A port of the OmniScale algorithm from SameBoy to Godot 3+.
Works similarly to hqx at arbitrary precision.

Usage

Apply shader to a ShaderMaterial. Works best with unfiltered images and NO alpha blending (eg: ViewportTextures).
Screen-space shader mode untested, further experimentation may be required to work as a screen-space shader.

Screenshot

From left to right: Nearest, Bilinear, OmniScale