cmake: allow #include "SDL2/SDL.h.h" when using SDL2 as subproject

CMakeLists.txt

@@ -2988,7 +2988,7 @@ string(TOLOWER "${CMAKE_BUILD_TYPE}" lower_build_type)
 execute_process(COMMAND ${CMAKE_COMMAND} -E make_directory "${CMAKE_CURRENT_BINARY_DIR}/include-config-${lower_build_type}")
 # 3. generate SDL_config in an build_type-dependent folder (which should be first in the include search path)
 file(GENERATE
-    OUTPUT "${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL_config.h"
+    OUTPUT "${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL2/SDL_config.h"
     INPUT "${SDL2_BINARY_DIR}/SDL_config.h.intermediate")
 
 # Prepare the flags and remove duplicates
@@ -3039,9 +3039,9 @@ else()
 endif()
 
 configure_file("${SDL2_SOURCE_DIR}/include/SDL_revision.h.cmake"
-  "${SDL2_BINARY_DIR}/include/SDL_revision.h")
+  "${SDL2_BINARY_DIR}/include/SDL2/SDL_revision.h")
 
-# Copy all non-generated headers to "${SDL2_BINARY_DIR}/include"
+# Copy all non-generated headers to "${SDL2_BINARY_DIR}/include/SDL2"
 # This is done to avoid the inclusion of a pre-generated SDL_config.h
 file(GLOB SDL2_INCLUDE_FILES ${SDL2_SOURCE_DIR}/include/*.h)
 set(SDL2_COPIED_INCLUDE_FILES)
@@ -3050,7 +3050,7 @@ foreach(_hdr IN LISTS SDL2_INCLUDE_FILES)
     list(REMOVE_ITEM SDL2_INCLUDE_FILES "${_hdr}")
   else()
     get_filename_component(_name "${_hdr}" NAME)
-    set(_bin_hdr "${SDL2_BINARY_DIR}/include/${_name}")
+    set(_bin_hdr "${SDL2_BINARY_DIR}/include/SDL2/${_name}")
     list(APPEND SDL2_COPIED_INCLUDE_FILES "${_bin_hdr}")
     add_custom_command(OUTPUT "${_bin_hdr}"
         COMMAND ${CMAKE_COMMAND} -E copy_if_different "${_hdr}" "${_bin_hdr}"
@@ -3284,7 +3284,11 @@ if(NOT WINDOWS_STORE AND NOT SDL2_DISABLE_SDL2MAIN)
   add_dependencies(SDL2main sdl_headers_copy)
   # alias target for in-tree builds
   add_library(SDL2::SDL2main ALIAS SDL2main)
-  target_include_directories(SDL2main BEFORE PRIVATE "${SDL2_BINARY_DIR}/include" PRIVATE "${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>")
+  target_include_directories(SDL2main BEFORE
+    PRIVATE "${SDL2_BINARY_DIR}/include"
+    PRIVATE "${SDL2_BINARY_DIR}/include/SDL2"
+    PRIVATE "${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL2"
+  )
   target_include_directories(SDL2main PUBLIC "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include>" $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}> $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/SDL2>)
   if (WIN32)
     target_link_libraries(SDL2main PRIVATE shell32)
@@ -3375,7 +3379,8 @@ if(SDL_SHARED)
   target_link_libraries(SDL2 PRIVATE ${EXTRA_LIBS} ${EXTRA_LDFLAGS} ${EXTRA_LDFLAGS_BUILD} ${CMAKE_DEPENDS})
   target_include_directories(SDL2 PUBLIC
       "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include>"
-      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>>"
+      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include/SDL2>"
+      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL2>"
       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/SDL2>"
   )
@@ -3410,7 +3415,8 @@ if(SDL_STATIC)
   target_link_libraries(SDL2-static PRIVATE ${EXTRA_LIBS} ${EXTRA_LDFLAGS} ${CMAKE_DEPENDS})
   target_include_directories(SDL2-static PUBLIC
       "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include>"
-      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>>"
+      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include/SDL2>"
+      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL2>"
       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/SDL2>"
   )
@@ -3441,7 +3447,8 @@ if(SDL_TEST)
       EXPORT_NAME SDL2test)
   target_include_directories(SDL2_test PUBLIC
       "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include>"
-      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>>"
+      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include/SDL2>"
+      "$<BUILD_INTERFACE:${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL2>"
       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/SDL2>")
   target_link_libraries(SDL2_test PRIVATE ${EXTRA_TEST_LIBS})
@@ -3559,8 +3566,8 @@ if(NOT SDL2_DISABLE_INSTALL)
   install(
     FILES
       ${SDL2_INCLUDE_FILES}
-      "${SDL2_BINARY_DIR}/include/SDL_revision.h"
-      "${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL_config.h"
+      "${SDL2_BINARY_DIR}/include/SDL2/SDL_revision.h"
+      "${SDL2_BINARY_DIR}/include-config-$<LOWER_CASE:$<CONFIG>>/SDL2/SDL_config.h"
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/SDL2)
 
   string(TOUPPER "${CMAKE_BUILD_TYPE}" UPPER_BUILD_TYPE)