Add option to specify external directories for OpenCV

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "vendor/obs-ocr-deps"]
 	path = vendor/obs-ocr-deps
 	url = https://github.com/occ-ai/obs-ocr-deps.git
+[submodule "vendor/obs-backgroundremoval-dep-opencv"]
+	path = vendor/obs-backgroundremoval-dep-opencv
+	url = https://github.com/occ-ai/obs-backgroundremoval-dep-opencv.git

CMakeLists.txt

@@ -37,14 +37,30 @@ endif()
 set(USE_SYSTEM_OPENCV
     OFF
     CACHE STRING "Use system OpenCV")
-if(USE_SYSTEM_OPENCV)
-  if(OS_LINUX)
-    find_package(OpenCV REQUIRED COMPONENTS core imgproc dnn)
-    target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE "${OpenCV_LIBRARIES}")
-    target_include_directories(${CMAKE_PROJECT_NAME} SYSTEM PUBLIC "${OpenCV_INCLUDE_DIRS}")
-  else()
+
+set(BUILD_OPENCV_FROM_SOURCE
+    OFF
+    CACHE STRING "Build OpenCV from tarball")
+
+if(OS_LINUX)
+  if(USE_SYSTEM_OPENCV AND BUILD_OPENCV_FROM_SOURCE)
+    message(FATAL_ERROR "Only one of USE_SYSTEM_OPENCV and BUILD_OPENCV_FROM_SOURCE can be enabled!")
+  endif()
+else()
+  if(USE_SYSTEM_OPENCV)
     message(FATAL_ERROR "System OpenCV is only supported on Linux!")
+  elseif(BUILD_OPENCV_FROM_SOURCE)
+    message(FATAL_ERROR "Building OpenCV from source is only supported on Linux!")
   endif()
+endif()
+
+if(USE_SYSTEM_OPENCV)
+  find_package(OpenCV REQUIRED COMPONENTS core imgproc dnn)
+  target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE "${OpenCV_LIBRARIES}")
+  target_include_directories(${CMAKE_PROJECT_NAME} SYSTEM PUBLIC "${OpenCV_INCLUDE_DIRS}")
+elseif(BUILD_OPENCV_FROM_SOURCE)
+  include(cmake/BuildOpenCV.cmake)
+  target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE OpenCV)
 else()
   include(cmake/FetchOpenCV.cmake)
   target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE OpenCV)

cmake/BuildOpenCV.cmake

@@ -0,0 +1,36 @@
+include(FetchContent)
+
+set(OPENCV_SOURCE_URL
+    ""
+    CACHE STRING "URL of a Tesseract source tarball")
+
+set(OPENCV_SOURCE_HASH
+    ""
+    CACHE STRING "Hash of a Tesseract source tarball")
+
+FetchContent_Declare(
+  opencv_source
+  URL ${OPENCV_SOURCE_URL}
+  URL_HASH ${OPENCV_SOURCE_HASH})
+FetchContent_Populate(opencv_source)
+
+set(BUILD_OPENCV_BASEDIR ${CMAKE_BINARY_DIR}/build-opencv)
+
+set(BUILD_OPENCV_OUTPUTS
+    ${BUILD_OPENCV_BASEDIR}/release/${CMAKE_BUILD_TYPE}/lib/libopencv_imgproc.a
+    ${BUILD_OPENCV_BASEDIR}/release/${CMAKE_BUILD_TYPE}/lib/libopencv_core.a
+    ${BUILD_OPENCV_BASEDIR}/release/${CMAKE_BUILD_TYPE}/lib/opencv4/3rdparty/libzlib.a)
+
+set(BUILD_OPENCV_INCLUDE_DIR ${BUILD_OPENCV_BASEDIR}/release/${CMAKE_BUILD_TYPE}/include/opencv4)
+
+add_custom_command(
+  OUTPUT ${BUILD_OPENCV_OUTPUTS}
+  COMMAND ${CMAKE_SOURCE_DIR}/vendor/obs-backgroundremoval-dep-opencv/build-linux.sh ${CMAKE_BUILD_TYPE} main
+          ${opencv_source_SOURCE_DIR}
+  WORKING_DIRECTORY ${BUILD_OPENCV_BASEDIR})
+add_custom_target(build_opencv DEPENDS ${BUILD_OPENCV_OUTPUTS})
+
+add_library(OpenCV INTERFACE)
+add_dependencies(OpenCV build_opencv)
+target_link_libraries(OpenCV INTERFACE ${BUILD_OPENCV_OUTPUTS})
+target_include_directories(OpenCV SYSTEM INTERFACE ${BUILD_OPENCV_INCLUDE_DIR})