Cross Compiling VTK for Mobile Architectures

[agirault (Alexis Girault)]

@timt

Modern CMake has a lot of nice built-in functionality for cross compiling for these architectures now. It would be great if we could simply rely on CMake to handle all of this, and delete the toolchain and iOS- and Android-specific CMake files from the VTK source.

+1 on dumping the custom CMake toolchains in VTK and using the native CMake support instead. Obviously a lot easier to maintain, and more scalable when needing to configure more CMake properties than the ones currently hardcoded. Some useful links:

• https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling-for-ios-tvos-or-watchos
• https://cmake.org/cmake/help/latest/prop_tgt/FRAMEWORK.html

I don’t know anything about the Android build, but it looks like there was support even before: https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling-for-android

@timt

However, at first pass CMake has an issue with finding a valid threading library

Those tickets might help with dependency issues on iOS:

• FindThreads: https://gitlab.kitware.com/cmake/cmake/-/issues/18993#note_631486
• findPackage with CONFIG: https://gitlab.kitware.com/cmake/cmake/-/issues/19655#note_619698

@timt

Alexis and Julien have also noted interest around building VTK as an XCFramework, something of which I currently have little knowledge. This seems like the ideal end goal at present.

See this comment on the CMake’s issue tracker to follow on that topic:
https://gitlab.kitware.com/cmake/cmake/-/issues/21752#note_903018

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@ken-martin @ben.boeckel I thought VTK had an iOS job with tests on CDash but I can’t seem to find it. I haven’t done any vtk development for iOS in a while: has it been removed, or am I misremembering?