for security and handling resource contention. Not particularly interesting, but mandatory. These are named something.ko in Linux 2.6.

DDX driver: This is a part of the X server, responsible for the other sorts of X drawing like Render and Xv. The DDX has to be DRI-aware, but otherwise not much GL-related happens in the DDX.

AGP: AGP is a fast version of the PCI local bus, with additional features for graphics hardware. The core AGP kernel module is called agpgart.ko.

AGP chipset: Different motherboards have different chipsets and thus different implementations of the AGP feature set. You need the one corresponding to your motherboard chipset. This is probably not always the same as your video chipset. Via chipsets need via-agp.ko, etc.


2 Responses to “Description of how OpenGL on Linux works”

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  2. stefon Says:

    this looks like spam, but i checked it, its a useful site *g*

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