Take advantage of IrrlichtMt target

[JosiahWI]

With the CMake changes to IrrlichtMt, it's now possible to use a target for IrrlichtMt.
Besides greatly improving the ease of setting up IrrlichtMt for users building the client, it removes the need for Minetest's CMake to include transitive dependencies such as image libraries and Android or iOS libs, cleaning it up a tiny bit. The PR works by finding the IrrlichtMt package and linking to the target it provides. If the package isn't found and it isn't building the client, it will still fall back to using just the headers of old Irrlicht or IrrlichtMt.

To do

Ready for Review

How to test

• Build and install IrrlichtMt, for example:
• cmake -S . -B build -DBUILD_SHARED_LIBS=OFF -DCMAKE_INSTALL_PREFIX=~/.local
• cmake --build build -j $(nproc)
• cmake --install build
• Build Minetest, for example:
• cmake -S . -B build -DRUN_IN_PLACE=TRUE -DCMAKE_PREFIX_PATH=~/.local
• cmake --build build -j $(nproc)
• Observe that it builds and runs correctly.
• Edit for documentation: CMAKE_INSTALL_PREFIX and CMAKE_PREFIX_PATH are only required if the installation is not wanted in the system paths. If left out, it will install with the other system libraries and will be found automatically.

[JosiahWI]

I don't know how this happened but I must have done something whacky with my branches, I'll fix it and force push.

[NeroBurner]

You'll need to update the wget URL with a precompiled binary package of the new IrrlichtMt repository, which provides the new IrrlichtMt::IrrlichtMt target

Or you change the wget command to download latest master and build it

[JosiahWI]

Where do I get that new URL/precompiled binary package?

[sfan5]

You'd get them when I tag IrrlichtMt 1.9.0mt2 and upload the binaries here.
But I don't want to do that until we know that it works (in case changes are needed).

So we're not stuck here, here's the same binaries of the current state uploaded in another place:

• http:https://minetest.kitsunemimi.pw/temp/ubuntu-bionic.tar.gz
• http:https://minetest.kitsunemimi.pw/temp/win32.zip
• http:https://minetest.kitsunemimi.pw/temp/win64.zip

[SmallJoker]

Is it still WIP or ready for re-review?

EDIT: clang 9 fails:

-- *** Will build version 5.5.0-dev-debug ***
CMake Error at CMakeLists.txt:65 (message):
-- Configuring incomplete, errors occurred!
  Irrlicht or IrrlichtMt headers are required to build the server, but none
See also "/home/runner/work/minetest/minetest/cmakebuild/CMakeFiles/CMakeOutput.log".
  found.

.. which indicated wrong behaviour, or is it in fact intended this way?

[JosiahWI]

I am not intending to add more functionality, but the Prometheus build uses old Irrlicht and I removed automatic header detection for old Irrlicht, which maybe I need to put back in? I was careful to support building the server with old irrlicht headers, but I required the variable to be set by hand.

Edit: To explain the problem simply, all clang 9 CI builds use the same build.sh script so I can't pass in a variable for Irrlicht headers to just the Prometheus build.

[JosiahWI]

Also MinGW is failing, and although I suspect the problem, it shouldn't be a problem, so this one requires me to check docs and do some research. I know this seems like it's moving really slowly; I'm working on it mostly on weekends so the bugs are being fixed at a very gradual pace.

[JosiahWI]

Something I hacked together in the Irrlicht CMake to save time added public dependencies unbeknownst to me (docs aren't even clear on the behavior) and its breaking the MinGW build. This will be on hold for a little bit until I work out the best solution and patch it.

[NeroBurner]

@JosiahWI I created a fix PR for the unintentional public dependencies minetest/irrlicht#39

Also added a branch using use_builtin_irrlicht_mt branch (PR for completeness #11276 ) in the CI

The resulting GitHub Actions show all builds green, except the MSVC ones because no 'GL/wglext.h' can be found

https://github.com/NeroBurner/minetest/runs/2862069811?check_suite_focus=true

[JosiahWI]

I will rebase shortly. Are the IrrlichtMt binaries for CI updated?

[JosiahWI]

I'm sorry, I did not see you had committed and I thought I had amended a commit or something. I will always check in the future so this won't happen again.

[JosiahWI]

Can you reapply the commit?
Edit: I put the lost changes back in.

[sfan5]

This works but I just thought of an edge case: If you build a server with IrrlichtMt available to cmake (not just the headers), you will get an executable that links to IrrlichtMt even though the library itself is not needed.

[NeroBurner]

https://stackoverflow.com/questions/58759647/how-to-get-include-directories-from-a-target-for-use-in-add-custom-target

We could use the following to get the include dir from the IrrlichtMt::IrrlichtMt target for the server executable

if(TARGET IrrlichtMt::IrrlichtMt)
    get_target_property(IRRLICHT_INCLUDE_DIR IrrlichtMt::IrrlichtMt INCLUDE_DIRECTORIES)
endif()

[JosiahWI]

We probably want the INTERFACE_INCLUDE_DIRECTORIES property if we do that. If a core dev would like the change to be done I can add it.

[sfan5]

sure.
Make sure to pull before committing, I added some changes yesterday.

[celeron55]

I'm giving this my +1, but if you don't mind making the irrlichtmt installation better guided within the error messages, it would be nice.

[sfan5]

You have IrrlichtMt installed system-wide

How it was before:

cmake .

How it is now:

cmake .

You have IrrlichtMt cloned to lib/irrlichtmt

(what end users probably do)

How it was before:

cmake .

How it is now:

cmake .

You have IrrlichtMt installed(!) in a folder

How it was before:

cmake -DIRRLICHT_INCLUDE_DIR=/somewhere/include -DIRRLICHT_LIBARY=/somewhere/lib/libIrrlichtMt.so .

How it is now:

cmake -DCMAKE_PREFIX_PATH=/somewhere .

You have IrrlichtMt cloned somewhere

(what developers probably do, including me)

How it was before:

cmake -DIRRLICHT_INCLUDE_DIR=/somewhere/include -DIRRLICHT_LIBARY=/somewhere/lib/Linux/libIrrlichtMt.a .

How it is now:

cmake -DCMAKE_PREFIX_PATH=/somewhere .