# png Android linking problem
**URL:** https://discourse.vtk.org/t/png-android-linking-problem/1311
**Category:** Development
**Created:** [July 9, 2019, 11:46am UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311 "2019-07-09T11:46:42Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@hcwiley](https://discourse.vtk.org/u/hcwiley)
#### Post date: [July 9, 2019, 11:46am UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311/1 "2019-07-09T11:46:43Z")
There is a bug with linking to `vtkpng` after compiling for arm64-v8a with Android NDK 18b. I’m linking against vtk-8.2.0 arm64-v8a with another project that uses NEON and has flags specifying that. The linking error is:
```
undefined reference to `png_init_filter_functions_neon'
```
I suggest looking at how OpenCV is handling their 3rd party lib png: requirements:
```
if(ENABLE_NEON)
list(APPEND lib_srcs arm/arm_init.c arm/filter_neon.S arm/filter_neon_intrinsics.c)
add_definitions(-DPNG_ARM_NEON_OPT=2)
elseif(AARCH64)
add_definitions(-DPNG_ARM_NEON_OPT=0) # NEON assembler is not supported
endif()
```
[See repo here](https://github.com/opencv/opencv/blob/bdaab1cee59d20916fb659fa37186af9e39da076/3rdparty/libpng/CMakeLists.txt#L31)
Not sure the VTK way to go about changing `vtkpng` to adopt some of these Android specific NEON changes. @ken-martin thoughts?
Just to get my problems sorted out I put `add_definitions(-DPNG_ARM_NEON_OPT=0)` at the top `vtkpng/CMakeLists.txt`. After doing that and recompiling VTK my linker error with the other project goes away.
---
### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [July 9, 2019, 1:26pm UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311/2 "2019-07-09T13:26:13Z")
We patch our PNG import to disable all optimization bits (our copies tend to be bare-bones and minimal for ease of porting the build system). We have `ThirdParty/png/vtkpng/pngpriv.h:#define PNG_ARM_NEON_OPT 0`. Is there a reason this isn’t working for you? It does work on our Android dashboard AFAICT: [https://open.cdash.org/buildSummary.php?buildid=5996639](https://open.cdash.org/buildSummary.php?buildid=5996639)
---
### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [July 9, 2019, 1:30pm UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311/3 "2019-07-09T13:30:29Z")
Oh, I see the `8.2.0` now. It is certainly possible that such a thing is missing on the `release-8.2` branch.
---
### Author:  [@hcwiley](https://discourse.vtk.org/u/hcwiley)
#### Post date: [July 10, 2019, 5:58am UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311/4 "2019-07-10T05:58:01Z")
It’s also not a build problem, it builds just fine on my machine as well. It only presents itself when being linked against by another Android project.
I’ll see about updating my [Android example](https://github.com/Scandy-co/AndroidVTK) to show you.
---
### Author:  [@Harry\_Potter](https://discourse.vtk.org/u/Harry_Potter)
#### Post date: [March 24, 2020, 5:09am UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311/5 "2020-03-24T05:09:49Z")
I cannot build vtk on the jetson nano for the issue. VTK-8.2.0-release
Any way to repair it?
---
### Author:  [@mwestphal](https://discourse.vtk.org/u/mwestphal)
#### Post date: [March 24, 2020, 5:15am UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311/6 "2020-03-24T05:15:58Z")
Please do not post image of code.
>
[http://idownvotedbecau.se/imageofcode](http://idownvotedbecau.se/imageofcode)
---
### Author:  [@ben.boeckel](https://discourse.vtk.org/u/ben.boeckel)
#### Post date: [March 24, 2020, 11:44am UTC](https://discourse.vtk.org/t/png-android-linking-problem/1311/7 "2020-03-24T11:44:26Z")
This was fixed on `master`, but I don’t think it made it onto the 8.2 release branch. Here’s the diff you need: [https://gitlab.kitware.com/vtk/vtk/-/merge\_requests/5603/diffs](https://gitlab.kitware.com/vtk/vtk/-/merge_requests/5603/diffs)