Looking through the repo, some of the assembler [1] looks odd:

    getShdwOfst:
        xor bh,bh
        mov bl,al
        mov di,bx
        shl di,1
        shl di,1
        shl d1,1
        ...

Why shift one bit at a time, like you would on a CPU like the 6502 with no multi-bit shift instructions? Was this hand-ported from some system without those?

[1]: https://github.com/lanceewing/agi/blob/main/src/CMGRAPHX.ASM...