Rename wd7ad to wStageCollisionStateBitsToSet (#50)

* Rename wd7ad

* update var name to wRedStageStructureBackup

* remove speculative comment

engine/pinball_game/ball_init/ball_init_red_field.asm

@@ -13,12 +13,12 @@ InitBallRedField: ; 0x3007d
 	xor a
 	ld [wEnableBallGravityAndTilt], a
 	ld [wd580], a
-	ld a, [wd7ad]
+	ld a, [wRedStageStructureBackup]
 	bit 7, a
 	jr z, .asm_300ae
 	ld a, [wStageCollisionState]
 	res 0, a
-	ld [wd7ad], a
+	ld [wRedStageStructureBackup], a
 .asm_300ae
 	ld a, [wStageCollisionState]
 	and $1

engine/pinball_game/ball_loss/ball_loss_red_field.asm

@@ -91,7 +91,7 @@ ConcludeSpecialMode_RedField: ; 0xddfd
 	ld [wFramesUntilSlotCaveOpens], a
 	callba ConcludeMapMoveMode
 .setCollisionState
-	ld a, [wd7ad]
+	ld a, [wRedStageStructureBackup]
 	ld c, a
 	ld a, [wStageCollisionState]
 	and $1

engine/pinball_game/evolution_mode.asm

@@ -633,7 +633,7 @@ StartEvolutionMode_RedField: ; 0x10ebb
 	ld [wLeftAlleyCount], a
 	call CloseSlotCave_
 	ld a, $2
-	ld [wd7ad], a
+	ld [wRedStageStructureBackup], a
 	ld de, MUSIC_CATCH_EM_BLUE ; Either MUSIC_CATCH_EM_BLUE or MUSIC_CATCH_EM_RED. They have the same id in their respective audio Banks.
 	call PlaySong
 	call SetPokemonSeenFlag
@@ -769,7 +769,7 @@ StartEvolutionMode_BlueField: ; 0x11061
 	ld [wLeftAlleyCount], a
 	callba CloseSlotCave
 	ld a, $2
-	ld [wd7ad], a
+	ld [wRedStageStructureBackup], a
 	ld de, MUSIC_CATCH_EM_BLUE ; Either MUSIC_CATCH_EM_BLUE or MUSIC_CATCH_EM_RED. They have the same id in their respective audio Banks.
 	call PlaySong
 	call SetPokemonSeenFlag

engine/pinball_game/map_move.asm

@@ -119,7 +119,7 @@ Func_311b4: ; 0x311b4
 	ld [wStageCollisionMap + $103], a
 	callba CloseSlotCave_
 	ld a, $4
-	ld [wd7ad], a
+	ld [wRedStageStructureBackup], a
 	ld de, MUSIC_HURRY_UP_BLUE ; Either MUSIC_HURRY_UP_BLUE or MUSIC_HURRY_UP_RED. They have the same id in their respective audio Banks.
 	call PlaySong
 	ld a, [wCurrentStage]

engine/pinball_game/object_collision/red_stage_resolve_collision.asm

@@ -1455,7 +1455,7 @@ HandleThirdRightAlleyTrigger_RedField: ; 0x15990
 
 UpdateFieldStructures_RedField: ; 0x159c9
 ; The Red field's top half has some dynamic strucutres, such as Ditto, the lightning bolt guard rail, and the roof over the 3 Voltorbs.
-	ld a, [wd7ad]
+	ld a, [wRedStageStructureBackup]
 	bit 7, a
 	ret nz
 	ld c, a
@@ -1464,7 +1464,8 @@ UpdateFieldStructures_RedField: ; 0x159c9
 	or c
 	ld [wStageCollisionState], a
 	ld a, $ff
-	ld [wd7ad], a
+	; setting 7th bit of [wStageCollisionStateBitsToSet] to 1 will cause this method to be skipped, or in this case 0xff, but only the 7th bit matters
+	ld [wRedStageStructureBackup], a
 	callba LoadStageCollisionAttributes
 	call LoadFieldStructureGraphics_RedField
 	ld a, $1
@@ -2097,7 +2098,7 @@ DoSlotLogic_RedField: ; 0x16352
 	cp EVOLUTION_MODE_SLOT_REWARD
 	ret nz
 	callba StartEvolutionMode
-	ld a, [wd7ad]
+	ld a, [wRedStageStructureBackup]
 	ld c, a
 	ld a, [wStageCollisionState]
 	and $1

engine/pinball_game/stage_init/init_red_field.asm

@@ -34,7 +34,7 @@ InitRedField: ; 0x30000
 	ld [wInitialNextBonusStage], a ; BONUS_STAGE_ORDER_DIGLETT
 	ld a, $4
 	ld [wStageCollisionState], a
-	ld [wd7ad], a
+	ld [wRedStageStructureBackup], a
 	ld a, $80
 	ld [wIndicatorStates], a
 	ld [wIndicatorStates + 3], a

wram.asm

@@ -1733,7 +1733,9 @@ wDisableHorizontalScrollForBallStart:: ; 0xd7ac
 ; 0 = Enable the scrolling
 	ds $1
 
-wd7ad:: ; 0xd7ad
+wRedStageStructureBackup:: ; 0xd7ad
+; The ditto state on red stage is heavily reliant on this value being initialized to 0b100,
+; A value of 0xff will cause this var to be ignored and treated as no changes.
 	ds $1
 
 wLeftFlipperState:: ; 0xd7ae