romopt asset packing

How romopt packs the cartridge

romopt uses deterministic stable first-fit decreasing, the bank-packing algorithm William B. Norris IV first used for cartridge layout in 1992.

1. Treat every LZSS stream, every independent 512-byte palette, and each shared font as an indivisible item. Nothing may straddle a 32 KiB LoROM bank.
2. Exclude bank $00; it is reserved for runtime code, constants, startup data, the SNES header, and vectors.
3. Sort items from largest to smallest. Equal sizes retain manifest order, then item-kind order, so identical inputs always produce identical packing.
4. For each item, scan banks from $01 upward and place it in the first bank whose remaining capacity is large enough. If none fits, open the next bank.
5. Give the chosen bank and slot to the linker. The visualization below is read back from the final linker map, so its addresses describe the emitted ROM rather than an estimate.

for item in stable_sort(items, key = (-bytes, manifest_order, kind)):
    bank = first bank where used[bank] + item.bytes <= 32768
    place(item, bank); used[bank] += item.bytes

Streams and palettes are separate because their far pointers are independent; small palettes can fill holes left by large streams. First-fit decreasing is a fast heuristic, not an exhaustive proof of the minimum possible bank count.