ref: 80d437d56562e3ec75f2b2fbc05443f4d2cbc0b4
dir: /docs/design_flaws.md/
# Design Flaws 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)). ## Contents - [Pic banks are offset by `PICS_FIX`](#pic-banks-are-offset-by-pics_fix) - [`PokemonPicPointers` and `UnownPicPointers` are assumed to start at the same address](#pokemonpicpointers-and-unownpicpointers-are-assumed-to-start-at-the-same-address) - [Footprints are split into top and bottom halves](#footprints-are-split-into-top-and-bottom-halves) - [`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) - [Pokédex entry banks are derived from their species IDs](#pokédex-entry-banks-are-derived-from-their-species-ids) - [Identical sine wave code and data is repeated five times](#identical-sine-wave-code-and-data-is-repeated-five-times) - [`GetForestTreeFrame` works, but it's still bad](#getforesttreeframe-works-but-its-still-bad) ## Pic banks are offset by `PICS_FIX` [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`: ```asm dba_pic: MACRO ; dbw bank, address db BANK(\1) - PICS_FIX dw \1 ENDM ``` The offset is translated into a correct bank by `FixPicBank` in [engine/gfx/load_pics.asm](/engine/gfx/load_pics.asm): ```asm FixPicBank: ; 511c5 ; This is a thing for some reason. PICS_FIX EQU $36 GLOBAL PICS_FIX push hl push bc sub BANK(Pics_1) - PICS_FIX ld c, a ld b, 0 ld hl, .PicsBanks add hl, bc ld a, [hl] pop bc pop hl ret .PicsBanks: ; 511d4 db BANK(Pics_1) + 0 db BANK(Pics_1) + 1 db BANK(Pics_1) + 2 db BANK(Pics_1) + 3 db BANK(Pics_1) + 4 db BANK(Pics_1) + 5 db BANK(Pics_1) + 6 db BANK(Pics_1) + 7 db BANK(Pics_1) + 8 db BANK(Pics_1) + 9 db BANK(Pics_1) + 10 db BANK(Pics_1) + 11 db BANK(Pics_1) + 12 db BANK(Pics_1) + 13 db BANK(Pics_1) + 14 db BANK(Pics_1) + 15 db BANK(Pics_1) + 16 db BANK(Pics_1) + 17 db BANK(Pics_1) + 18 db BANK(Pics_1) + 19 db BANK(Pics_1) + 20 db BANK(Pics_1) + 21 db BANK(Pics_1) + 22 db BANK(Pics_1) + 23 ``` **Fix:** Use `dba` instead of `dba_pic`, and don't call `FixPicBank` to modify `a`. ## `PokemonPicPointers` and `UnownPicPointers` are assumed to start at the same address In [gfx/pics.asm](/gfx/pics.asm): ```asm ; PokemonPicPointers and UnownPicPointers are assumed to start at the same ; address, but in different banks. This is enforced in pokecrystal.link. SECTION "Pic Pointers", ROMX INCLUDE "data/pokemon/pic_pointers.asm" SECTION "Unown Pic Pointers", ROMX INCLUDE "data/pokemon/unown_pic_pointers.asm" ``` In [pokecrystal.link](/pokecrystal.link): ``` ROMX $48 org $4000 "Pic Pointers" "Pics 1" ROMX $49 org $4000 "Unown Pic Pointers" "Pics 2" ``` Two routines in [engine/gfx/load_pics.asm](/engine/gfx/load_pics.asm) make this assumption; `GetFrontpicPointer`: ```asm ld a, [wCurPartySpecies] cp UNOWN jr z, .unown ld a, [wCurPartySpecies] ld d, BANK(PokemonPicPointers) jr .ok .unown ld a, [wUnownLetter] ld d, BANK(UnownPicPointers) .ok ld hl, PokemonPicPointers ; UnownPicPointers dec a ld bc, 6 call AddNTimes ``` And `GetMonBackpic`: ```asm ; These are assumed to be at the same address in their respective banks. ld hl, PokemonPicPointers ; UnownPicPointers ld a, b ld d, BANK(PokemonPicPointers) cp UNOWN jr nz, .ok ld a, c ld d, BANK(UnownPicPointers) .ok dec a ld bc, 6 call AddNTimes ``` **Fix:** Don't enforce `org $4000` in pokecrystal.link. Modify `GetFrontpicPointer`: ```asm ld a, [wCurPartySpecies] cp UNOWN jr z, .unown ld a, [wCurPartySpecies] ld hl, PokemonPicPointers ld d, BANK(PokemonPicPointers) jr .ok .unown ld a, [wUnownLetter] ld hl, UnownPicPointers ld d, BANK(UnownPicPointers) .ok dec a ld