Use Eigen from Hunter

Fix issue https://github.com/ruslo/hunter/issues/192

Author: ruslo

cmake/OpenCVFindLibsPerf.cmake

@@ -34,11 +34,21 @@ endif(WITH_CUDA)
 
 # --- Eigen ---
 if(WITH_EIGEN)
-  find_path(EIGEN_INCLUDE_PATH "Eigen/Core"
-            PATHS /usr/local /opt /usr $ENV{EIGEN_ROOT}/include ENV ProgramFiles ENV ProgramW6432
-            PATH_SUFFIXES include/eigen3 include/eigen2 Eigen/include/eigen3 Eigen/include/eigen2
-            DOC "The path to Eigen3/Eigen2 headers"
-            CMAKE_FIND_ROOT_PATH_BOTH)
+  if(HUNTER_ENABLED)
+    hunter_add_package(Eigen)
+    find_package(Eigen REQUIRED)
+    get_target_property(
+        EIGEN_INCLUDE_PATH
+        Eigen::eigen
+        INTERFACE_INCLUDE_DIRECTORIES
+    )
+  else()
+    find_path(EIGEN_INCLUDE_PATH "Eigen/Core"
+              PATHS /usr/local /opt /usr $ENV{EIGEN_ROOT}/include ENV ProgramFiles ENV ProgramW6432
+              PATH_SUFFIXES include/eigen3 include/eigen2 Eigen/include/eigen3 Eigen/include/eigen2
+              DOC "The path to Eigen3/Eigen2 headers"
+              CMAKE_FIND_ROOT_PATH_BOTH)
+  endif()
 
   if(EIGEN_INCLUDE_PATH)
     ocv_include_directories(${EIGEN_INCLUDE_PATH})