mirror of https://github.com/pret/pokecrystal.git
621 lines
14 KiB
Markdown
621 lines
14 KiB
Markdown
# Design Flaws
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These are parts of the code that do not work *incorrectly*, like [bugs and glitches](/docs/bugs_and_glitches.md), but that clearly exist just to work around a problem. In other words, with a slightly different design, the code would not need to exist at all. Design flaws may be exceptions to a usual rule, such as "tables of pointers in different banks use `dba`" ([one exception](#pic-banks-are-offset-by-pics_fix), [and another](#pokédex-entry-banks-are-derived-from-their-species-ids)) or "graphics used as a unit are stored and loaded contiguously" ([a notable exception](#footprints-are-split-into-top-and-bottom-halves)).
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## Contents
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- [Pic banks are offset by `PICS_FIX`](#pic-banks-are-offset-by-pics_fix)
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- [`PokemonPicPointers` and `UnownPicPointers` are assumed to start at the same address](#pokemonpicpointers-and-unownpicpointers-are-assumed-to-start-at-the-same-address)
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- [Footprints are split into top and bottom halves](#footprints-are-split-into-top-and-bottom-halves)
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- [`ITEM_C3` and `ITEM_DC` break up the continuous sequence of TM items](#item_c3-and-item_dc-break-up-the-continuous-sequence-of-tm-items)
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- [Pokédex entry banks are derived from their species IDs](#pokédex-entry-banks-are-derived-from-their-species-ids)
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- [Identical sine wave code and data is repeated five times](#identical-sine-wave-code-and-data-is-repeated-five-times)
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- [`GetForestTreeFrame` works, but it's still bad](#getforesttreeframe-works-but-its-still-bad)
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## Pic banks are offset by `PICS_FIX`
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[data/pokemon/pic_pointers.asm](/data/pokemon/pic_pointers.asm), [data/pokemon/unown_pic_pointers.asm](/data/pokemon/unown_pic_pointers.asm), and [data/trainers/pic_pointers.asm](/data/trainers/pic_pointers.asm) all have to use `dba_pic` instead of `dba`. This is a macro in [macros/data.asm](/macros/data.asm) that offsets banks by `PICS_FIX`:
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```asm
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dba_pic: MACRO ; dbw bank, address
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db BANK(\1) - PICS_FIX
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dw \1
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ENDM
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```
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The offset is translated into a correct bank by `FixPicBank` in [engine/gfx/load_pics.asm](/engine/gfx/load_pics.asm):
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```asm
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FixPicBank:
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; This is a thing for some reason.
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PICS_FIX EQU $36
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GLOBAL PICS_FIX
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push hl
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push bc
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sub BANK("Pics 1") - PICS_FIX
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ld c, a
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ld b, 0
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ld hl, .PicsBanks
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add hl, bc
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ld a, [hl]
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pop bc
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pop hl
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ret
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.PicsBanks:
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db BANK("Pics 1") ; BANK("Pics 1") + 0
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db BANK("Pics 2") ; BANK("Pics 1") + 1
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db BANK("Pics 3") ; BANK("Pics 1") + 2
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db BANK("Pics 4") ; BANK("Pics 1") + 3
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db BANK("Pics 5") ; BANK("Pics 1") + 4
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db BANK("Pics 6") ; BANK("Pics 1") + 5
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db BANK("Pics 7") ; BANK("Pics 1") + 6
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db BANK("Pics 8") ; BANK("Pics 1") + 7
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db BANK("Pics 9") ; BANK("Pics 1") + 8
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db BANK("Pics 10") ; BANK("Pics 1") + 9
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db BANK("Pics 11") ; BANK("Pics 1") + 10
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db BANK("Pics 12") ; BANK("Pics 1") + 11
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db BANK("Pics 13") ; BANK("Pics 1") + 12
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db BANK("Pics 14") ; BANK("Pics 1") + 13
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db BANK("Pics 15") ; BANK("Pics 1") + 14
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db BANK("Pics 16") ; BANK("Pics 1") + 15
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db BANK("Pics 17") ; BANK("Pics 1") + 16
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db BANK("Pics 18") ; BANK("Pics 1") + 17
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db BANK("Pics 19") ; BANK("Pics 1") + 18
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db BANK("Pics 20") ; BANK("Pics 1") + 19
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db BANK("Pics 21") ; BANK("Pics 1") + 20
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db BANK("Pics 22") ; BANK("Pics 1") + 21
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db BANK("Pics 23") ; BANK("Pics 1") + 22
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db BANK("Pics 24") ; BANK("Pics 1") + 23
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```
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**Fix:** Use `dba` instead of `dba_pic`, delete `FixPicBank`, and remove all four calls to `FixPicBank`.
