COMP: update findOpenCV.cmake for openCV 4

CMake/FindOpenCV.cmake

@@ -28,11 +28,11 @@ if(OpenCV_DIR)
   if(OPENCV_SEARCH_PATH)
     find_path(
       opencv_INCLUDE_DIR
-      opencv/cv.h
+      opencv2/opencv.hpp
       PATHS "${OPENCV_SEARCH_PATH}"
       #no additional paths are added to the search if OpenCV_DIR
       NO_DEFAULT_PATH
-      PATH_SUFFIXES "include"
+      PATH_SUFFIXES "include" "include/opencv4"
       DOC "The directory where opencv/cv.h is installed")
   endif()
 endif()
@@ -40,17 +40,12 @@ endif()
 if(NOT opencv_INCLUDE_DIR)
   find_path(
     opencv_INCLUDE_DIR
-    opencv/cv.h
+    opencv2/opencv.hpp
     PATHS "${OpenCV_DIR}"
-    PATH_SUFFIXES "include"
+    PATH_SUFFIXES "include" "include/opencv4"
     DOC "The directory where opencv/cv.h is installed")
 endif()
 
-if(NOT EXISTS ${opencv_INCLUDE_DIR}/opencv2/opencv.hpp)
-  message(FATAL_ERROR "${opencv_INCLUDE_DIR}/opencv2/opencv.hpp does not exists. "
-    "Make sure you have opencv 2.3 or higher. We had searched in ${OPENCV_SEARCH_PATHS}")
-endif()
-
 set(opencv_core_NAMES opencv_core)
 set(opencv_ml_NAMES opencv_ml)
 
@@ -61,7 +56,7 @@ if (opencv_INCLUDE_DIR)
   if(NOT OpenCV_VERSION)
     file(READ "${opencv_INCLUDE_DIR}/opencv2/core/version.hpp" _header_content)
 
-    # detect the type of version file (2.3.x , 2.4.x or 3.x)
+    # detect the type of version file (2.3.x , 2.4.x, 3.x or 4.x)
     string(REGEX MATCH  ".*# *define +CV_VERSION_EPOCH +([0-9]+).*" has_epoch ${_header_content})
     string(REGEX MATCH  ".*# *define +CV_MAJOR_VERSION +([0-9]+).*" has_old_major ${_header_content})
     string(REGEX MATCH  ".*# *define +CV_MINOR_VERSION +([0-9]+).*" has_old_minor ${_header_content})