seperate window manager backend from imgui frontend

this allows for different backends to be used for imgui with ease.

src/frontend/CMakeLists.txt

@@ -41,30 +41,25 @@ add_library(imgui
     ${imgui_SOURCE_DIR}/imgui_demo.cpp
 )
 
-target_include_directories(imgui PUBLIC ${imgui_SOURCE_DIR}/ ${imgui_SOURCE_DIR}/backends)
-
-# the backend we want
-find_package(SDL2 CONFIG REQUIRED)
-target_sources(imgui PRIVATE ${imgui_SOURCE_DIR}/backends/imgui_impl_sdl.cpp ${imgui_SOURCE_DIR}/backends/imgui_impl_sdlrenderer.cpp)
-target_link_libraries(imgui PRIVATE SDL2::SDL2)
+target_include_directories(imgui PUBLIC ${imgui_SOURCE_DIR})
 
 # memory editor
 add_library(imgui_club INTERFACE)
 target_include_directories(imgui INTERFACE ${imgui_club_SOURCE_DIR}/imgui_memory_editor)
 # fetch imgui is done!
 
+# always include backend after fetching imgui
+add_subdirectory(backend)
+
 add_executable(main
     main.cpp
     system.cpp
     debugger/io.cpp
 )
 
-find_package(SDL2 CONFIG REQUIRED)
-
 target_link_libraries(main PRIVATE GBA)
-target_link_libraries(main PRIVATE SDL2::SDL2)
-target_link_libraries(main PRIVATE SDL2::SDL2main)
 target_link_libraries(main PRIVATE imgui imgui_club)
+target_link_libraries(main PRIVATE backend)
 
 set(FOUND_MINIZIP FALSE)
 

src/frontend/backend/CMakeLists.txt

@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.20.0)
+
+add_subdirectory(sdl2)

src/frontend/backend/sdl2/CMakeLists.txt

@@ -0,0 +1,23 @@
+cmake_minimum_required(VERSION 3.20.0)
+
+add_library(backend
+    backend_sdl2.cpp
+    ${imgui_SOURCE_DIR}/backends/imgui_impl_sdl.cpp
+    ${imgui_SOURCE_DIR}/backends/imgui_impl_sdlrenderer.cpp
+)
+
+target_include_directories(backend PRIVATE
+    ${imgui_SOURCE_DIR}/backends
+)
+
+target_include_directories(backend PUBLIC
+    ${CMAKE_CURRENT_SOURCE_DIR}
+)
+
+find_package(SDL2 CONFIG REQUIRED)
+
+target_link_libraries(backend PRIVATE imgui)
+target_link_libraries(backend PRIVATE SDL2::SDL2)
+target_link_libraries(backend PRIVATE GBA)
+
+target_apply_lto_in_release(backend)