Image resize algorithm

What image resize algorithm is the internal standalne viewer using?
I prefer Spline36 or Bicubic for quality, NearestNeighbor for speed.
I'm glad if some algorithms such as above can be selectable.

It depends on the type of image being scaled, and (in some cases) the graphics driver or choices made by Windows.

It's usually bilinear.

Is it possible to specifically set the image resize algorithm? Because having no options at all makes it unusable.

Not currently.

Unusable in what sense? If you link your account and tell us more about the situations where you'd find changing the algorithm useful, and which algorithm(s) you want instead, and how/when Opus should decide to use them, we can consider it.

Because you say it's usually bilinear. Bilinear is not good. Lanczos gives better results.

Bilinear is not good enough even for video playback and they always include other algorithms, let alone using it for image resize.

No particular situation is targeted. I always avoid Bilinear.

FWIW, video playback doesn't go through our image resizing code. Video resizing is up to the codecs involved (e.g. ffdshow), and not something Opus itself controls.