Make a library with cmake that use the SDL - c++

Question

I am trying to create a library on the top of SDL2. For the compilation I'm using cmake.
First I had this CMakeLists.txt for the library :
cmake_minimum_required(VERSION 3.10)
project(SquareEngine)
set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_CURRENT_SOURCE_DIR}/cmake/")
find_package(SDL2 REQUIRED)
find_package(SDL2_image REQUIRED)
include_directories(${SDL2_INCLUDE_DIRS})
include_directories(${SDL2_IMAGE_INCLUDE_DIRS})
set (SRCS Main.cpp
Rectangle.cpp
Scene.cpp
SquareEngine.cpp)
set (HEADERS Rectangle.hpp
Scene.hpp
SquareEngine.hpp
utils/Color.hpp
utils/Vector.hpp)
add_library(SquareEngine ${SRCS} ${HEADERS} ${SDL} ${SDL_SRC})
target_link_libraries(SquareEngine ${SDL2_LIBRARIES} ${SDL2_IMAGE_LIBRARIES})
To include the SDL2 and SDL2 image I follow this instructions.
When I try to build it's work perfectly.
Now I try to use my library in a project. I create my own project and I link my librairy that is located in a subfolder /SquareEngine in my project. For the project I use this CMakeLists.txt :
cmake_minimum_required(VERSION 3.10)
project(Demo)
set (SRCS Main.cpp)
add_subdirectory(SquareEngine)
add_executable(Demo ${SRCS})
target_link_libraries(Demo PUBLIC SquareEngine)
target_include_directories(Demo PUBLIC SquareEngine)
When I try to build the project I got an error like this :
Cannot open include file: 'SDL.h': No such file or directory
I try to figure out for long time and I don't have any clue why.
Maybe it will be better to use the SDL in static rather than shared ?

Answer 1

I think you need to add the SDL include dirs to the SquareEngine library:
target_include_directories(SquareEngine PUBLIC ${SDL2_INCLUDE_DIRS} ${SDL2_IMAGE_INCLUDE_DIRS})

Answer 2

The most recent SDL2 releases provide SDL2::* CMake targets such that you don't need to fiddle with CMake variables anymore.
So there's no more need to ship your custom FindSDL2.cmake and/or FindSDL2_image.cmake modules.
With those, you can rewrite your cmake script as:
cmake_minimum_required(VERSION 3.10)
project(SquareEngine)
find_package(SDL2 REQUIRED CONFIG)
find_package(SDL2_image REQUIRED CONFIG)
set (SRCS
Main.cpp
Rectangle.cpp
Scene.cpp
SquareEngine.cpp
)
set (HEADERS
Rectangle.hpp
Scene.hpp
SquareEngine.hpp
utils/Color.hpp
utils/Vector.hpp
)
add_library(SquareEngine ${SRCS} ${HEADERS})
target_link_libraries(SquareEngine PRIVATE SDL2::SDL2 SDL2_image::SDL2_image)
target_include_directories(SquareEngine
PUBLIC
$<TARGET_PROPERTY:SDL2::SDL2,INTERFACE_INCLUDE_DIRECTORIES>
$<TARGET_PROPERTY:SDL2_image::SDL2_image,INTERFACE_INCLUDE_DIRECTORIES>
"$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>"
)
It can then be used in your game as:
cmake_minimum_required(VERSION 3.10)
project(Demo)
set (SRCS Main.cpp)
add_subdirectory(SquareEngine)
add_executable(Demo ${SRCS})
target_link_libraries(Demo PUBLIC SquareEngine)