Pull a lot of engine out of main.asm

engine/menu/start_menu.asm

@@ -0,0 +1,88 @@
+DisplayStartMenu:: ; 2acd (0:2acd)
+	ld a,$04 ; hardcoded Bank, not sure what's it refers to
+	ld [H_LOADEDROMBANK],a
+	ld [$2000],a ; ROM bank 4
+	ld a,[$d700] ; walking/biking/surfing
+	ld [$d11a],a
+	ld a, (SFX_02_3f - SFX_Headers_02) / 3 ; Start menu sound
+	call PlaySound
+
+RedisplayStartMenu:: ; 2adf (0:2adf)
+	callba DrawStartMenu
+	callba PrintSafariZoneSteps ; print Safari Zone info, if in Safari Zone
+	call UpdateSprites ; move sprites
+.loop
+	call HandleMenuInput
+	ld b,a
+.checkIfUpPressed
+	bit 6,a ; was Up pressed?
+	jr z,.checkIfDownPressed
+	ld a,[wCurrentMenuItem] ; menu selection
+	and a
+	jr nz,.loop
+	ld a,[wLastMenuItem]
+	and a
+	jr nz,.loop
+; if the player pressed tried to go past the top item, wrap around to the bottom
+	ld a,[$d74b]
+	bit 5,a ; does the player have the pokedex?
+	ld a,6 ; there are 7 menu items with the pokedex, so the max index is 6
+	jr nz,.wrapMenuItemId
+	dec a ; there are only 6 menu items without the pokedex
+.wrapMenuItemId
+	ld [wCurrentMenuItem],a
+	call EraseMenuCursor
+	jr .loop
+.checkIfDownPressed
+	bit 7,a
+	jr z,.buttonPressed
+; if the player pressed tried to go past the bottom item, wrap around to the top
+	ld a,[$d74b]
+	bit 5,a ; does the player have the pokedex?
+	ld a,[wCurrentMenuItem]
+	ld c,7 ; there are 7 menu items with the pokedex
+	jr nz,.checkIfPastBottom
+	dec c ; there are only 6 menu items without the pokedex
+.checkIfPastBottom
+	cp c
+	jr nz,.loop
+; the player went past the bottom, so wrap to the top
+	xor a
+	ld [wCurrentMenuItem],a
+	call EraseMenuCursor
+	jr .loop
+.buttonPressed ; A, B, or Start button pressed
+	call PlaceUnfilledArrowMenuCursor
+	ld a,[wCurrentMenuItem]
+	ld [$cc2d],a ; save current menu item ID
+	ld a,b
+	and a,%00001010 ; was the Start button or B button pressed?
+	jp nz,CloseStartMenu
+	call SaveScreenTilesToBuffer2 ; copy background from wTileMap to wTileMapBackup2
+	ld a,[$d74b]
+	bit 5,a ; does the player have the pokedex?
+	ld a,[wCurrentMenuItem]
+	jr nz,.displayMenuItem
+	inc a ; adjust position to account for missing pokedex menu item
+.displayMenuItem
+	cp a,0
+	jp z,StartMenu_Pokedex
+	cp a,1
+	jp z,StartMenu_Pokemon
+	cp a,2
+	jp z,StartMenu_Item
+	cp a,3
+	jp z,StartMenu_TrainerInfo
+	cp a,4
+	jp z,StartMenu_SaveReset
+	cp a,5
+	jp z,StartMenu_Option
+
+; EXIT falls through to here
+CloseStartMenu:: ; 2b70 (0:2b70)
+	call GetJoypadState
+	ld a,[H_NEWLYPRESSEDBUTTONS]
+	bit 0,a ; was A button newly pressed?
+	jr nz,CloseStartMenu
+	call LoadTextBoxTilePatterns
+	jp CloseTextDisplay