Use Windows SDK if DirectX SDK not installed

CMakeModules/FindWindowsSDK.cmake

@@ -501,6 +501,17 @@ IF(WINSDK_INCLUDE_DIR)
   IF(WINSDK_VERSION STREQUAL "7.1" AND (MSVC11 OR MSVC12 OR MSVC14))
     ADD_DEFINITIONS(-D_USING_V110_SDK71_)
   ENDIF()
+
+  IF(NOT DXSDK_DIR)
+    MESSAGE("Using DirectX from Windows SDK (${WINSDK_LIBRARY_DIRS})")
+    SET(DXSDK_DIR ${WINSDK_DIR})
+    FIND_LIBRARY(DXSDK_GUID_LIBRARY dxguid ${WINSDK_LIBRARY_DIRS})
+    FIND_LIBRARY(DXSDK_DINPUT_LIBRARY dinput8 ${WINSDK_LIBRARY_DIRS})
+    FIND_LIBRARY(DXSDK_DSOUND_LIBRARY dsound ${WINSDK_LIBRARY_DIRS})
+    FIND_LIBRARY(DXSDK_XAUDIO_LIBRARY xaudio2 ${WINSDK_LIBRARY_DIRS})
+    # TODO: FIND_LIBRARY(DXSDK_D3DX9_LIBRARY d3dx9)
+    FIND_LIBRARY(DXSDK_D3D9_LIBRARY d3d9 ${WINSDK_LIBRARY_DIRS})
+  ENDIF()
 ELSE()
   IF(NOT WindowsSDK_FIND_QUIETLY)
     MESSAGE(STATUS "Warning: Unable to find Windows SDK!")

CMakeModules/nel.cmake

@@ -1280,7 +1280,7 @@ MACRO(SETUP_EXTERNAL)
 
   IF(WIN32)
     # Must include DXSDK before WINSDK
-    FIND_PACKAGE(DirectXSDK REQUIRED)
+    FIND_PACKAGE(DirectXSDK)
     # IF(DXSDK_INCLUDE_DIR)
     #   INCLUDE_DIRECTORIES(${DXSDK_INCLUDE_DIR})
     # ENDIF()
@@ -1289,5 +1289,8 @@ MACRO(SETUP_EXTERNAL)
   IF(MSVC)
     FIND_PACKAGE(MSVC REQUIRED)
     FIND_PACKAGE(WindowsSDK REQUIRED)
+    IF(NOT DXSDK_DIR)
+      MESSAGE(FATAL_ERROR "DirectX SDK or DirectX files from Windows SDK not found.")
+    ENDIF()
   ENDIF()
 ENDMACRO()