How is Mesa different from OpenGL drivers?

Question

What exactly does it mean to say that Mesa is an implementation of OpenGL? Don't the drivers of my Nvidia card implement all the OpenGL functions, etc.? So given that the drivers of my Nvidia card are taking Opengl calls and handing them off to the hardware, what exactly does Mesa do? Can someone clarify the distinction between Mesa and drivers?

Answer 1

Can someone clarify the distinction between Mesa and drivers?

Mesa provides the client side OpenGL interface for the open source GPU drivers based on the DRI2/DRM architecture. Or in other words: It's also a part of a driver.

If you've got the proprietary drivers from NVidia or AMD installed you don't need Mesa. If you want to use the open source drivers (nouveau, radeon, radeonhd, intel) you need Mesa.

Answer 2

I believe LinuxQuestions.org forum member geeman2.0 provided a good explanation for this matter:

OpenGL and Mesa aren't really two separate choices, but rather Mesa is a specific type of OpenGL.

OpenGL is simply an interface that defines a standard set of functions needed for drawing 3d graphics. It doesn't involve the actual code that makes these functions happen, it only specifies what the functions are called and what they are supposed to do.

An openGL implementation provides the actual code that runs the methods specified by the OpenGL standard. Without an implementation installed, you cannot run any opengl programs.

Mesa is just one of many OpenGL implementations, and is the most standard one included in linux distributions. It does all the work in software, which is why it is slow.

When you install Nvidia or ATI drivers for a fancy graphics card, these drivers provide a new OpenGL implementation that runs on the graphics card. This implementation would take the place of the Mesa implementation, but it is still an openGL implementation. That is, all of Mesa/ATI/NVidia drivers implement the same set of functions, they just do it in different ways, and they are all openGL.

Source

Answer 3

What exactly does it mean to say that Mesa is an implementation of OpenGL?

First of all, OpenGL is an API Specification created between Khronos and the videocard manufacturer (Nvidia, ATI, Intel, etc), it's like an agreement on what functions the hardware is capable of.

Mesa is a software library for 3D computer graphics that provides a generic Khronos-compliant OpenGL implementation for rendering three-dimensional graphics on multiple platforms. So, for example, if you are running Linux you will probably have to install Mesa in order to generate any kind of graphics. For Microsoft Windows there is already an implementation installed.

Don't the drivers of my Nvidia card implement all the OpenGL functions, etc.?

Yes, your Nvidia card driver implements OpenGL functions.

So given that the drivers of my Nvidia card are taking Opengl calls and handing them off to the hardware, what exactly does Mesa do?

Your program communicates to Mesa, Mesa to your video card's driver, the driver to the actual GPU, the GPU sends the signal to the monitor for you to finally watch the drawing.