[FindGzOgreNext] Support Ogre 3.x and beyond

[oysstu]

The ogre-next project has released the next major version (v3.0.0 Eris). It seems that from now on, the project will follow a more conventional semver strategy, where new development is focused on the next major version.

Currently the FindGzOgre2 is hard-coded to find ogre-next releases with major version 2.x.x. It would probably be a good idea to generalize this to FindGzOgreNext. The "USE_NEW_PROJECT_NAME" feature was merged in v2.3.3, so support for v2.3.2 and earlier should probably be left to the existing FindGzOgre2 or dropped completely.

[j-rivero]

Wow these are good news! The FindGzOgreNext needs a good cleanup and we should try to use plain CMake modules from upstream. I can happily review code changes for this. Thanks @oysstu !

[oysstu]

I had a quick look at the ogre-next cmake setup, and it looks like they're not using modern cmake packaging conventions yet. Ideally, they would export the targets and components in a package config in ../share/cmake/. Instead, there's pkg-config files tied together by a big FindOGRE.cmake module in ../lib/../OGRE-Next/cmake.

The way I see it there's two possibilities

• Make the current FindGzOgre functionality work for 3.0.0+. E.g., remove hard checks for version 2 and rename OGRE2 variables to OGRE_NEXT. Remove workarounds for the old-style project layout, if any (e.g. before the move to 'Next').
• Try to rework FindGzOgreNext around the upstream FindOGRE.cmake module instead of utilizing the pkgconfig files directly

The upstream FindOGRE module has been around for a long time though, so I'm sure there's a reason the latter hasn't been done before.

[iche033]

when I wrote the original version using pkg-config many years ago I remember it's because the upstream find ogre module would not always find the correct ogre version or the right ogre plugin libraries. With the new ogre-next name change, things may be different. I think it's a good idea to use the upstream module instead of custom pkg-config code.

[oysstu]

I've created an issue in ogre-next (OGRECave/ogre-next#470). Their FindOGRE file still doesn't work well when both ogre-next and ogre is installed. Pkgconfig on the other hand behaves the same even if ogre is installed alongside ogre-next.

I.e., the following prints the same variable definitions even if ogre is installed.

cmake_minimum_required(VERSION 3.22)
project(ogre-test)

find_package(PkgConfig REQUIRED)
pkg_check_modules(OGRE_NEXT OGRE-Next REQUIRED)
pkg_check_modules(OGRE_NEXT_HLMS OGRE-Next-Hlms REQUIRED)
pkg_check_modules(OGRE_NEXT_OVERLAY OGRE-Next-Overlay REQUIRED)

get_cmake_property(_variableNames VARIABLES)
list (SORT _variableNames)
foreach (_variableName ${_variableNames})
    message(STATUS "${_variableName}=${${_variableName}}")
endforeach()

Also, the pkgconfig files are installed in a standard location, whereas the FindOGRE.cmake install location is non-standard.