blitter has released a real-time dithering library for the Virtual Boy.
This is a column-based rendering library that uses a fast algorithm for real-time dithering using a predefined table of patterns.
It relies on drawing directly to the framebuffer using the movbsu instruction. As such, it does not run well on older/abandoned emulators such as Red Dragon or ViBE.
More information, downloads and discussion can be found in our forum in this thread.