This project is a simple proof of concept that shows you how to hijack Discord's internal game overlay from an external process without modifying any Discord files, loading any Discord modules, or hooking anything.

Discord's whitelisted internal module (DiscordHook64.dll), which is loaded by games using SetWindowHookEx, simply copies the framebuffer from a memory-mapped file. The code snippet from this repo is pretty much self-explanatory:

typedef struct _Header
{
	UINT Magic;
	UINT FrameCount;
	UINT NoClue;
	UINT Width;
	UINT Height;
	BYTE Buffer[1]; // B8G8R8A8
} Header;

bool ConnectToProcess(ConnectedProcessInfo& processInfo)
{
	std::string mappedFilename = "DiscordOverlay_Framebuffer_Memory_" + std::to_string(processInfo.ProcessId);
	processInfo.File = OpenFileMappingA(FILE_MAP_ALL_ACCESS, false, mappedFilename.c_str());
	if (!processInfo.File || processInfo.File == INVALID_HANDLE_VALUE)
		return false;

	processInfo.MappedAddress = static_cast<Header*>(MapViewOfFile(processInfo.File, FILE_MAP_ALL_ACCESS, 0, 0, 0));
	return processInfo.MappedAddress;
}

Please note that this straightforward example uses very basic CPU rendering, which does not offer optimal performance. In addition, regardless of your intention to use GPU rendering (such as DirectX), the framebuffer will still be copied by the CPU.

Video showing the example (in case embed does not work click here)

Image showing the example

Image showing custom project that renders using DX11

Image showing custom project rendering over anticheat protected game