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GLEW Linker Error/Check Extension Support at Compile Time?


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#1 Geometrian   Crossbones+   -  Reputation: 1601

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Posted 27 June 2013 - 03:59 AM

Hi,

 

I am trying to compile and run some of my new code on my old laptop. My current code was developed on a GL 4-capable machine, and uses several key extensions that are not supported on the older device.

 

When building on the newer machine, it works perfectly. When building on the older machine, despite a nearly identical build chain, it fails with linker errors. Specifically, some GLEW functions are referenced as undefined. I am linking against the library, in the same place as the working build, and, incidentally, last in the linker order. The undefined functions include __glewUniform1D and __glewBindImageTextureEXT. Such functions come from extensions (in those cases, GL_ARB_gpu_shader_fp64 and GL_ARB_shader_image_load_store, repsectively)--notably extensions that the older laptop doesn't list as supported.

 

I have an extremely fuzzy conception of how GLEW actually works, but since other GLEW functions (e.g. glewInit) are not listed as undefined, I draw the conclusion that perhaps the extensions don't exist and so can't be linked to. Though, since the library versions of GLEW are the same (1.5) and I can't think of a mechanism besides, I can't be sure.

 

However, it also gives rise to another idea. Since the extensions aren't supported anyway, it would be convenient to be able to remove code that won't work at compile time. Though, since GPU detection, I expect, can only be done at runtime, I don't see how that could work.

 

So: why the linker errors? And, can extensions be checked at compile-time?

 

Thanks,

-G


And a Unix user said rm -rf *.* and all was null and void...|There's no place like 127.0.0.1|The Application "Programmer" has unexpectedly quit. An error of type A.M. has occurred.

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#2 BitMaster   Crossbones+   -  Reputation: 4427

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Posted 27 June 2013 - 05:32 AM

It's unclear to me why you have linker errors. The point of GLEW is that it retrieves the extension support of the system it's currently running on - the capabilities of the system it was originally compiled on should not matter at all. You should investigate what "nearly identical build chain" means, especially the part 'nearly'. 
 
Considering that GLEW 1.5 is more than five years old, you might want to investigate a newer version, even if you do not need support for newer extensions.
 
Also take a close look at how you built GLEW for both platforms.
 
If you are linking GLEW statically, doublecheck that GLEW_STATIC is defined everywhere where GLEW is included.

Are there any warnings apart from the errors?

#3 Geometrian   Crossbones+   -  Reputation: 1601

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Posted 27 June 2013 - 10:05 PM

It's unclear to me why you have linker errors. The point of GLEW is that it retrieves the extension support of the system it's currently running on - the capabilities of the system it was originally compiled on should not matter at all. You should investigate what "nearly identical build chain" means, especially the part 'nearly'.

I mean, insomuch as they can be on different computers and OSes (Ubuntu 10.04 versus 12.04). The sources are the same, the cmake files are the same, except for one flag which just changes where it finds my libraries.
 

Considering that GLEW 1.5 is more than five years old, you might want to investigate a newer version, even if you do not need support for newer extensions.

I think I was mistaken when I said the GLEW versions are the same. They are both the latest available for their respective platforms, but that's 1.5 versus 1.6.
 

Also take a close look at how you built GLEW for both platforms.

Good plan.
 

If you are linking GLEW statically, doublecheck that GLEW_STATIC is defined everywhere where GLEW is included.

I am, they are.
 

Are there any warnings apart from the errors?

No.

I believe the problem was due to the GLEW version. I updating the older OS to 13.04, and got the newer version of GLEW the linker errors disappeared.

Thanks,


And a Unix user said rm -rf *.* and all was null and void...|There's no place like 127.0.0.1|The Application "Programmer" has unexpectedly quit. An error of type A.M. has occurred.




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