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I am learning now OpenGL and writing some geometrical abstractions over it for personal usage. I want my code to be maximally portable and I want to have GL context initialized in caller code (by means of FLTK, wxWidgets, WinAPI or any else supported platform).

I am reading now this popular article: https://learnopengl.com/Getting-started/Creating-a-window

Authors suggest there to use GLAD library, because this library provides creation of GL context (which does not fit me) and also it is used for 'retrieving addresses of functions' (quote: "Since there are many different versions of OpenGL drivers, the location of most of its functions is not known at compile-time and needs to be queried at run-time.").

My question is the following:

Does compiler really cannot get addresses of Opengl functions from GL-related .obj files which I specify in Linker Settings of Visual Studio? Do I really need to use wglGetProcAddress routine to refer to OpenGL functions? Is it possible to use OpenGL functions like any other functions from linked headers and .obj files?

Ivan P.
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1 Answers1

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Authors suggest there to use GLAD library, because this library provides creation of GL context (which does not fit me)

No, GLAD does not create or manage GL contexts in any way, and the website https://learnopengl.com/Getting-started/Creating-a-window never claims otherwise. They use GLFW for context and window management.

Does compiler really cannot get addresses of Opengl functions from GL-related .obj files which I specify in Linker Settings of Visual Studio?

No.

First of all, you do not specify OpenGL-related .obj files for the linker, but on Windows, you might use opengl32.lib, which is the import library file for opengl32.dll which comes with every windows version since Windows 95.

However, this DLL does not contain the OpenGL implementation you are typically using, but it contains Microsoft's OpenGL 1.1 GDI software rasterizer. The actual OpenGL implementation on windows is provided by an Installable Client Driver (ICD) which comes with your graphics driver. For OpenGL 1.0 and 1.1 functions, opengl32.dll will act as a trampoline and will forward the calls to the actual ICD DLL.

If you want to call any OpenGL function beyond OpenGL 1.1 (and that one is from 1997), you have to use the OpenGL extension mechanism in every case, as opengl32.dll does not provide these entry points at all, and the compiler/linker will of course not find them.

genpfault
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derhass
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    In simple words, GLAD manages function pointers for OpenGL. It is useful becuase OpenGL is only really a standard/specification it is up to the driver manufacturer to implement the specification to a driver that the specific graphics card supports. Since there are many different versions of OpenGL drivers, the location of most of its functions is not known at compile-time and needs to be queried at run-time. GLFW helps us at compile time only. – Avtar Sohi Oct 11 '21 at 12:51