Improve the outdoor sprite system

In the tutorial to add a new map, we covered the concept of outdoor sprite sets. Outdoor maps—those with a TOWN or ROUTE environment—can only use sprites from their map group's set of usable sprites.

The outdoor sprite sets are defined in data/maps/outdoor_sprites.asm. For example, here's the one for Olivine City's map group:

OlivineGroupSprites:
	db SPRITE_SUICUNE
	db SPRITE_SILVER_TROPHY
	db SPRITE_FAMICOM
	db SPRITE_POKEDEX
	db SPRITE_WILL
	db SPRITE_KAREN
	db SPRITE_NURSE
	db SPRITE_OLD_LINK_RECEPTIONIST
	db SPRITE_STANDING_YOUNGSTER
	db SPRITE_BIG_ONIX
	db SPRITE_SUDOWOODO
	db SPRITE_BIG_SNORLAX
	db SPRITE_OLIVINE_RIVAL
	db SPRITE_POKEFAN_M
	db SPRITE_LASS
	db SPRITE_BUENA
	db SPRITE_SWIMMER_GIRL
	db SPRITE_SAILOR
	db SPRITE_POKEFAN_F
	db SPRITE_SUPER_NERD
	db SPRITE_TAUROS
	db SPRITE_FRUIT_TREE
	db SPRITE_ROCK

We can see how those get loaded with BGB's VRAM viewer:

Screenshot

VRAM is divided into six areas, each 128 tiles large. The top two areas are for sprites' standing frames. The middle-right area is for the walking frames of the sprites in the top-right. But the middle-left area is for font tiles, so the top-left sprites can't walk. (If they do, they'll appear as text tiles.)

As they're currently implemented, these sprite sets are hard to edit. Every set has 23 sprites, and it's hard to tell which ones are needed for which map. It's also not clear which sprites get placed in VRAM bank 1 (the one on the right in the VRAM viewer). There's only enough room for nine sprites to have walking frames, but those nine are not in any particular order, nor does the order of the list correspond to the order in VRAM.

This tutorial will improve the outdoor sprite sets by making them variable-length lists ending with 0, and with the first nine sprites being the ones to get walking frames. The existing sprite sets for pokecrystal's maps will be optimized to work with this new format.

1. Make outdoor sprite sets variable-length, ending with 0

Edit constants/map_data_constants.asm:

-MAX_OUTDOOR_SPRITES EQU 23 ; see engine/overworld/overworld.asm

We won't need MAX_OUTDOOR_SPRITES any more.

Next, edit engine/overworld/overworld.asm:

 AddOutdoorSprites:
 	ld a, [wMapGroup]
 	dec a
 	ld c, a
 	ld b, 0
 	ld hl, OutdoorSprites
 	add hl, bc
 	add hl, bc
 	ld a, [hli]
 	ld h, [hl]
 	ld l, a
-	ld c, MAX_OUTDOOR_SPRITES
 .loop
-	push bc
 	ld a, [hli]
+	and a
+	ret z
 	call AddSpriteGFX
-	pop bc
-	dec c
-	jr nz, .loop
-	ret
+	jr .loop

Instead of counting c down from MAX_OUTDOOR_SPRITES to 0, now AddOutdoorSprites will continue until it finds a 0 list entry. (So don't forget to add them! We'll do so later.)

Now that outdoor sprite lists can be arbitrarily long, it's more important to enforce the limit of how much RAM is even available. However, there happens to be a bug with the LoadSpriteGFX routine that ignores the SPRITE_GFX_LIST_CAPACITY limit. So be sure to fix that.

2. Don't automatically sort outdoor sprite sets

As we saw in earlier, the current sprite lists are not in any particular order. It turns out that the LoadAndSortSprites routine sorts the lists before loading their graphics, in order of how many tiles each one has, from most to least. Most NPC sprites have 12 tiles (four each for the front, back, and side views), so they get sorted first, and then come the still sprites like SPRITE_POKE_BALL, SPRITE_FRUIT_TREE, etc.

(Each outdoor sprite list gets padded to 23 entries with a bunch of still sprites like SPRITE_SILVER_TROPHY or SPRITE_OLD_LINK_RECEPTIONIST. They're not used in any outdoor map, but they have to be there so the walking sprites get sorted first.)

