Export dynamic and static library names in sdl2_image-config cmake input file

[bcarmo-caio]

I am opening this PR to export SDL2_image library names (whether it is dynamic or static) so end user may call them just using a variable as it done in SDL2

Currently, a CMakeFile.txt has to be like

...
target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES} SDL2_image::SDL2_image)
...

And with this fix, we can call it using

target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES} ${SDL2_IMAGE_LIBRARIES})
or
target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES} ${SDL2_IMAGE_STATIC_LIBRARIES})

I kept the same format as SDL2 so users may expect similar naming

---

P.S.: I don't why SDL2 exports the variables but does not use them inside sdl2-config.cmake itself. I mean, they

set(SDL2_LIBRARIES SDL2::SDL2)                                                   
set(SDL2_STATIC_LIBRARIES SDL2::SDL2-static)

but then

if(TARGET SDL2::SDL2-static AND NOT TARGET SDL2::SDL2)

instead of

if(TARGET ${SDL2_STATIC_LIBRARIES} AND NOT TARGET ${SDL2_LIBRARIES})

I did test both cases (dynamic and static) here and I could remove the hardcoded SDL2_image::SDL2_image and SDL2_image::SDL2_image-static from the entire file.

---

When using dynamic (target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES} ${SDL2_IMAGE_LIBRARIES})):

$readelf -d test
Dynamic section at offset 0x52d88 contains 32 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libSDL2-2.0.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libSDL2_image-2.0.so.0] <-- IMG_Load will be loaded from here
...
 0x000000000000001d (RUNPATH)            Library runpath: [/opt/SDL2-2.28.2/lib:/home/user/SDL2_image-2.6.3_fixed/lib]



$readelf -s test
Symbol table '.dynsym' contains 122 entries:
...
101: 0000000000000000     0 FUNC    GLOBAL DEFAULT  UND IMG_Load  <-- IMG_Load call is present in .dynsym, so code
                                                                      is not in this binary

When using static (target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES} ${SDL2_IMAGE_STATIC_LIBRARIES})):

$readelf -d test
Dynamic section at offset 0x78d88 contains 31 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)             Shared library: [libSDL2-2.0.so.0]
...
 0x000000000000001d (RUNPATH)            Library runpath: [/opt/SDL2-2.28.2/lib] <-- No SDL2_image will be searched



readelf -s test
Symbol table '.symtab' contains 3595 entries:
3262: 0000000000035fa0    89 FUNC    GLOBAL DEFAULT   14 IMG_Load <--- because IMG_Load code is here in binary =)

Please do let me know if I am doing something wrong in removing the hardcoded names

Best regards

[madebr]

I intentionally did not add cmake variables to the satellite libraries as those are "the old way", and easy to corrupt.
SDL2 has these variables for backwards compatibility.

I think it's nicer to use SDL2_image::SDL2_image then ${SDL2_IMAGE_LIBRARIES}. CMake variables don't add value.

[bcarmo-caio]

Oh! I see. Thanks for letting me know that it was an old fashioned way and that SDL2 has kept it just for backwards compatibility.
I'm changing my project CMakeLists.txt to
target_link_libraries(${PROJECT_NAME} SDL2::SDL2 SDL2_image::SDL2_image)
right now =)

Also closing this PR as it seems to make no sense then.

Regards

[madebr]

SDL3 will not provide any CMake variables, so now you're prepared 😉

[bcarmo-caio]

Nice! Thanks for the heads up 👍

[madebr]

You might want to add SDL2_image::SDL2_image first.

target_link_libraries(${PROJECT_NAME} PRIVATE SDL2_image::SDL2_image SDL2::SDL2)

When SDL2_image is a static library, SDL2 symbols are required at link time.
SDL2_image::SDL2image does not automatically add SDL2::SDL2 so the user can choose between a shared/static SDL2 library, and also we don't know whether the SDL2::SDL2 target actually exists.