Can opengl calls run without a GPU present?

Question

I know that opengl is a library that allows certain tasks/calls (like shading) to be executed on the GPU for faster computation (hardware accelerated). I've been reading on the internet about it and am wondering if calls to opengl will run without a GPU present. For example, someone on this forum ( https://www.gamedev.net/forums/topic/638883-will-opengl-3d-games-run-in-a-pc-without-a-dedicated-video-card/ ) mentioned that it can run as a software emulation. Can anyone speak to this?

Answer 1

Yes, if it all just depends on whether or not the vendor of the device bothered to write OpenGL drivers for his or her system. All OpenGL functions can be implemented without a graphics card, but with a performance penalty, of course.

Answer 2

Strictly speaking OpenGL is not a library but only a programming interface (API). The specific details of how this API is implemented on a particular machine are left open and are at the disposal of the system implementors. It might be a software rasterizer, it might be an interface to dedicated hardware.

OpenGL has been part of the ABI (ie the set of things that applications can be sure of to be available on a system) of Windows, LSB4/Desktop (Linux Standard Base / Desktop requirements) and MacOS. As such the system must make sure that there's always a some way to have at least a minimal set of OpenGL functionality (we're speaking OpenGL-1.x here), even if there's not hardware acceleration for it.

It should be noted that all these ABIs are writting against the assumption, that it is used to render things to a display device:

The Windows fallback software rasterizer implementation (which is horribly slow BTW) does allow rendering to GDI bitmaps, but does not have support for PBuffers; and don't even think about framebuffer objects.

The Mesa software rasterizer is pretty much OpenGL-3.x feature complete.