A port of the OmniScale algorithm from SameBoy to Godot 3+. Works similarly to hqx at arbitrary precision.
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.
From left to right: Nearest, Bilinear, OmniScale