Use OpenCV functionality from within Unreal Engine

• Use cv::VideoCapture as an actor to get either camera or video images into a Render Target
• UCVUMat: UE-Managed wrapper for cv::UMat to allow implementation of algorithms in Blueprints
• Blueprint wrappers for image processing methods
• Conversion of UCVUMat to Render target and vice versa

If you want to use the functinality in your own project, you will need to

• Copy the Plugin from Plugins/OpenCV to your own project in the Plugins folder
• Edit your Build configuration to reference the OpenCV module, e.g. by adapting your Module.Build.cs similar to the following:

  PublicDependencyModuleNames.AddRange(new string[] { 
      "Core", "CoreUObject", "Engine", "InputCore", // These are default ones you probably already have
      "OpenCV" // <-- This is the important one ;)
  });
  
  PrivateIncludePaths.AddRange(
      new string[] {
         "OpenCV/Private", // Make the header files available so you can use OpenCV headers in your C++ code
      }
  );

Currently only Windows is supported. This is mainly limited by my (non-existent) understanding of how building and including with external libraries works on different platforms.

Tested on Windows, Unreal Engine 4.21
However, other versions might still work.

Q: I'm getting weird errors when including opencv header files.

You might be getting compile time errors such as

1>F:\projects\UE4_Demo\Plugins\OpenCV\ThirdParty\opencv\include\opencv2/imgproc/imgproc_c.h(505): error C4190: 'cvReadChainPoint' has C-linkage specified, but returns UDT 'CvPoint' which is incompatible with C
1>  F:\projects\UE4_Demo\Plugins\OpenCV\ThirdParty\opencv\include\opencv2/core/types_c.h(866): note: see declaration of 'CvPoint'

I could not yet figure out what exactly is causing this, but it usually it helps to move the opencv includes "up" in the include order, i.e. including them as early as possible. Unfortunately that means sometimes it is necessary to include them in a header file even if OpenCV is used only in the implementation.