Don't trigger find_package when user builds a shared-lib version of SDL3

[Sand3r-]

Currently when user builds SDL_shadercross along with a shared-library version of SDL3, the check if(NOT TARGET SDL3::SDL3-static) in CMakeLists.txt won't block the package search with find_package because it only verifies if the target of a static version of SDL3 library is present. If user doesn't have SDL3 installed in the system, the build will fail resulting with:

CMake Warning at external/SDL_shadercross/CMakeLists.txt:26 (find_package):
  By not providing "FindSDL3.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "SDL3", but
  CMake did not find one.

  Could not find a package configuration file provided by "SDL3" (requested
  version 3.1.3) with any of the following names:

    SDL3Config.cmake
    sdl3-config.cmake

  Add the installation prefix of "SDL3" to CMAKE_PREFIX_PATH or set
  "SDL3_DIR" to a directory containing one of the above files.  If "SDL3"
  provides a separate development package or SDK, be sure it has been
  installed.

This PR extends the check to also cover for the SDL3 shared library case.

[madebr]

I'd rather do something smart as we do in SDL_image.

If SDLSHADERCROSS_SHARED is true, then the SDL3::SDL3-shared target must be available (SDL3-shared component)
If SDLSHADERCROSS_STATIC is true, then the SDL3::Headers target must be available (Headers component)

[Sand3r-]

Updated

[madebr]

We're getting closer :)

SDL_shadercross' CMakeLists.txt is also different from that from SDL_image: SDL_image supports building only a single library: shared or static (not both). SDL_shadercross can build both a shared and static library.

So you need to keep the current if(BUILD_SHARED_LIBS) set(SDLSHADERCROSS_(SHARED|STATIC)_DEFAULT ) if/else,
then do these options

option(SDLSHADERCROSS_SHARED "Build shared SDL_shadercross library" ${SDLSHADERCROSS_SHARED_DEFAULT})
option(SDLSHADERCROSS_STATIC "Build static SDL_shadercross library" ${SDLSHADERCROSS_STATIC_DEFAULT})

And after these variables are correctly initialized can you calculate what targets/components you need, and call find_package.

[Sand3r-]

Thanks for the suggestion. I have moved the condition to be present after the options and it now checks for the appropriate targets depending on whether SDLSHADERCROSS_SHARED or SDLSHADERCROSS_STATIC are set to ON before running find_package.

[madebr]

@Sand3r- Can you check your use case with my change?

Note to maintainers: this PR should be merged with "Squash and merge"