Cmake find_package() fix and runtime path

[rotolof]

• The first commit will install FindCUDNN.cmake alongside DarknetConfig.cmake, fixes Including darknet library in my project using cmake #4729.

  Without this, the CMake command:

  find_package(Darknet)

  will not work because CMake doesn't know how to find CUDNN.

• The second commit will install the library libdarknet.so and binaries uselib and darknet into subdirectories of CMAKE_INSTALL_PREFIX and set the runtime paths accordingly.

  Without this, if you specified, for example, -DCMAKE_INSTALL_PREFIX=/usr/local that stuff was still installed in the build directory.

[cenit]

about the second commit, while i can understand that in principle it would be the best default, in practice darknet has the legacy of producing build artifacts in the source root folder.
If you want to customize it, you need to pass -DINSTALL_LIB_DIR=/path/to/your/favourite/lib/dir
and -DINSTALL_BIN_DIR=/path/to/your/favourite/bin/dir

[cenit]

for the first commit, i agree with it and i might accept it
at the moment the copy is performed by build.ps1, in this way it would be done by cmake itself

[rotolof]

about the second commit, while i can understand that in principle it would be the best default, in practice darknet has the legacy of producing build artifacts in the source root folder.
If you want to customize it, you need to pass -DINSTALL_LIB_DIR=/path/to/your/favourite/lib/dir
and -DINSTALL_BIN_DIR=/path/to/your/favourite/bin/dir

I see, I was wondering if there was a reason for not doing that already. For me it's OK as long as I'm able to specify the installation path.
I'm reverting those changes but the runtime path still needs to be set otherwise uselib and darknet will not find darknet.so unless they are in the same directory.

[cenit]

ok thanks.
Can you please put the RPATH variable in CACHE too?
Also, please take care of the copy of all cmake modules that we distribute in this repo, so that downstream projects like yours, which do not use build.ps1 script, can benefit from them

[rotolof]

ok thanks.
Can you please put the RPATH variable in CACHE too?

Done!

Also, please take care of the copy of all cmake modules that we distribute in this repo, so that downstream projects like yours, which do not use build.ps1 script, can benefit from them

At the moment it wouldn't be useful as FindStb and FindPThreads4W are not called in DarknetConfig.cmake. Maybe there's something wrong with the logic in DarknetConfig.cmake but I don't know the project well enough to tell.

If I'm not mistaken, Stb is embedded in the project and it's only used for building so it's not really a dependency, and Threads are searched with other modules?

[cenit]

while you're right for Stb, this is not true for PThreads4W. But see #8303 for an open issue about that, which you just reminded me of having to take a decision

[rotolof]

Ok, I added FindPThreads4W.cmake