Anyway, edit engine/overworld/overworld.asm again:

 LoadAndSortSprites:
 	call LoadSpriteGFX
-	call SortUsedSprites
 	call ArrangeUsedSprites
 	ret

 ...

-SortUsedSprites:
-; Bubble-sort sprites by type.
-
-	...
-
-.quit
-	ret

Now sprites will be loaded into VRAM in whatever order the list specifies. So if we want a certain nine sprites to have walking frames available, we'll have to put them first.

3. Update the outdoor sprite sets

If you're replacing all of Crystal's maps with your own, you won't need these exact sets; but they're a good reference anyway for how the new sets work.

Edit [data/maps/outdoor_sprites.asm](../blob/master/data/maps/outdoor_sprites.asm): (click to expand)

-PalletGroupSprites:
-	...
-
-...
-
-CableClubGroupSprites:
-	...
+; Route1 and ViridianCity are connected
+; Route2 and PewterCity are connected
+; PalletTown and Route21 are connected
+PalletGroupSprites:
+; Route1, PalletTown
+ViridianGroupSprites:
+; Route2, Route22, ViridianCity
+PewterGroupSprites:
+; Route3, PewterCity
+CinnabarGroupSprites:
+; Route19, Route20, Route21, CinnabarIsland
+	db SPRITE_TEACHER
+	db SPRITE_FISHER
+	db SPRITE_YOUNGSTER
+	db SPRITE_BLUE
+	db SPRITE_GRAMPS
+	db SPRITE_BUG_CATCHER
+	db SPRITE_COOLTRAINER_F
+	db SPRITE_SWIMMER_GIRL
+	db SPRITE_SWIMMER_GUY
+	; limit of 9 walking sprites
+	db SPRITE_POKE_BALL
+	db SPRITE_FRUIT_TREE
+	db 0 ; end
+
+; CeruleanCity and Route5 are connected
+CeruleanGroupSprites:
+; Route4, Route9, Route10North, Route24, Route25, CeruleanCity
+SaffronGroupSprites:
+; Route5, SaffronCity
+	db SPRITE_COOLTRAINER_M
+	db SPRITE_SUPER_NERD
+	db SPRITE_COOLTRAINER_F
+	db SPRITE_FISHER
+	db SPRITE_YOUNGSTER
+	db SPRITE_LASS
+	db SPRITE_POKEFAN_M
+	db SPRITE_ROCKET
+	db SPRITE_MISTY
+	; limit of 9 walking sprites
+	db SPRITE_POKE_BALL
+	db SPRITE_SLOWPOKE
+	db 0 ; end
+
+VermilionGroupSprites:
+; Route6, Route11, VermilionCity
+	db SPRITE_POKEFAN_M
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_TEACHER
+	db SPRITE_SUPER_NERD
+	; 5 of max 9 walking sprites
+	db SPRITE_BIG_SNORLAX
+	db SPRITE_MACHOP
+	db SPRITE_POKE_BALL
+	db SPRITE_FRUIT_TREE
+	db 0 ; end
+
+CeladonGroupSprites:
+; Route7, Route16, Route17, CeladonCity
+	db SPRITE_FISHER
+	db SPRITE_TEACHER
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_LASS
+	db SPRITE_BIKER
+	; 6 of max 9 walking sprites
+	db SPRITE_POLIWAG
+	db SPRITE_POKE_BALL
+	db SPRITE_FRUIT_TREE
+	db 0 ; end
+
+; Route12 and Route13 are connected
+LavenderGroupSprites:
+; Route8, Route12, Route10South, LavenderTown
+FuchsiaGroupSprites:
+; Route13, Route14, Route15, Route18, FuchsiaCity
+	db SPRITE_POKEFAN_M
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_FISHER
+	db SPRITE_TEACHER
+	db SPRITE_SUPER_NERD
+	db SPRITE_BIKER
+	; 7 of max 9 walking sprites
+	db SPRITE_POKE_BALL
+	db SPRITE_FRUIT_TREE
+	db 0 ; end
+
+IndigoGroupSprites:
+; Route23
+	; 0 of max 9 walking sprites
+	db 0 ; end
+
+; Route29 and CherrygroveCity are connected
+NewBarkGroupSprites:
+; Route26, Route27, Route29, NewBarkTown
+CherrygroveGroupSprites:
+; Route30, Route31, CherrygroveCity
+	db SPRITE_SILVER
+	db SPRITE_TEACHER
+	db SPRITE_FISHER
+	db SPRITE_COOLTRAINER_M
+	db SPRITE_YOUNGSTER
+	db SPRITE_MONSTER
+	db SPRITE_GRAMPS
+	db SPRITE_BUG_CATCHER
+	db SPRITE_COOLTRAINER_F
+	; limit of 9 walking sprites
+	db SPRITE_POKE_BALL
+	db SPRITE_FRUIT_TREE
+	db 0 ; end
+
+; Route37 and EcruteakCity are connected
+VioletGroupSprites:
+; Route32, Route35, Route36, Route37, VioletCity
+EcruteakGroupSprites:
+; EcruteakCity
