Fix WATERTILE/WALLTILE constants

WATRTILE was wrongly defined as 15, and WALLTILE as 1. Those had to be
flipped around.
This has allowed for us to replace inmediate values with these constants
in several places to improve readability.

WATRTILE was renamed to WATERTILE in the name of readability.

constants/tilemap_constants.asm

@@ -1,6 +1,6 @@
-LANDTILE EQU  0
-WALLTILE EQU  1
-WATRTILE EQU 15
+LANDTILE  EQU  0
+WALLTILE  EQU $f
+WATERTILE EQU  1
 
 TALK     EQU  1 << 4
 

engine/npc_movement.asm

@@ -76,7 +76,7 @@ Function6f07: ; 6f07
 	ld a, [hl]
 	ld d, a
 	call GetTileCollision
-	and a
+	and a ; land
 	jr z, Function6f3e
 	scf
 	ret
@@ -89,7 +89,7 @@ Function6f2c: ; 6f2c
 	add hl, bc
 	ld a, [hl]
 	call GetTileCollision
-	cp $1
+	cp WATERTILE
 	jr z, Function6f3e
 	scf
 	ret
@@ -210,11 +210,11 @@ Function6fa1: ; 6fa1
 	call GetCoordTile
 	call GetTileCollision
 	pop de
-	and a
+	and a ; land
 	jr nz, .asm_6fd7
 	call GetCoordTile
 	call GetTileCollision
-	and a
+	and a ; land
 	jr nz, .asm_6fd7
 	xor a
 	ret

engine/player_movement.asm

@@ -770,7 +770,7 @@ DoPlayerMovement:: ; 80000
 ; Otherwise, return carry.
 
 	call GetTileCollision
-	cp 1
+	cp WATERTILE
 	jr z, .Water
 
 ; Can walk back onto land from water.

event/overworld.asm

@@ -412,7 +412,7 @@ SurfFunction: ; c909
 	jr z, .alreadyfail
 	call GetFacingTileCoord
 	call GetTileCollision
-	cp $1
+	cp WATERTILE
 	jr nz, .cannotsurf
 	call CheckDirection
 	jr c, .cannotsurf
@@ -549,7 +549,7 @@ TrySurfOW:: ; c9e7
 ; Must be facing water.
 	ld a, [EngineBuffer1]
 	call GetTileCollision
-	cp 1 ; surfable
+	cp WATERTILE
 	jr nz, .quit
 
 ; Check tile permissions.
@@ -1522,7 +1522,7 @@ FishFunction: ; cf8e
 	jr z, .fail
 	call GetFacingTileCoord
 	call GetTileCollision
-	cp $1
+	cp WATERTILE
 	jr z, .facingwater
 .fail
 	ld a, $3
@@ -1769,7 +1769,7 @@ BikeFunction: ; d0b3
 
 .ok
 	call GetPlayerStandingTile
-	and $f ; can't use our bike in a wall or on water
+	and WALLTILE | WATERTILE ; can't use our bike in a wall or on water
 	jr nz, .nope
 	xor a
 	ret

home/map_objects.asm

@@ -84,7 +84,7 @@ GetPlayerStandingTile:: ; 184a
 CheckOnWater:: ; 1852
 	ld a, [PlayerStandingTile]
 	call GetTileCollision
-	sub 1
+	sub WATERTILE
 	ret z
 	and a
 	ret