samples: update parallel_backend examples

- use find_package(TBB)

samples/cpp/CMakeLists.txt

@@ -72,6 +72,8 @@ include("tutorial_code/calib3d/real_time_pose_estimation/CMakeLists.txt" OPTIONA
 if(OpenCV_FOUND AND NOT CMAKE_VERSION VERSION_LESS "3.1")
   add_subdirectory("example_cmake")
 endif()
-if(OpenCV_FOUND AND NOT CMAKE_VERSION VERSION_LESS "3.9")
+if(OpenCV_FOUND AND NOT CMAKE_VERSION VERSION_LESS "3.9"
+    AND NOT OPENCV_EXAMPLES_SKIP_PARALLEL_BACKEND
+)
   add_subdirectory("tutorial_code/core/parallel_backend")
 endif()

samples/cpp/tutorial_code/core/parallel_backend/CMakeLists.txt

@@ -2,25 +2,36 @@ cmake_minimum_required(VERSION 3.9)
 
 find_package(OpenCV REQUIRED COMPONENTS opencv_core)
 
-find_package(OpenMP)
-if(OpenMP_FOUND)
-  project(opencv_example_openmp_backend)
-  add_executable(opencv_example_openmp_backend example-openmp.cpp)
-  target_link_libraries(opencv_example_openmp_backend PRIVATE
-      opencv_core
-      OpenMP::OpenMP_CXX
-  )
+if(NOT OPENCV_EXAMPLES_SKIP_PARALLEL_BACKEND_OPENMP
+    AND NOT OPENCV_EXAMPLES_SKIP_OPENMP
+)
+  find_package(OpenMP)
+  if(OpenMP_FOUND)
+    project(opencv_example_openmp_backend)
+    add_executable(opencv_example_openmp_backend example-openmp.cpp)
+    target_link_libraries(opencv_example_openmp_backend PRIVATE
+        opencv_core
+        OpenMP::OpenMP_CXX
+    )
+  endif()
 endif()
 
-# TODO: find_package(TBB)
-find_path(TBB_INCLUDE_DIR NAMES "tbb/tbb.h")
-find_library(TBB_LIBRARY NAMES "tbb")
-if(TBB_INCLUDE_DIR AND TBB_LIBRARY AND NOT OPENCV_EXAMPLE_SKIP_TBB)
-  project(opencv_example_tbb_backend)
-  add_executable(opencv_example_tbb_backend example-tbb.cpp)
-  target_include_directories(opencv_example_tbb_backend SYSTEM PRIVATE ${TBB_INCLUDE_DIR})
-  target_link_libraries(opencv_example_tbb_backend PRIVATE
-      opencv_core
-      ${TBB_LIBRARY}
-  )
+if(NOT OPENCV_EXAMPLES_SKIP_PARALLEL_BACKEND_TBB
+    AND NOT OPENCV_EXAMPLES_SKIP_TBB
+    AND NOT OPENCV_EXAMPLE_SKIP_TBB  # deprecated (to be removed in OpenCV 5.0)
+)
+  find_package(TBB)
+  if(NOT TBB_FOUND)
+    find_path(TBB_INCLUDE_DIR NAMES "tbb/tbb.h")
+    find_library(TBB_LIBRARY NAMES "tbb")
+  endif()
+  if(TBB_INCLUDE_DIR AND TBB_LIBRARY)
+    project(opencv_example_tbb_backend)
+    add_executable(opencv_example_tbb_backend example-tbb.cpp)
+    target_include_directories(opencv_example_tbb_backend SYSTEM PRIVATE ${TBB_INCLUDE_DIR})
+    target_link_libraries(opencv_example_tbb_backend PRIVATE
+        opencv_core
+        ${TBB_LIBRARY}
+    )
+  endif()
 endif()