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jakesee

OpenGL Understanding OpenGL ... again

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Hi,

I have been playing with opengl for a 2 years now. So far, I have been using the following files:

gl.h, glu.h, opengl32.lib, glu.lib

I read a bunch of articles on opengl.org and some other places but still don't fully understand how to get the lastest opengl. Hope someone can verify what I know (pertaining to windows for a start):

1. Windows never updates gl.h (but why would the others do so?)
2. New features in later versions of opengl are declared in glext.h i.e. this file keeps growing bigger.
3. glext.h contains all declarations of every single vendor's routine for every opengl specification.
4. opengl32.lib /opengl32.dll is the combined compiled binary of glext.h and gl.h
5. glew.h/glew.lib provides the functions to determine if a specific glext function is available on the current host/GPU.
6. glee is just a less popular glew?
7. when a routine in opengl32.dll is run, it loads and runs the graphics card's driver.dll which will always be the latest opengl.
8. hence, wglCreateContext() always creates the lastest context?

I am sure I didn't quite get that right.. please correct me. Thanks.

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I'm not up to date with latest GL so I want to share my opinions to have a double check with other users as well. Take this with some salt.
Quote:
Original post by jakesee
1. Windows never updates gl.h (but why would the others do so?)
You must think this question in reverse. A good OS will sooner or later get its gl.h updated as this is the right way to do things. Windows does not update it because it considers GL a legacy API to be deprecated. This is awful, but D3D is fairly good and they'll use all the ways they can to get you into it.
Quote:
Original post by jakesee
2. New features in later versions of opengl are declared in glext.h i.e. this file keeps growing bigger.
Correct. It will never get smaller as this would break something (which is likely already broken anyway). So much for 15+ year compatibility.
This is probably GL's biggest drawback. Old stuff never really goes away.
Quote:
Original post by jakesee
3. glext.h contains all declarations of every single vendor's routine for every opengl specification.
Not quite. Most of the time, the routine you're looking for "is there" but sometimes you might have to declare your own pointers.
Quote:
Original post by jakesee
4. opengl32.lib /opengl32.dll is the combined compiled binary of glext.h and gl.h
No. Not in general at least. Just update your glext.h and this statement becomes false. This is probably partially true out of the box. The question is a bit odd as header files don't have to produce code - I am unsure right now if GL's headers would produce code, I think not. The DLL is likely to contain fairly more stuff, at least to implement all the functions which are only "declared" as function pointers in glext.h.

I cannot tell about {5} and {6}.

Quote:
Original post by jakesee
7. when a routine in opengl32.dll is run, it loads and runs the graphics card's driver.dll which will always be the latest opengl.
More or less. Let's say yes by cutting some corners.
Quote:
Original post by jakesee
8. hence, wglCreateContext() always creates the lastest context?
Sort of. It will create the best context it can figure out, but its logic is defined in WGL's static lib so for example you cannot have antialiasing. This is why you need stuff as WGL_ARB_create_context, WGL_ARB_create_context_profile, WGL_ARB_create_context_robustness...

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To make it short: Yes. You'll have to rip your ass and study WTF is going on with the "last" version of OpenGL when you just installed XP/Vista/7.

But hey! Millions of Linux users would be willing to pay you big bucks for your effort. So it's worth it as a way of saving money for your retirement.

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@Krohm
Thanks for the explainations and confirmations.

There's still one issue, regarding whether Windows should update gl.h.

General impression I gather is that Microsoft is to blame for not updating gl.h. However, if the opengl standard is to provide additional functionality through "extensions" in the glext.h, why would there be a need to update gl.h? That's what I don't understand.

Any reason why they wouldn't name the gl according to version number?


// gl.h (provided by OS)
#pragma comment("lib", "opengl32.lib") // lastest lib provided by OS
...

// gl2.h (download from opengl.org repository)
#include <gl/gl.h>
...

// gl3.h (download from opengl.org repository)
#include <gl/gl2.h>
...

// etc..

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The OGL headers are declarations, not definitions. Whether gl.h contains declarations for version 1.0 or 4.0 is immaterial as once new extensions are available you'll have to either make the additional declarations yourself or download a newer header. IIRC opengl32.dll (and the accompanying .lib) contain Microsoft's software implementation of OGL 1.1 (and most likely all the wiggle stuff). The actual hardware accelerated implementation will be provided by the gfx vendor's driver. This is why you need to query extensions to ensure that your vendor provides an implementation for whatever features you desire.

I think you're getting the header declarations that come bundled with MS's compilers (gl.h) with the actual implementation of whatever version of OGL is supported by the gfx vendor. Why don't MS update the headers? Well, for starters they back their own propriety gfx API but also because there's an existing repository for such things @ opengl.org, as well as various extension management libs (GLEE, GLEW, etc.)

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Quote:
Original post by jakesee
Hi,

I have been playing with opengl for a 2 years now. So far, I have been using the following files:

gl.h, glu.h, opengl32.lib, glu.lib

I read a bunch of articles on opengl.org and some other places but still don't fully understand how to get the lastest opengl. Hope someone can verify what I know (pertaining to windows for a start):

1. Windows never updates gl.h (but why would the others do so?)
2. New features in later versions of opengl are declared in glext.h i.e. this file keeps growing bigger.
3. glext.h contains all declarations of every single vendor's routine for every opengl specification.
4. opengl32.lib /opengl32.dll is the combined compiled binary of glext.h and gl.h
5. glew.h/glew.lib provides the functions to determine if a specific glext function is available on the current host/GPU.
6. glee is just a less popular glew?
7. when a routine in opengl32.dll is run, it loads and runs the graphics card's driver.dll which will always be the latest opengl.
8. hence, wglCreateContext() always creates the lastest context?

I am sure I didn't quite get that right.. please correct me. Thanks.


All that is explained in the Wiki at www.opengl.org/wiki
but I'll make clarifications.

1. yes, that's correct, but it doesn't matter. The ARB gives us glext.h and these days they give us gl3.h

3. glext.h also contains new core GL functions. These are not extensions.

4. no. they have nothing to do with glext.h
opengl32.dll comes with Windows and is almost never changed. I believe it offers GL 1.4 with Vista and 7 but this doesn't matter. It doesn't matter because it is not a true device driver. The true device driver would be ati...dll or nvogl....dll or intelGFX.....dll
which opengl32.dll loads automatically.

5. yes
6. Perhaps. I use glew because I prefer to call glewInit(). I don't like GLEE's automatic shit.

7. Yup, you get GL 2.1
WGL_ARB_create_context is for making GL 3.0, 3.1, 3.2, etc.

8. For simplicity, let's say yes

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