Attached is an update to the original Prop Backpack TV overlay object, which allows users to define their own character glyphs (bitmaps). Unlike my initial attempt at this capacity, this version does not require mapping the entire font into RAM. Instead, 16-character blocks can be mapped, starting with $F0-$FF and working downwards. This is effected by placing the RAM blocks at the end of memory xxxx - $7FFF, so that they are contiguous with the ROM font, which begins at $8000. By changing the effective font address to the beginning of the RAM section and translating characters written into the overlay's window buffers by the amount of the offset, the font can bridge both RAM and ROM without exacting additional timing requirements on the realtime video overlay code.
Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. Antoine de Saint-Exupery