# vtk9.4.0，vtk\_glad\_glBlitFramebuffer cant find Implementation
**URL:** https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941
**Category:** Support
**Created:** [December 2, 2024, 3:23am UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941 "2024-12-02T03:23:52Z")
**Posts on this page:** 15
**Page:** 1
### Author:  [@zist8888](https://discourse.vtk.org/u/zist8888)
#### Post date: [December 2, 2024, 3:23am UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/1 "2024-12-02T03:23:52Z")
I download vtk9.4.0 source,when compiled openxr project demo,show some error,that cant link.
read source,this define as this:
#define glad\_glBlitFramebuffer vtk\_glad\_glBlitFramebuffer
but i cant find vtk\_glad\_glBlitFramebuffer Implementation.someone can give suggestion.
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### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 3, 2024, 10:33pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/2 "2024-12-03T22:33:59Z")
Hello,
Can you, please, redirect the output messages during VTK build to a text file and share it here?
best,
PC
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [December 3, 2024, 11:06pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/3 "2024-12-03T23:06:34Z")
> [@zist8888](#):
>
> show some error,that cant link.
Can you share the error messages?
Have you linked your demo to `VTK::glad` or `VTK::RenderingOpenGL2` atleast?
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### Author:  [@zist8888](https://discourse.vtk.org/u/zist8888)
#### Post date: [December 4, 2024, 10:06am UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/4 "2024-12-04T10:06:29Z")
I have been compiled vtk9.4.0 that not error,contain vtkglad library. my demo dont directly use glad,which is openxr project. vtk9.3.0 is good,now compile it failed. some error as :
vtkXRInterfaceHelper.obj : error LNK2001: **unresolved external symbol** vtk\_glad\_glBlitFramebuffer
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### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 4, 2024, 1:46pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/5 "2024-12-04T13:46:28Z")
That’s a linker error. It means a library was not found or doesn’t have the mentioned symbol. That error could be the last of long chain of errors that may have started long before that. The best practice in solving unclear building errors is to look for the very first error that showed up during VTK’s lengthy build. Hence, I have to insist: Can you, please, redirect the output messages during VTK build to a text file and share it here? Without the full log it is very difficult to diagnose the problem.
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### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [December 4, 2024, 1:52pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/6 "2024-12-04T13:52:54Z")
`LNK2001` is a typical Visual Studio error.
Please, refer to this: [visual studio - What is the default location for MSBuild logs? - Stack Overflow](https://stackoverflow.com/questions/11526552/what-is-the-default-location-for-msbuild-logs) on how to get a build log from MSBuild.
If you are using `nmake` or `cl` in a command line, just enter a `[your command line] > my_build_log.txt 2>&1`. This command will redirect the output (both regular and errors) to a file called `my_build_log.txt` instead of printing them to the screen. That file can then be shared here for analysis.
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [December 4, 2024, 2:29pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/7 "2024-12-04T14:29:39Z")
> [@zist8888](#):
>
> vtkXRInterfaceHelper.obj : error LNK2001: **unresolved external symbol** vtk\_glad\_glBlitFramebuffer
Where is this `vtkXRInterfaceHelper.obj` object file coming from? There is no source file named `vtkXRInterfaceHelper.cxx` in VTK. As always, when you have linker errors, please read the entire build output and share it here so we can help you fix the issue 🙂
Is your project available on github or elsewhere, so that we can look at your build system files?
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### Author:  [@zist8888](https://discourse.vtk.org/u/zist8888)
#### Post date: [December 6, 2024, 9:18am UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/8 "2024-12-06T09:18:50Z")
thanks,vtkXRInterfaceHelper is my demo,not at github,I use Qt and compile type MSVC,dont show more error info.i read vtk source ,dont find vtk\_glad\_glBlitFramebuffer implementation,so i want to known reason.
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [December 6, 2024, 2:10pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/9 "2024-12-06T14:10:49Z")
> [@zist8888](#):
>
> .i read vtk source ,dont find vtk\_glad\_glBlitFramebuffer implementation,so i want to known reason.
It is in there. The linker error is because you most likely relied on indirect dependency linking? Can you share the compiler error?
`vtk_glad_glBlitFramebuffer` is the expanded result of the `glad_glBlitFramebuffer` symbol - [https://gitlab.kitware.com/vtk/vtk/-/blob/master/ThirdParty/glad/vtkglad/include/glad/vtk\_gl\_mangle.h#L790](https://gitlab.kitware.com/vtk/vtk/-/blob/master/ThirdParty/glad/vtkglad/include/glad/vtk_gl_mangle.h#L790) This is called mangling third party symbols. VTK does it so that the function doesn’t conflict with another glad library that could be used in an end user application.
`glad_glBlitFramebuffer` a function pointer, loaded at runtime by glad here [https://gitlab.kitware.com/vtk/vtk/-/blob/master/ThirdParty/glad/vtkglad/src/gl.c#L4225](https://gitlab.kitware.com/vtk/vtk/-/blob/master/ThirdParty/glad/vtkglad/src/gl.c#L4225)
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### Author:  [@zist8888](https://discourse.vtk.org/u/zist8888)
#### Post date: [December 9, 2024, 9:59am UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/10 "2024-12-09T09:59:49Z")
Thanks for your reply.I read my code again,find that glBlitFramebuffer be used in my project.when it was removed,compling is good.if i want to use glBlitFramebuffer ,shoud use which function to replace?
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [December 9, 2024, 2:00pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/11 "2024-12-09T14:00:24Z")
Include vtk’s glad header and then use it.
```cpp
#include
...
...
glBlitFramebuffer(....)
```
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### Author:  [@zist8888](https://discourse.vtk.org/u/zist8888)
#### Post date: [December 10, 2024, 12:51pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/12 "2024-12-10T12:51:39Z")
Add header #include\,error still exist.
#define glad\_glBlitFramebuffer vtk\_glad\_glBlitFramebuffer
this define is mean that i think glad\_glBlitFramebuffer is defined as vtk\_glad\_glBlitFramebuffer ,so vtk\_glad\_glBlitFramebuffer must be impleted?
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [December 10, 2024, 7:05pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/13 "2024-12-10T19:05:34Z")
> [@zist8888](#):
>
> this define is mean that i think glad\_glBlitFramebuffer is defined as vtk\_glad\_glBlitFramebuffer ,so vtk\_glad\_glBlitFramebuffer must be impleted?
That’s not how mangling works. The `glad_glBlitFramebuffer` is defined as `vtk_glad_glBlitFramebuffer ` so as to avoid calling an external `glad_glBlitFramebuffer`.
> [@zist8888](#):
>
> ,so vtk\_glad\_glBlitFramebuffer must be impleted?
As I said earlier, these are not declared as functions. They are function pointers that are initialized and assigned to function pointers from the OpenGL driver when glad is loaded.
Is your VTK 9.4.0 built as static or shared libraries?
Can you share project files privately, if not on github?
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### Author:  [@zist8888](https://discourse.vtk.org/u/zist8888)
#### Post date: [December 12, 2024, 6:27am UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/14 "2024-12-12T06:27:18Z")
shared libraries,you can use any code,and insert glBlitFramebuffer(0,0,0,0,0,0,0,0,0,0) in this code,then can try to complie it by MSVC.
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### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [January 1, 2025, 6:59pm UTC](https://discourse.vtk.org/t/vtk9-4-0-vtk-glad-glblitframebuffer-cant-find-implementation/14941/15 "2025-01-01T18:59:10Z")
Cannot reproduce. It works for me without issue even with shared VTK libraries. Please share project files, if possible.