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## `PokemonPicPointers` and `UnownPicPointers` are assumed to start at the same address
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In [gfx/pics.asm](/gfx/pics.asm):
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```asm
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; PokemonPicPointers and UnownPicPointers are assumed to start at the same
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; address, but in different banks. This is enforced in pokecrystal.link.
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SECTION "Pic Pointers", ROMX
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INCLUDE "data/pokemon/pic_pointers.asm"
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SECTION "Unown Pic Pointers", ROMX
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INCLUDE "data/pokemon/unown_pic_pointers.asm"
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```
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In [pokecrystal.link](/pokecrystal.link):
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```
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ROMX $48
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org $4000
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"Pic Pointers"
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"Pics 1"
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ROMX $49
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org $4000
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"Unown Pic Pointers"
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"Pics 2"
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```
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Two routines in [engine/gfx/load_pics.asm](/engine/gfx/load_pics.asm) make this assumption; `GetFrontpicPointer`:
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```asm
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ld a, [wCurPartySpecies]
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cp UNOWN
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jr z, .unown
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ld a, [wCurPartySpecies]
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ld d, BANK(PokemonPicPointers)
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jr .ok
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.unown
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ld a, [wUnownLetter]
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ld d, BANK(UnownPicPointers)
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.ok
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ld hl, PokemonPicPointers ; UnownPicPointers
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dec a
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ld bc, 6
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call AddNTimes
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```
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And `GetMonBackpic`:
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```asm
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; These are assumed to be at the same address in their respective banks.
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ld hl, PokemonPicPointers ; UnownPicPointers
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ld a, b
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ld d, BANK(PokemonPicPointers)
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cp UNOWN
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jr nz, .ok
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ld a, c
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ld d, BANK(UnownPicPointers)
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.ok
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dec a
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ld bc, 6
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call AddNTimes
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```
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**Fix:**
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Don't enforce `org $4000` in pokecrystal.link.
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Modify `GetFrontpicPointer`:
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```asm
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ld a, [wCurPartySpecies]
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cp UNOWN
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jr z, .unown
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ld a, [wCurPartySpecies]
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ld hl, PokemonPicPointers
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ld d, BANK(PokemonPicPointers)
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jr .ok
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.unown
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ld a, [wUnownLetter]
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ld hl, UnownPicPointers
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ld d, BANK(UnownPicPointers)
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.ok
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dec a
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ld bc, 6
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call AddNTimes
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```
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And `GetMonBackpic`:
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```asm
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ld a, b
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ld hl, PokemonPicPointers
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ld d, BANK(PokemonPicPointers)
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cp UNOWN
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jr nz, .ok
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ld a, c
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ld hl, UnownPicPointers
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ld d, BANK(UnownPicPointers)
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.ok
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dec a
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ld bc, 6
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call AddNTimes
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```
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## Footprints are split into top and bottom halves
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In [gfx/footprints.asm](/gfx/footprints.asm):
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```asm
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; Footprints are 2x2 tiles each, but are stored as a 16x64-tile image
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; (32 rows of 8 footprints per row).
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; That means there's a row of the top two tiles for eight footprints,
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; then a row of the bottom two tiles for those eight footprints.
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; These macros help extract the first and the last two tiles, respectively.