bc, 6 call AddNTimes ``` And `GetMonBackpic`: ```asm ld a, b ld hl, PokemonPicPointers ld d, BANK(PokemonPicPointers) cp UNOWN jr nz, .ok ld a, c ld hl, UnownPicPointers ld d, BANK(UnownPicPointers) .ok dec a ld bc, 6 call AddNTimes ``` ## Footprints are split into top and bottom halves In [gfx/footprints.asm](/gfx/footprints.asm): ```asm ; Footprints are 2x2 tiles each, but are stored as a 16x64-tile image ; (32 rows of 8 footprints per row). ; That means there's a row of the top two tiles for eight footprints, ; then a row of the bottom two tiles for those eight footprints. ; These macros help extract the first and the last two tiles, respectively. footprint_top EQUS "0, 2 * LEN_1BPP_TILE" footprint_bottom EQUS "2 * LEN_1BPP_TILE, 2 * LEN_1BPP_TILE" ; Entries correspond to Pokémon species, two apiece, 8 tops then 8 bottoms ; 001-008 top halves INCBIN "gfx/footprints/bulbasaur.1bpp", footprint_top INCBIN "gfx/footprints/ivysaur.1bpp", footprint_top INCBIN "gfx/footprints/venusaur.1bpp", footprint_top INCBIN "gfx/footprints/charmander.1bpp", footprint_top INCBIN "gfx/footprints/charmeleon.1bpp", footprint_top INCBIN "gfx/footprints/charizard.1bpp", footprint_top INCBIN "gfx/footprints/squirtle.1bpp", footprint_top INCBIN "gfx/footprints/wartortle.1bpp", footprint_top ; 001-008 bottom halves INCBIN "gfx/footprints/bulbasaur.1bpp", footprint_bottom INCBIN "gfx/footprints/ivysaur.1bpp", footprint_bottom INCBIN "gfx/footprints/venusaur.1bpp", footprint_bottom INCBIN "gfx/footprints/charmander.1bpp", footprint_bottom INCBIN "gfx/footprints/charmeleon.1bpp", footprint_bottom INCBIN "gfx/footprints/charizard.1bpp", footprint_bottom INCBIN "gfx/footprints/squirtle.1bpp", footprint_bottom INCBIN "gfx/footprints/wartortle.1bpp", footprint_bottom ... ``` `Pokedex_LoadAnyFootprint` in [engine/pokedex/pokedex.asm](/engine/pokedex/pokedex.asm): ```asm push hl ld e, l ld d, h ld hl, vTiles2 tile $62 lb bc, BANK(Footprints), 2 call Request1bpp pop hl ; Whoever was editing footprints forgot to fix their ; tile editor. Now each bottom half is 8 tiles off. ld de, 8 tiles add hl, de ld e, l ld d, h ld hl, vTiles2 tile $64 lb bc, BANK(Footprints), 2 call Request1bpp ``` **Fix:** Store footprints contiguously: ```asm INCBIN "gfx/footprints/bulbasaur.1bpp" INCBIN "gfx/footprints/ivysaur.1bpp" INCBIN "gfx/footprints/venusaur.1bpp" INCBIN "gfx/footprints/charmander.1bpp" INCBIN "gfx/footprints/charmeleon.1bpp" INCBIN "gfx/footprints/charizard.1bpp" INCBIN "gfx/footprints/squirtle.1bpp" INCBIN "gfx/footprints/wartortle.1bpp" ... ``` Modify `Pokedex_LoadAnyFootprint`: ```asm ld e, l ld d, h ld hl, vTiles2 tile $62 lb bc, BANK(Footprints), 4 call Request1bpp ``` ## `ITEM_C3` and `ITEM_DC` break up the continuous sequence of TM items [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. ```asm add_tm DYNAMICPUNCH ; bf ... add_tm ROLLOUT ; c2 const ITEM_C3 ; c3 add_tm ROAR ; c4 ... add_tm DIG ; db const ITEM_DC ; dc add_tm PSYCHIC_M ; dd ... add_tm NIGHTMARE ; f2 NUM_TMS = const_value - TM01 - 2 ; discount ITEM_C3 and ITEM_DC ``` `GetTMHMNumber` and `GetNumberedTMHM` in [engine/items/items.asm](/engine/items/items.asm) have to compensate for this: ```asm GetTMHMNumber:: ; d407 ; Return the number of a TM/HM by item id c. ld a, c ; Skip any dummy items. cp ITEM_C3 ; TM04-05 jr c, .done cp ITEM_DC ; TM28-29 jr c, .skip dec a .skip dec a .done sub TM01 inc a ld c, a ret GetNumberedTMHM: ; d417 ; Return the item id of a TM/HM by number c. ld a, c ; Skip any gaps. cp ITEM_C3 - (TM01 - 1) jr c, .done cp ITEM_DC - (TM01 - 