cmake: unpack protobuf into binary directory

modules/dnn/3rdparty/protobuf/CMakeLists.txt

@@ -41,7 +41,7 @@ function(append_if_exist OUTPUT_LIST)
     set(${OUTPUT_LIST} ${${OUTPUT_LIST}} PARENT_SCOPE)
 endfunction()
 
-set(PROTOBUF_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/sources/protobuf-3.1.0)
+set(PROTOBUF_ROOT "${PROTOBUF_CPP_PATH}/protobuf-3.1.0")
 
 if(MSVC)
   set(ATOMICOPS_INTERNALS ${PROTOBUF_ROOT}/src/google/protobuf/stubs/atomicops_internals_x86_msvc.cc)

modules/dnn/cmake/OpenCVFindLibProtobuf.cmake

@@ -30,7 +30,7 @@ else()
   include(${CMAKE_CURRENT_LIST_DIR}/download_protobuf.cmake)
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/protobuf)
   set(PROTOBUF_LIBRARIES libprotobuf)
-  set(PROTOBUF_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/protobuf/sources/protobuf-3.1.0/src)
+  set(PROTOBUF_INCLUDE_DIR ${PROTOBUF_CPP_PATH}/protobuf-3.1.0/src)
 endif()
 
 if(NOT UPDATE_PROTO_FILES)

modules/dnn/cmake/download_protobuf.cmake

@@ -1,6 +1,6 @@
 set(PROTOBUF_CPP_NAME "libprotobuf")
 set(PROTOBUF_CPP_DOWNLOAD_HASH "bd5e3eed635a8d32e2b99658633815ef")
-set(PROTOBUF_CPP_PATH "${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/protobuf/sources") # /protobuf-3.1.0 subdirectory
+set(PROTOBUF_CPP_PATH "${CMAKE_CURRENT_BINARY_DIR}/3rdparty/protobuf/sources") # /protobuf-3.1.0 subdirectory
 
 set(OPENCV_PROTOBUF_CPP_DOWNLOAD_URL ${OPENCV_PROTOBUF_URL};$ENV{OPENCV_PROTOBUF_URL};https://github.com/google/protobuf/releases/download/)