improve CMakeLists.txt

- upgrade CMake minimal version;
- define three options to give users more control over the build process;
- fix Win32 dynamic build by exporting useful functions;

CMakeLists.txt

@@ -1,34 +1,78 @@
-CMAKE_MINIMUM_REQUIRED(VERSION 2.6)
+CMAKE_MINIMUM_REQUIRED(VERSION 2.8.12)
+
+if(DEFINED PROJECT_NAME)
+    set(KCP_IS_TOP_PROJECT OFF)
+else()
+    set(KCP_IS_TOP_PROJECT ON)
+endif()
 
 project(kcp LANGUAGES C)
 
-include(CTest)
-include(GNUInstallDirs)
+cmake_policy(SET CMP0054 NEW)
 
-add_library(kcp STATIC ikcp.c)
-add_library(kcp_shared SHARED ikcp.c)
+option(KCP_BUILD_SHARED_LIBS "Build KCP as a shared lib" OFF)
+option(KCP_BUILD_INSTALL "Build install target" ${KCP_IS_TOP_PROJECT})
+option(KCP_BUILD_TESTS "Build tests" ${KCP_IS_TOP_PROJECT})
 
-set_property(TARGET kcp_shared PROPERTY LIBRARY_OUTPUT_NAME kcp)
+if(KCP_BUILD_SHARED_LIBS)
+    if(WIN32)
+        set(exports_def_file "${CMAKE_CURRENT_BINARY_DIR}/exports.def")
+        set(exports_def_contents
+"EXPORTS 
+    ikcp_create
+    ikcp_release
+    ikcp_setoutput
+    ikcp_recv
+    ikcp_send
+    ikcp_update
+    ikcp_check
+    ikcp_input
+    ikcp_flush
+    ikcp_peeksize
+    ikcp_setmtu
+    ikcp_wndsize
+    ikcp_waitsnd
+    ikcp_nodelay
+    ikcp_log
+    ikcp_allocator
+    ikcp_getconv
+")
 
-install(FILES ikcp.h DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+        file(WRITE "${exports_def_file}" "${exports_def_contents}")
+        add_library(kcp SHARED ikcp.h ikcp.c "${exports_def_file}")
+    else()
+        add_library(kcp SHARED ikcp.h ikcp.c)
+    endif()
+else()
+    add_library(kcp STATIC ikcp.h ikcp.c)
+endif()
 
-install(TARGETS kcp_shared
-    EXPORT kcp-targets
-    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-    INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
-)
+if(KCP_BUILD_INSTALL)
+    include(GNUInstallDirs)
 
-install(EXPORT kcp-targets
-    FILE kcp-config.cmake
-    NAMESPACE kcp::
-    DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/kcp
-)
+    set_target_properties(kcp PROPERTIES PUBLIC_HEADER ikcp.h)
 
-if (BUILD_TESTING)
+    install(TARGETS kcp
+        EXPORT kcp-targets
+        PUBLIC_HEADER DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
+        ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}"
+        LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}"
+        RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
+        INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+    )
+
+    install(EXPORT kcp-targets
+        FILE kcp-config.cmake
+        NAMESPACE kcp::
+        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/kcp
+    )
+endif()
+
+if(KCP_BUILD_TESTS)
     enable_language(CXX)
     
     add_executable(kcp_test test.cpp)
     if(MSVC AND NOT (MSVC_VERSION LESS 1900))
         target_compile_options(kcp_test PRIVATE /utf-8)
     endif()
-endif ()
+endif()