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footprint_top EQUS "0, 2 * LEN_1BPP_TILE"
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footprint_bottom EQUS "2 * LEN_1BPP_TILE, 2 * LEN_1BPP_TILE"
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; Entries correspond to Pokémon species, two apiece, 8 tops then 8 bottoms
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; 001-008 top halves
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INCBIN "gfx/footprints/bulbasaur.1bpp", footprint_top
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INCBIN "gfx/footprints/ivysaur.1bpp", footprint_top
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INCBIN "gfx/footprints/venusaur.1bpp", footprint_top
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INCBIN "gfx/footprints/charmander.1bpp", footprint_top
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INCBIN "gfx/footprints/charmeleon.1bpp", footprint_top
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INCBIN "gfx/footprints/charizard.1bpp", footprint_top
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INCBIN "gfx/footprints/squirtle.1bpp", footprint_top
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INCBIN "gfx/footprints/wartortle.1bpp", footprint_top
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; 001-008 bottom halves
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INCBIN "gfx/footprints/bulbasaur.1bpp", footprint_bottom
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INCBIN "gfx/footprints/ivysaur.1bpp", footprint_bottom
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INCBIN "gfx/footprints/venusaur.1bpp", footprint_bottom
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INCBIN "gfx/footprints/charmander.1bpp", footprint_bottom
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INCBIN "gfx/footprints/charmeleon.1bpp", footprint_bottom
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INCBIN "gfx/footprints/charizard.1bpp", footprint_bottom
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INCBIN "gfx/footprints/squirtle.1bpp", footprint_bottom
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INCBIN "gfx/footprints/wartortle.1bpp", footprint_bottom
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...
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```
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`Pokedex_LoadAnyFootprint` in [engine/pokedex/pokedex.asm](/engine/pokedex/pokedex.asm):
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```asm
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push hl
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ld e, l
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ld d, h
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ld hl, vTiles2 tile $62
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lb bc, BANK(Footprints), 2
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call Request1bpp
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pop hl
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; Whoever was editing footprints forgot to fix their
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; tile editor. Now each bottom half is 8 tiles off.
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ld de, 8 tiles
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add hl, de
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ld e, l
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ld d, h
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ld hl, vTiles2 tile $64
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lb bc, BANK(Footprints), 2
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call Request1bpp
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```
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**Fix:**
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Store footprints contiguously:
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```asm
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INCBIN "gfx/footprints/bulbasaur.1bpp"
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INCBIN "gfx/footprints/ivysaur.1bpp"
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INCBIN "gfx/footprints/venusaur.1bpp"
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INCBIN "gfx/footprints/charmander.1bpp"
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INCBIN "gfx/footprints/charmeleon.1bpp"
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INCBIN "gfx/footprints/charizard.1bpp"
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INCBIN "gfx/footprints/squirtle.1bpp"
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INCBIN "gfx/footprints/wartortle.1bpp"
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...
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```
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Modify `Pokedex_LoadAnyFootprint`:
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```asm
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ld e, l
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ld d, h
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ld hl, vTiles2 tile $62
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lb bc, BANK(Footprints), 4
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call Request1bpp
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```
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## `ITEM_C3` and `ITEM_DC` break up the continuous sequence of TM items
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[constants/item_constants.asm](/constants/item_constants.asm) defined the 50 TMs in order with `add_tm`, but `ITEM_C3` and `ITEM_DC` break up that sequence.
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```asm
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add_tm DYNAMICPUNCH ; bf
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...
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add_tm ROLLOUT ; c2
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const ITEM_C3 ; c3
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add_tm ROAR ; c4
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...
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add_tm DIG ; db
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const ITEM_DC ; dc
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add_tm PSYCHIC_M ; dd
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...
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add_tm NIGHTMARE ; f2
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NUM_TMS = const_value - TM01 - 2 ; discount ITEM_C3 and ITEM_DC
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```
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`GetTMHMNumber` and `GetNumberedTMHM` in [engine/items/items.asm](/engine/items/items.asm) have to compensate for this:
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```asm
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GetTMHMNumber::
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; Return the number of a TM/HM by item id c.
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ld a, c
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; Skip any dummy items.
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cp ITEM_C3 ; TM04-05
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jr c, .done
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cp ITEM_DC ; TM28-29
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jr c, .skip
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dec a
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.skip
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dec a
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.done
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sub TM01
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inc a
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ld c, a
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ret
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GetNumberedTMHM:
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; Return the item id of a TM/HM by number c.
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ld a, c
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; Skip any gaps.
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cp ITEM_C3 - (TM01 - 1)
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jr c, .done
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cp ITEM_DC - (TM01 - 1) - 1
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jr c, .skip_one
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.skip_two
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inc a
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.skip_one
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inc a
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.done
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add TM01
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dec a
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ld c, a
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ret
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```
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**Fix:**
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Move `ITEM_C3` and `ITEM_DC` above all the TMs in every table of item data.
