Merge pull request #401 from hongjiang-ye/master

Fix build error in windows by preventing duplicated DLL copies

Author: JoeyDeVries

CMakeLists.txt

@@ -252,7 +252,7 @@ function(create_project_from_sources chapter demo)
         if(WIN32)
             # configure_file(${SHADER} "test")
             add_custom_command(TARGET ${NAME} PRE_BUILD COMMAND ${CMAKE_COMMAND} -E copy ${SHADER} $<TARGET_FILE_DIR:${NAME}>)
-			add_custom_command(TARGET ${NAME} PRE_BUILD COMMAND ${CMAKE_COMMAND} -E copy ${DLLS} $<TARGET_FILE_DIR:${NAME}>)
+			add_custom_command(TARGET ${NAME} PRE_BUILD COMMAND ${CMAKE_COMMAND} -E copy_if_different ${DLLS} $<TARGET_FILE_DIR:${NAME}>)
         elseif(UNIX AND NOT APPLE)
             file(COPY ${SHADER} DESTINATION ${CMAKE_SOURCE_DIR}/bin/${chapter})
         elseif(APPLE)