cmake: fix pkg-config handling

Avoid non-intentional call of "include(FindPkgConfig)"
It should be handled in the root CMakeLists.txt (safely for cross-compiling)

CMakeLists.txt

@@ -698,7 +698,7 @@ ocv_cmake_hook(POST_COMPILER_OPTIONS)
 # ----------------------------------------------------------------------------
 if(UNIX)
   if(NOT APPLE_FRAMEWORK OR OPENCV_ENABLE_PKG_CONFIG)
-    if(CMAKE_CROSSCOMPILING AND NOT DEFINED ENV{PKG_CONFIG_LIBDIR}
+    if(CMAKE_CROSSCOMPILING AND NOT DEFINED ENV{PKG_CONFIG_LIBDIR} AND NOT DEFINED ENV{PKG_CONFIG_SYSROOT_DIR}
         AND NOT OPENCV_ENABLE_PKG_CONFIG
     )
       if(NOT PkgConfig_FOUND)

cmake/OpenCVUtils.cmake

@@ -743,7 +743,7 @@ macro(ocv_check_modules define)
     endif()
     unset(${define}_${__modname}_FOUND)
   endforeach()
-  if(COMMAND pkg_check_modules)
+  if(PKG_CONFIG_FOUND OR PkgConfig_FOUND)
     pkg_check_modules(${define} ${ARGN})
   endif()
   if(${define}_FOUND)

modules/videoio/cmake/init.cmake

@@ -19,8 +19,6 @@ function(ocv_add_external_target name inc link def)
   endif()
 endfunction()
 
-include(FindPkgConfig)
-
 add_backend("ffmpeg" WITH_FFMPEG)
 add_backend("gstreamer" WITH_GSTREAMER)
 add_backend("v4l" WITH_V4L)

modules/videoio/cmake/plugin.cmake

-#=============================================
-# build with OpenCV
-include("${OpenCV_SOURCE_DIR}/cmake/OpenCVUtils.cmake")
-
 function(ocv_create_builtin_videoio_plugin name target videoio_src_file)
 
   ocv_debug_message("ocv_create_builtin_videoio_plugin(${ARGV})")
@@ -36,71 +32,3 @@ function(ocv_create_builtin_videoio_plugin name target videoio_src_file)
   add_dependencies(opencv_videoio_plugins ${name})
 
 endfunction()
-
-#=============================================
-# standalone build
-
-function(ocv_create_videoio_plugin default_name target target_desc videoio_src_file)
-
-  set(OPENCV_PLUGIN_NAME ${default_name} CACHE STRING "")
-  set(OPENCV_PLUGIN_DESTINATION "" CACHE PATH "")
-  project(${OPENCV_PLUGIN_NAME} LANGUAGES CXX)
-
-  set(BUILD_SHARED_LIBS ON CACHE BOOL "")
-  if(NOT BUILD_SHARED_LIBS)
-    message(FATAL_ERROR "Static plugin build does not make sense")
-  endif()
-
-  if(NOT OpenCV_SOURCE_DIR)
-    message(FATAL_ERROR "OpenCV_SOURCE_DIR must be set to build the plugin!")
-  endif()
-
-  include("${OpenCV_SOURCE_DIR}/modules/videoio/cmake/init.cmake")
-
-  if(NOT TARGET ${target})
-    message(FATAL_ERROR "${target_desc} was not found!")
-  endif()
-
-  set(modules_ROOT "${CMAKE_CURRENT_LIST_DIR}/../../..")
-  set(videoio_ROOT "${modules_ROOT}/videoio")
-  set(core_ROOT "${modules_ROOT}/core")
-  set(imgproc_ROOT "${modules_ROOT}/imgproc")
-  set(imgcodecs_ROOT "${modules_ROOT}/imgcodecs")
-
-  add_library(${OPENCV_PLUGIN_NAME} MODULE "${videoio_ROOT}/src/${videoio_src_file}")
-  target_include_directories(${OPENCV_PLUGIN_NAME} PRIVATE
-    "${CMAKE_CURRENT_BINARY_DIR}"
-    "${videoio_ROOT}/src"
-    "${videoio_ROOT}/include"
-    "${core_ROOT}/include"
-    "${imgproc_ROOT}/include"
-    "${imgcodecs_ROOT}/include"
-  )
-  target_compile_definitions(${OPENCV_PLUGIN_NAME} PRIVATE BUILD_PLUGIN)
-
-  # Fixes for build
-  target_compile_definitions(${OPENCV_PLUGIN_NAME} PRIVATE __OPENCV_BUILD)
-  file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/cvconfig.h" "#pragma once")
-  file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/cv_cpu_config.h" "#pragma once")
-  file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/opencv2/opencv_modules.hpp" "#pragma once")
-
-  target_link_libraries(${OPENCV_PLUGIN_NAME} PRIVATE ${target})
-  set_target_properties(${OPENCV_PLUGIN_NAME} PROPERTIES
-    CXX_STANDARD 11
-    CXX_VISIBILITY_PRESET hidden
-  )
-
-  # Hack for Windows
-  if(WIN32)
-    find_package(OpenCV REQUIRED core imgproc videoio)
-    target_link_libraries(${OPENCV_PLUGIN_NAME} ${OpenCV_LIBS})
-  endif()
-
-  if(OPENCV_PLUGIN_DESTINATION)
-    set_target_properties(${OPENCV_PLUGIN_NAME} PROPERTIES LIBRARY_OUTPUT_DIRECTORY "${OPENCV_PLUGIN_DESTINATION}")
-    message(STATUS "Output destination: ${OPENCV_PLUGIN_DESTINATION}")
-  endif()
-
-  message(STATUS "Library name: ${OPENCV_PLUGIN_NAME}")
-
-endfunction()