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Modify engine/items/items.asm:
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```asm
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GetTMHMNumber::
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; Return the number of a TM/HM by item id c.
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ld a, c
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sub TM01
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inc a
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ld c, a
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ret
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GetNumberedTMHM:
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; Return the item id of a TM/HM by number c.
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ld a, c
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add TM01
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dec a
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ld c, a
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ret
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```
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## Pokédex entry banks are derived from their species IDs
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`PokedexDataPointerTable` in [data/pokemon/dex_entry_pointers.asm](/data/pokemon/dex_entry_pointers.asm) is a table of `dw`, not `dba`, yet there are four banks used for Pokédex entries. The correct bank is derived from the species ID at the beginning of each Pokémon's base stats. (This is the only use the base stat species ID has.)
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Three separate routines do the same derivation; `GetDexEntryPointer` in [engine/pokedex/pokedex_2.asm](/engine/pokedex/pokedex_2.asm):
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```asm
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GetDexEntryPointer:
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; return dex entry pointer b:de
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push hl
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ld hl, PokedexDataPointerTable
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ld a, b
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dec a
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ld d, 0
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ld e, a
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add hl, de
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add hl, de
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ld e, [hl]
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inc hl
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ld d, [hl]
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push de
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rlca
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rlca
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maskbits NUM_DEX_ENTRY_BANKS
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ld hl, .PokedexEntryBanks
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ld d, 0
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ld e, a
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add hl, de
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ld b, [hl]
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pop de
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pop hl
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ret
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.PokedexEntryBanks:
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db BANK("Pokedex Entries 001-064")
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db BANK("Pokedex Entries 065-128")
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db BANK("Pokedex Entries 129-192")
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db BANK("Pokedex Entries 193-251")
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```
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`GetPokedexEntryBank` in [engine/items/item_effects.asm](/engine/items/item_effects.asm):
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```asm
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GetPokedexEntryBank:
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push hl
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push de
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ld a, [wEnemyMonSpecies]
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rlca
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rlca
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maskbits NUM_DEX_ENTRY_BANKS
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ld hl, .PokedexEntryBanks
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ld d, 0
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ld e, a
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add hl, de
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ld a, [hl]
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pop de
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pop hl
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ret
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.PokedexEntryBanks:
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db BANK("Pokedex Entries 001-064")
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db BANK("Pokedex Entries 065-128")
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db BANK("Pokedex Entries 129-192")
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db BANK("Pokedex Entries 193-251")
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```
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And `PokedexShow_GetDexEntryBank` in [engine/pokegear/radio.asm](/engine/pokegear/radio.asm):
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```asm
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PokedexShow_GetDexEntryBank:
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push hl
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push de
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ld a, [wCurPartySpecies]
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dec a
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rlca
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rlca
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maskbits NUM_DEX_ENTRY_BANKS
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ld hl, .PokedexEntryBanks
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ld d, 0
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ld e, a
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add hl, de
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ld a, [hl]
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pop de
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pop hl
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ret
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.PokedexEntryBanks:
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db BANK("Pokedex Entries 001-064")
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db BANK("Pokedex Entries 065-128")
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db BANK("Pokedex Entries 129-192")
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db BANK("Pokedex Entries 193-251")
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```
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**Fix:** Use `dba` instead of `dw` in `PokedexDataPointerTable`, and modify the code that accesses it to match.
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## Identical sine wave code and data is repeated five times
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`_Sine` in [engine/math/sine.asm](/engine/math/sine.asm):
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```asm
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_Sine::
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; a = d * sin(e * pi/32)
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ld a, e
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calc_sine_wave
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```
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`Sprites_Cosine` and `Sprites_Sine` in [engine/gfx/sprites.asm](/engine/gfx/sprites.asm):
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```asm
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Sprites_Cosine:
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; a = d * cos(a * pi/32)
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add %010000 ; cos(x) = sin(x + pi/2)
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; fallthrough
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Sprites_Sine:
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; a = d * sin(a * pi/32)
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calc_sine_wave
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```
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`BattleAnim_Cosine` and `BattleAnim_Sine` in [engine/battle_anims/functions.asm](/engine/battle_anims/functions.asm):
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```asm
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BattleAnim_Cosine:
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; a = d * cos(a * pi/32)
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add %010000 ; cos(x) = sin(x + pi/2)
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; fallthrough
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BattleAnim_Sine:
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; a = d * sin(a * pi/32)
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calc_sine_wave BattleAnimSineWave
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...