1) - 1 jr c, .skip_one .skip_two inc a .skip_one inc a .done add TM01 dec a ld c, a ret ``` **Fix:** Move `ITEM_C3` and `ITEM_DC` above all the TMs in every table of item data. Modify engine/items/items.asm: ```asm GetTMHMNumber:: ; d407 ; Return the number of a TM/HM by item id c. ld a, c sub TM01 inc a ld c, a ret GetNumberedTMHM: ; d417 ; Return the item id of a TM/HM by number c. ld a, c add TM01 dec a ld c, a ret ``` ## Pokédex entry banks are derived from their species IDs `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.) Three separate routines do the same derivation; `GetDexEntryPointer` in [engine/pokedex/pokedex_2.asm](/engine/pokedex/pokedex_2.asm): ```asm GetDexEntryPointer: ; 44333 ; return dex entry pointer b:de push hl ld hl, PokedexDataPointerTable ld a, b dec a ld d, 0 ld e, a add hl, de add hl, de ld e, [hl] inc hl ld d, [hl] push de rlca rlca maskbits NUM_DEX_ENTRY_BANKS ld hl, .PokedexEntryBanks ld d, 0 ld e, a add hl, de ld b, [hl] pop de pop hl ret .PokedexEntryBanks: db BANK(PokedexEntries1) db BANK(PokedexEntries2) db BANK(PokedexEntries3) db BANK(PokedexEntries4) ``` `GetPokedexEntryBank` in [engine/items/item_effects.asm](/engine/items/item_effects.asm): ```asm GetPokedexEntryBank: push hl push de ld a, [wEnemyMonSpecies] rlca rlca maskbits NUM_DEX_ENTRY_BANKS ld hl, .PokedexEntryBanks ld d, 0 ld e, a add hl, de ld a, [hl] pop de pop hl ret .PokedexEntryBanks: db BANK(PokedexEntries1) db BANK(PokedexEntries2) db BANK(PokedexEntries3) db BANK(PokedexEntries4) ``` And `PokedexShow_GetDexEntryBank` in [engine/pokegear/radio.asm](/engine/pokegear/radio.asm): ```asm PokedexShow_GetDexEntryBank: push hl push de ld a, [wCurPartySpecies] dec a rlca rlca maskbits NUM_DEX_ENTRY_BANKS ld hl, .PokedexEntryBanks ld d, 0 ld e, a add hl, de ld a, [hl] pop de pop hl ret .PokedexEntryBanks: db BANK(PokedexEntries1) db BANK(PokedexEntries2) db BANK(PokedexEntries3) db BANK(PokedexEntries4) ``` **Fix:** Use `dba` instead of `dw` in `PokedexDataPointerTable`, and modify the code that accesses it to match. ## Identical sine wave code and data is repeated five times `_Sine` in [engine/math/sine.asm](/engine/math/sine.asm): ```asm _Sine:: ; 84d9 ; a = d * sin(e * pi/32) ld a, e calc_sine_wave ``` `Sprites_Cosine` and `Sprites_Sine` in [engine/gfx/sprites.asm](/engine/gfx/sprites.asm): ```asm Sprites_Cosine: ; 8e72a ; a = d * cos(a * pi/32) add %010000 ; cos(x) = sin(x + pi/2) ; fallthrough Sprites_Sine: ; 8e72c ; a = d * sin(a * pi/32) calc_sine_wave ``` `BattleAnim_Cosine` and `BattleAnim_Sine` in [engine/battle_anims/functions.asm](/engine/battle_anims/functions.asm): ```asm BattleAnim_Cosine: ; ce732 (33:6732) ; a = d * cos(a * pi/32) add %010000 ; cos(x) = sin(x + pi/2) ; fallthrough BattleAnim_Sine: ; ce734 (33:6734) ; a = d * sin(a * pi/32) calc_sine_wave BattleAnimSineWave ... BattleAnimSineWave: ; ce77f sine_table 32 ; ce7bf ``` `StartTrainerBattle_DrawSineWave` in [engine/battle/battle_transition.asm](/engine/battle/battle_transition.asm): ```asm StartTrainerBattle_DrawSineWave: ; 8c6f7 (23:46f7) calc_sine_wave ; 8c768 ``` And `CelebiEvent_Cosine` in [engine/events/celebi.asm](/engine/events/celebi.asm): ```asm CelebiEvent_Cosine: ; 49b3b (12:5b3b) ; a = d * cos(a * pi/32) add %010000 ; cos(x) = sin(x + pi/2) calc_sine_wave ; 49bae ``` 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: ; fc54c ; 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 ; fc56d ``` **Fix:** ```asm GetForestTreeFrame: ; fc54c ; Return 0 if a is even, or 2 if odd. and 1 add a ret ; fc56d ```