cmake: cannot install SDL2_image when SDL2 is also built but not inst…

…alled

CMakeLists.txt

@@ -46,14 +46,20 @@ else()
     set(vendored_default OFF)
 endif()
 
+set(sdl2image_install_enableable ON)
+if ((TARGET SDL2 OR TARGET SDL2-static) AND SDL2_DISABLE_INSTALL)
+    # Cannot install SDL2_image when SDL2 is built in same built, and is not installed.
+    set(sdl2image_install_enableable OFF)
+endif()
+
 include(CMakeDependentOption)
 include(CMakePackageConfigHelpers)
 include(GNUInstallDirs)
 
 option(CMAKE_POSITION_INDEPENDENT_CODE "Build static libraries with -fPIC" ON)
 option(BUILD_SHARED_LIBS "Build the library as a shared library" ON)
 
-option(SDL2IMAGE_INSTALL "Enable SDL2_image install target" ${SDL2IMAGE_ROOTPROJECT})
+cmake_dependent_option(SDL2IMAGE_INSTALL "Enable SDL2_image install target" ${SDL2IMAGE_ROOTPROJECT} "${sdl2image_install_enableable}" OFF)
 option(SDL2IMAGE_DEPS_SHARED "Load dependencies dynamically" ON)
 option(SDL2IMAGE_VENDORED "Use vendored third-party libraries" ${vendored_default})