Re-add optional OIDN denoise as an external dynamic library.

[bruvzg]

Implements godotengine/godot-proposals#7640

Alternative variant #82832 (uses executable).

Pros: more stable API, no writing/reading to disk.
Cons: library should be the same architecture as executable (and there's no ARM64 prebuild library for macOS in official releases), might have issues with dependency loading paths.

TODO: ensure correct library lookup paths are set on all platforms.

[akien-mga]

Superseded by #82832.

[atirut-w]

Bummer. Using OIDN as an external lib sounded mor reasonable for integrations.

[akien-mga]

Well this can be reconsidered later if need be, it doesn't change much in the implementation. But not having macOS ARM support would be the bigger bummer IMO.

[bruvzg]

But not having macOS ARM support would be the bigger bummer IMO.

It seems to be possible to build it for ARM macOS, but for some reason it's not part of official releases.

[atafra]

We're planning to include ARM macOS builds for OIDN starting with the next major release.

[bruvzg]

TODO: ensure correct library lookup paths are set on all platforms.

Seems like on Windows, OIDN is unusable as a dynamic library unless all dependency libs are in the same folder as executable.

Main dll is loading fine, and it's finding module dll, but unable to load its dependencies (tbb dlls), and since it's using LoadLibraryW we can't override library search path with AddDllDirectory on the engine side.

But in should be fixable in the OIDN module loader with something like this:

diff --git a/core/module.cpp b/core/module.cpp
index 14ac590..db74014 100644
--- a/core/module.cpp
+++ b/core/module.cpp
@@ -50,7 +50,7 @@ OIDN_NAMESPACE_BEGIN
     // Prevent the system from displaying a message box when the module fails to load
     UINT prevErrorMode = GetErrorMode();
     SetErrorMode(prevErrorMode | SEM_FAILCRITICALERRORS);
-    void* module = LoadLibraryW(path.c_str());
+    void* module = LoadLibraryExW(path.c_str(), nullptr, LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
     SetErrorMode(prevErrorMode);
   #else
     void* module = dlopen(path.c_str(), RTLD_NOW | RTLD_LOCAL);

I'll check it on Linux and macOS a bit later.
Edit: macOS libs seems to have correctly set @rpath, so it's not an issue.
Edit: seems to be working on Linux as well, so it's a Windows specific issue.
Edit: upstream PR - RenderKit/oidn#179

[bruvzg]

A new PR version - #83314