+	db SPRITE_FISHER
+	db SPRITE_LASS
+	db SPRITE_OFFICER
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_COOLTRAINER_M
+	db SPRITE_BUG_CATCHER
+	db SPRITE_SUPER_NERD
+	; 8 of max 9 walking sprites
+	db SPRITE_WEIRD_TREE ; variable sprite: becomes SPRITE_SUDOWOODO and SPRITE_TWIN
+	db SPRITE_POKE_BALL
+	db SPRITE_FRUIT_TREE
+	db SPRITE_SUICUNE
+	db 0 ; end
+
+AzaleaGroupSprites:
+; Route33, AzaleaTown
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_POKEFAN_M
+	db SPRITE_TEACHER
+	db SPRITE_AZALEA_ROCKET ; variable sprite: becomes SPRITE_ROCKET and SPRITE_SILVER
+	db SPRITE_LASS
+	; 6 of max 9 walking sprites
+	db SPRITE_FRUIT_TREE
+	db SPRITE_SLOWPOKE
+	db SPRITE_KURT_OUTSIDE ; non-walking version of SPRITE_KURT
+	db 0 ; end
+
+GoldenrodGroupSprites:
+; Route34, GoldenrodCity
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_OFFICER
+	db SPRITE_POKEFAN_M
+	db SPRITE_COOLTRAINER_F
+	db SPRITE_ROCKET
+	db SPRITE_LASS
+	; 7 of max 9 walking sprites
+	db SPRITE_DAY_CARE_MON_1
+	db SPRITE_DAY_CARE_MON_2
+	db SPRITE_POKE_BALL
+	db 0 ; end
+
+; OlivineCity and Route40 are connected
+OlivineGroupSprites:
+; Route38, Route39, OlivineCity
+CianwoodGroupSprites:
+; Route40, Route41, CianwoodCity, BattleTowerOutside
+	db SPRITE_OLIVINE_RIVAL; variable sprite: becomes SPRITE_SILVER and SPRITE_SWIMMER_GUY
+	db SPRITE_POKEFAN_M
+	db SPRITE_LASS
+	db SPRITE_BUENA
+	db SPRITE_SWIMMER_GIRL
+	db SPRITE_SAILOR
+	db SPRITE_POKEFAN_F
+	db SPRITE_SUPER_NERD
+	; 8 of max 9 walking sprites
+	db SPRITE_TAUROS
+	db SPRITE_FRUIT_TREE
+	db SPRITE_ROCK
+	db SPRITE_STANDING_YOUNGSTER ; non-walking version of SPRITE_YOUNGSTER
+	db SPRITE_SUICUNE
+	db 0 ; end
+
+MahoganyGroupSprites:
+; Route42, Route44, MahoganyTown
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_LASS
+	db SPRITE_SUPER_NERD
+	db SPRITE_COOLTRAINER_M
+	db SPRITE_POKEFAN_M
+	db SPRITE_COOLTRAINER_F
+	db SPRITE_FISHER
+	; 8 of max 9 walking sprites
+	db SPRITE_FRUIT_TREE
+	db SPRITE_POKE_BALL
+	db SPRITE_SUICUNE
+	db 0 ; end
+
+LakeOfRageGroupSprites:
+; Route43, LakeOfRage
+	db SPRITE_LANCE
+	db SPRITE_GRAMPS
+	db SPRITE_SUPER_NERD
+	db SPRITE_COOLTRAINER_F
+	db SPRITE_FISHER
+	db SPRITE_COOLTRAINER_M
+	db SPRITE_LASS
+	db SPRITE_YOUNGSTER
+	; 8 of max 9 walking sprites
+	db SPRITE_GYARADOS
+	db SPRITE_FRUIT_TREE
+	db SPRITE_POKE_BALL
+	db 0 ; end
+
+BlackthornGroupSprites:
+; Route45, Route46, BlackthornCity
+	db SPRITE_GRAMPS
+	db SPRITE_YOUNGSTER
+	db SPRITE_LASS
+	db SPRITE_SUPER_NERD
+	db SPRITE_COOLTRAINER_M
+	db SPRITE_POKEFAN_M
+	db SPRITE_BLACK_BELT
+	db SPRITE_COOLTRAINER_F
+	; 8 of max 9 walking sprites
+	db SPRITE_FRUIT_TREE
+	db SPRITE_POKE_BALL
+	db 0 ; end
+
+SilverGroupSprites:
+; Route28, SilverCaveOutside
+	; 0 of max 9 walking sprites
+	db 0 ; end
+
+DungeonsGroupSprites:
+; NationalPark, NationalParkBugContest, RuinsOfAlphOutside
+	db SPRITE_LASS
+	db SPRITE_POKEFAN_F
+	db SPRITE_TEACHER
+	db SPRITE_YOUNGSTER
+	db SPRITE_POKEFAN_M
+	db SPRITE_ROCKER
+	db SPRITE_FISHER
+	db SPRITE_SCIENTIST
+	; 8 of max 9 walking sprites
+	db SPRITE_GAMEBOY_KID
+	db SPRITE_GROWLITHE
+	db SPRITE_POKE_BALL
+	db 0 ; end
+
+FastShipGroupSprites:
+; OlivinePort, VermilionPort, MountMoonSquare, TinTowerRoof
+	db SPRITE_SAILOR
+	db SPRITE_FISHING_GURU
+	db SPRITE_SUPER_NERD
+	db SPRITE_COOLTRAINER_F
+	db SPRITE_YOUNGSTER
+	; 5 of max 9 walking sprites
+	db SPRITE_HO_OH
+	db SPRITE_FAIRY
+	db SPRITE_ROCK
+	db 0 ; end
+
+CableClubGroupSprites:
+; (no outdoor maps)
+	; 0 of max 9 walking sprites
+	db 0 ; end