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BattleAnimSineWave:
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sine_table 32
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```
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`StartTrainerBattle_DrawSineWave` in [engine/battle/battle_transition.asm](/engine/battle/battle_transition.asm):
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```asm
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StartTrainerBattle_DrawSineWave:
|
|
calc_sine_wave
|
|
```
|
|
|
|
And `CelebiEvent_Cosine` in [engine/events/celebi.asm](/engine/events/celebi.asm):
|
|
|
|
```asm
|
|
CelebiEvent_Cosine:
|
|
; a = d * cos(a * pi/32)
|
|
add %010000 ; cos(x) = sin(x + pi/2)
|
|
calc_sine_wave
|
|
```
|
|
|
|
They all rely on `calc_sine_wave` in [macros/code.asm](/macros/code.asm):
|
|
|
|
```asm
|
|
calc_sine_wave: MACRO
|
|
; input: a = a signed 6-bit value
|
|
; output: a = d * sin(a * pi/32)
|
|
and %111111
|
|
cp %100000
|
|
jr nc, .negative\@
|
|
call .apply\@
|
|
ld a, h
|
|
ret
|
|
.negative\@
|
|
and %011111
|
|
call .apply\@
|
|
ld a, h
|
|
xor $ff
|
|
inc a
|
|
ret
|
|
.apply\@
|
|
ld e, a
|
|
ld a, d
|
|
ld d, 0
|
|
if _NARG == 1
|
|
ld hl, \1
|
|
else
|
|
ld hl, .sinetable\@
|
|
endc
|
|
add hl, de
|
|
add hl, de
|
|
ld e, [hl]
|
|
inc hl
|
|
ld d, [hl]
|
|
ld hl, 0
|
|
.multiply\@ ; factor amplitude
|
|
srl a
|
|
jr nc, .even\@
|
|
add hl, de
|
|
.even\@
|
|
sla e
|
|
rl d
|
|
and a
|
|
jr nz, .multiply\@
|
|
ret
|
|
if _NARG == 0
|
|
.sinetable\@
|
|
sine_table 32
|
|
endc
|
|
ENDM
|
|
```
|
|
|
|
And on `sine_table` in [macros/data.asm](/macros/data.asm):
|
|
|
|
```asm
|
|
sine_table: MACRO
|
|
; \1 samples of sin(x) from x=0 to x<32768 (pi radians)
|
|
x = 0
|
|
rept \1
|
|
dw (sin(x) + (sin(x) & $ff)) >> 8 ; round up
|
|
x = x + DIV(32768, \1) ; a circle has 65536 "degrees"
|
|
endr
|
|
ENDM
|
|
```
|
|
|
|
**Fix:** Edit [home/sine.asm](/home/sine.asm) to contain a single copy of the (co)sine code in bank 0, and call it from those five sites.
|
|
|
|
|
|
## `GetForestTreeFrame` works, but it's still bad
|
|
|
|
In [engine/tilesets/tileset_anims.asm](/engine/tilesets/tileset_anims.asm):
|
|
|
|
```asm
|
|
GetForestTreeFrame:
|
|
; Return 0 if a is even, or 2 if odd.
|
|
and a
|
|
jr z, .even
|
|
cp 1
|
|
jr z, .odd
|
|
cp 2
|
|
jr z, .even
|
|
cp 3
|
|
jr z, .odd
|
|
cp 4
|
|
jr z, .even
|
|
cp 5
|
|
jr z, .odd
|
|
cp 6
|
|
jr z, .even
|
|
.odd
|
|
ld a, 2
|
|
scf
|
|
ret
|
|
.even
|
|
xor a
|
|
ret
|
|
```
|
|
|
|
**Fix:**
|
|
|
|
```asm
|
|
GetForestTreeFrame:
|
|
; Return 0 if a is even, or 2 if odd.
|
|
and 1
|
|
add a
|
|
ret
|
|
```
|