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PredeX

OpenGL How portable is OpenGL?

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PredeX    122
Im playing with the thought of learning myself OGL, and I read that it is portable to other platforms. So now I''d like to know to what extend is OGL portable to other platforms? Are there any limitations, i.e. if you are a C programmer do you have to stick to the ANSI standard to keep it portable and stuff like that?? *PredeX*

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Null and Void    1088
quote:
Original post by PredeX
Are there any limitations, i.e. if you are a C programmer do you have to stick to the ANSI standard to keep it portable and stuff like that??


That''s portability of the language, not OpenGL.

quote:
Original post by PredeX
Im playing with the thought of learning myself OGL, and I read that it is portable to other platforms. So now I''d like to know to what extend is OGL portable to other platforms?


OpenGL is portable to many platforms including: Linux/BSD/Unixes, MacOS (old and new), Windows, BeOS, any many more (some not-so-officially). GLU should be supported by the same platforms. Now, WGL, GLX, and other such libraries aren''t 100% portable. Same with the Win32 API and XLib, they aren''t portable. To get around this you can use a library like SDL or GLUT.

[Resist Windows XP''s Invasive Production Activation Technology!]

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ANSI2000    122
It is portable on all the supported platforms. www.opengl.org should have a list.

What is portable about OpenGL. Take this example...

glPushMatrix();
glBegin(GL_TRIANGLE)
glVertex3f(2.0, 1.0, 7.0);
glVertex3f(5.0, 5.0, 7.0);
glVertex3f(3.0, 6.0, 7.0);
glEnd();
glPopMatrix();

The above calls are all OGL methods. If you where to take this snipet of code and paste within your Win32, Mac, Linux and other C compilers and press build it would compile. Of course you would have to setup you compiler to link the OGL libs for that platform. Also for different languages like mentioned Fortran, VB etc... The conventions will be different.

As for the base OS calls needed. You can either use GLU or code your own OS calls like: message loops, event handlers etc...

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Dactylos    122
quote:
Original post by ANSI2000
As for the base OS calls needed. You can either use GLU or code your own OS calls like: message loops, event handlers etc...


quote:

GLU sucks ... (from personal experience) ... write generic C code, then alter per platform as is necesary



I think you guys mean GLUT.

quote:

If you where to take this snipet of code and paste within your Win32, Mac, Linux and other C compilers and press build it would compile.

Actually it wouldn''t compile, since there is a semicolon missing and GL_TRIANGLE should be GL_TRIANGLES (I know, typos, I just had to point it out, sorry ).

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Shag    122
BUT SURELY ANY EXTRA LAYER ADDS OVERHEAD!

I''m just saying that in order to be compatible, refrain from using OS specific calls ... but do it internally in code!

Forget these libraries which claim to do it all ... in favour of performance

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Shag    122
ABSOLUTELY ... THAT'S MY POINT!!!!

We all accept that a good engine is written in assembly ... right?


NO ... with the right compilers it doesn't matter (much)

But by trying to include the overhead for each OS, you are not doing yourself a favour! Target your system for a specific sytem, then re-write the OS stuff!

Edited by - Shag on October 25, 2001 9:03:56 PM

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Null and Void    1088
quote:
Original post by Shag
NO ... with the right compilers it doesn't matter (much)


Exactly, which the right interoperability wrapper it doesn't matter (much). SDL is meant for games, you think they'll make it slow on purpose? I haven't noticed any loss of speed yet.

[Resist Windows XP's Invasive Production Activation Technology!]

Edited by - Null and Void on October 25, 2001 10:00:24 PM

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Dactylos    122
quote:
Original post by Shag
But by trying to include the overhead for each OS, you are not doing yourself a favour! Target your system for a specific sytem, then re-write the OS stuff!


Why include the overhead of OpenGL when you could write directly to the card? Target your game for a specific graphics card, then re-write the card specific stuff to support other graphics cards.

It''s all a matter of trade-offs.

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Guest Anonymous Poster   
Guest Anonymous Poster
quote:
Original post by Dactylos
Why include the overhead of OpenGL when you could write directly to the card? Target your game for a specific graphics card, then re-write the card specific stuff to support other graphics cards.

It''s all a matter of trade-offs.


But wouldnt that be much more work since theres a whole bunch of cards which are used by gamers??

Let''s say i want to program a game for Windows and Linux, could i use GCC (DJGPP) with OGL and just compile under both platforms(preferably) without any changes?

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brettporter    122
AP lacks the ability to understand sarcasm

But the answer to the question is yes an no. Once you have the rendering context, you can write code that won''t change OS to OS, but you will have to abstract GLX, WGL or AGL (are there any others now).

My library compiles under GCC (Cygwin - not DJGPP as thats DOS and OpenGL support would have to be through Mesa) for Windows and Linux. Programs that use it compile to Windows & Linux without changes.

There is -negligable overhead-. You are only making virtual function calls on OS specific stuff, not OGL stuff. Virtual functions aren''t so slow anyway out of inner loops, especially when it is only for resizing windows, etc that you don''t do often.

So, yes, OpenGL is portable. (Hey, is there really any competition anyway? What else can you use for 3D on Linux - DirectX via Wine?!


~~~
Cheers!
Brett Porter
PortaLib3D : A portable 3D game/demo libary for OpenGL
Community Service Announcement: Read How to ask questions the smart way before posting!

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