Now we're done! These new sets are easier to define and debug than before. For example, here's the one for Olivine City's map group:

; OlivineCity and Route40 are connected
OlivineGroupSprites:
; Route38, Route39, OlivineCity
CianwoodGroupSprites:
; Route40, Route41, CianwoodCity, BattleTowerOutside
	db SPRITE_OLIVINE_RIVAL; variable sprite: becomes SPRITE_SILVER and SPRITE_SWIMMER_GUY
	db SPRITE_POKEFAN_M
	db SPRITE_LASS
	db SPRITE_BUENA
	db SPRITE_SWIMMER_GIRL
	db SPRITE_SAILOR
	db SPRITE_POKEFAN_F
	db SPRITE_SUPER_NERD
	; 8 of max 9 walking sprites
	db SPRITE_TAUROS
	db SPRITE_FRUIT_TREE
	db SPRITE_ROCK
	db SPRITE_STANDING_YOUNGSTER ; non-walking version of SPRITE_YOUNGSTER
	db SPRITE_SUICUNE
	db 0 ; end

And here's how they get loaded into VRAM:

Screenshot

The comments make it clear which maps the set applies to; and the order matches their order in VRAM, from top to bottom, right and then left.

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Improve the outdoor sprite system

TOC

1. Make outdoor sprite sets variable-length, ending with 0

2. Don't automatically sort outdoor sprite sets

3. Update the outdoor sprite sets

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