legacy GL vs GLVND Open GL

JoeCFD

Maybe a dumb question.
I noticed that Qt OpenGL lib is linked to legacy GL instead of GLVND Open GL. Is not GLVND Open GL better than legacy GL?

SGaist

Hi,

What do you mean by legacy GL ?

JoeCFD

@SGaist legacy GL is the lib OPENGL_gl_LIBRARY: /usr/lib/x86_64-linux-gnu/libGL.so

and GLVND libraries for OpenGL and GLX:
OPENGL_opengl_LIBRARY: /usr/lib/x86_64-linux-gnu/libOpenGL.so
OPENGL_glx_LIBRARY: /usr/lib/x86_64-linux-gnu/libGLX.so

I would like to know the differences. I used Qt installer and therefore can not test the differences.

SGaist

There's no Legacy GL.

libGL is the official OpenGL implementation

GLX is the OpenGL library that talks with X11

GLVND is a vendor neutral GL dispatch library

JoeCFD

@SGaist what is /usr/lib/x86_64-linux-gnu/libOpenGL.so?

JoeCFD

@JoeCFD these messages

legacy GL is the lib OPENGL_gl_LIBRARY: /usr/lib/x86_64-linux-gnu/libGL.so
and GLVND libraries for OpenGL and GLX:
OPENGL_opengl_LIBRARY: /usr/lib/x86_64-linux-gnu/libOpenGL.so
OPENGL_glx_LIBRARY: /usr/lib/x86_64-linux-gnu/libGLX.so

are output from cmake

JoeCFD

@JoeCFD said in legacy GL vs GLVND Open GL:

libOpenGL

In addition, there's a new library, libOpenGL.so. It's basically the same as libGL.so, except that it only exports the OpenGL functions, not GLX. It also doesn't depend on libGLX, so it could also be used with an EGL or GLX application. The hope is that future applications will link against libOpenGL.so and either libGLX.so or libEGL.so. This makes for a cleaner separation of OpenGL from the window system binding. But, libGL.so will be kept around indefinitely for backwards compatibility.

from https://forums.gentoo.org/viewtopic-t-1117500-start-25.html

JoeCFD

The problem with the current situation is that different implementations of libGL.so.1 export a different set of functions, with no real rule or pattern between them.

There's nothing we can do about libGL.so.1 itself anymore. Too many buggy applications depend on that, and the chance of getting all of those applications fixed is zero.

The point of libOpenGL.so is to provide a clean separation between the window-system functions (GLX and EGL) and the OpenGL functions. In addition, since we don't have any compatibility baggage, the export list can be simple and well-defined. Unlike libGL.so, we can ensure that libOpenGL.so keeps the same export list forever.

https://github.com/NVIDIA/libglvnd/issues/63

JoeCFD

libOpenGL.so has not replaced libGL.so. But cmake claims libGL.so is legacy.

SGaist

Ok, I understand better the legacy concept in this case.