modules/videoio/cmake/plugin_standalone.cmake

+#=============================================
+# standalone build
+
+include(FindPkgConfig)
+
+#=============================================
+# build with OpenCV
+include("${OpenCV_SOURCE_DIR}/cmake/OpenCVUtils.cmake")
+
+function(ocv_create_videoio_plugin default_name target target_desc videoio_src_file)
+
+  set(OPENCV_PLUGIN_NAME ${default_name} CACHE STRING "")
+  set(OPENCV_PLUGIN_DESTINATION "" CACHE PATH "")
+  project(${OPENCV_PLUGIN_NAME} LANGUAGES CXX)
+
+  set(BUILD_SHARED_LIBS ON CACHE BOOL "")
+  if(NOT BUILD_SHARED_LIBS)
+    message(FATAL_ERROR "Static plugin build does not make sense")
+  endif()
+
+  if(NOT OpenCV_SOURCE_DIR)
+    message(FATAL_ERROR "OpenCV_SOURCE_DIR must be set to build the plugin!")
+  endif()
+
+  include("${OpenCV_SOURCE_DIR}/modules/videoio/cmake/init.cmake")
+
+  if(NOT TARGET ${target})
+    message(FATAL_ERROR "${target_desc} was not found!")
+  endif()
+
+  set(modules_ROOT "${CMAKE_CURRENT_LIST_DIR}/../../..")
+  set(videoio_ROOT "${modules_ROOT}/videoio")
+  set(core_ROOT "${modules_ROOT}/core")
+  set(imgproc_ROOT "${modules_ROOT}/imgproc")
+  set(imgcodecs_ROOT "${modules_ROOT}/imgcodecs")
+
+  add_library(${OPENCV_PLUGIN_NAME} MODULE "${videoio_ROOT}/src/${videoio_src_file}")
+  target_include_directories(${OPENCV_PLUGIN_NAME} PRIVATE
+    "${CMAKE_CURRENT_BINARY_DIR}"
+    "${videoio_ROOT}/src"
+    "${videoio_ROOT}/include"
+    "${core_ROOT}/include"
+    "${imgproc_ROOT}/include"
+    "${imgcodecs_ROOT}/include"
+  )
+  target_compile_definitions(${OPENCV_PLUGIN_NAME} PRIVATE BUILD_PLUGIN)
+
+  # Fixes for build
+  target_compile_definitions(${OPENCV_PLUGIN_NAME} PRIVATE __OPENCV_BUILD)
+  file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/cvconfig.h" "#pragma once")
+  file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/cv_cpu_config.h" "#pragma once")
+  file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/opencv2/opencv_modules.hpp" "#pragma once")
+
+  target_link_libraries(${OPENCV_PLUGIN_NAME} PRIVATE ${target})
+  set_target_properties(${OPENCV_PLUGIN_NAME} PROPERTIES
+    CXX_STANDARD 11
+    CXX_VISIBILITY_PRESET hidden
+  )
+
+  # Hack for Windows
+  if(WIN32)
+    find_package(OpenCV REQUIRED core imgproc videoio)
+    target_link_libraries(${OPENCV_PLUGIN_NAME} ${OpenCV_LIBS})
+  endif()
+
+  if(OPENCV_PLUGIN_DESTINATION)
+    set_target_properties(${OPENCV_PLUGIN_NAME} PROPERTIES LIBRARY_OUTPUT_DIRECTORY "${OPENCV_PLUGIN_DESTINATION}")
+    message(STATUS "Output destination: ${OPENCV_PLUGIN_DESTINATION}")
+  endif()
+
+  message(STATUS "Library name: ${OPENCV_PLUGIN_NAME}")
+
+endfunction()

modules/videoio/misc/plugin_ffmpeg/CMakeLists.txt

@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 3.5)
 set(OpenCV_SOURCE_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../..")
 set(WITH_FFMPEG ON)
 set(OPENCV_FFMPEG_SKIP_BUILD_CHECK ON)
-include("${OpenCV_SOURCE_DIR}/modules/videoio/cmake/plugin.cmake")
+include("${OpenCV_SOURCE_DIR}/modules/videoio/cmake/plugin_standalone.cmake")
 ocv_create_videoio_plugin("opencv_videoio_ffmpeg" "ocv.3rdparty.ffmpeg" "FFmpeg" "cap_ffmpeg.cpp")
 
 message(STATUS "FFMPEG_libavcodec_VERSION=${FFMPEG_libavcodec_VERSION}")

modules/videoio/misc/plugin_gstreamer/CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.5)
 
 set(OpenCV_SOURCE_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../..")
 set(WITH_GSTREAMER ON)
-include("${OpenCV_SOURCE_DIR}/modules/videoio/cmake/plugin.cmake")
+include("${OpenCV_SOURCE_DIR}/modules/videoio/cmake/plugin_standalone.cmake")
 ocv_create_videoio_plugin("opencv_videoio_gstreamer" "ocv.3rdparty.gstreamer" "GStreamer" "cap_gstreamer.cpp")
 
 message(STATUS "Using GStreamer: ${GSTREAMER_VERSION}")