When do I need to use an OpenGL function loader?

Question

I\'m a bit confused about when exactly I need to use an OpenGL function loader like GLEW. In general, it seems like you first obtain a window and valid OpenGL context and th

Answer 1

datenwolf's answer is great, but I wanted to clarify something you said in the first bullet point of your question.

Core and extension status is not platform-dependent or even mutually exclusive.

Core means that some feature was introduced in a certain version of OpenGL. There are core functions, which are things that are guaranteed to exist in version X.Y and there are even core extensions, which are extensions that were introduced alongside version X.Y. Core extensions provide the same functions, types, enums, etc. as the core feature only in an extension form that does not require a specific version.

Framebuffer Objects went core in OpenGL 3.0, and are slightly less restrictive than the EXT extension (GL_EXT_framebuffer_object) that predates OpenGL 3.0. However, it is not necessary to have an OpenGL 3.0 implementation to have access to the core version of FBOs - an OpenGL 2.1 implementation might offer the core functionality.

In the extension specification for GL_ARB_framebuffer_object, you will find:

Issues

(8) Why don't the new tokens and entry points in this extension have "ARB" suffixes like other ARB extensions?

RESOLVED: Unlike most ARB extensions, this is a strict subset of functionality already approved in OpenGL 3.0. This extension exists only to support that functionality on older hardware that cannot implement a full OpenGL 3.0 driver. Since there are no possible behavior changes between the ARB extension and core features, source code compatibility is improved by not using suffixes on the extension.

That is the first mention of a core extension that I can recall, but it is not the last. Since then many ARB extensions have been created that "backport" (if you will) core functionality from a higher version.

Here is some sample output gathered by parsing gl.xml for another core extension:

 >> Command:  void glBufferStorage (GLenum target, GLsizeiptr size, const void *
                                    data, GLbitfield flags)

  * Provided by GL_ARB_buffer_storage (gl|glcore)

  * Core in                   GL_VERSION_4_4    (   gl 4.4)

It is core in 4.4 (guaranteed to exist in a 4.4 implementation), but because the extension that provides it is glcore, this core function may be available in older implementations if the core extension is available.

The simple piece of software I wrote to parse gl.xml for this information can be found here if you are interested.