Implement Waterfall technique (#34)

engine/events/overworld.asm

@@ -667,7 +667,7 @@ WaterfallFunction:
 	ld a, $80
 	ret
 
-CheckMapCanWaterfall:
+CheckMapCanWaterfall::
 	ld a, [wPlayerDirection]
 	and $c
 	cp FACE_UP
@@ -682,6 +682,19 @@ CheckMapCanWaterfall:
 	scf
 	ret
 
+Script_WaterfallAuto::
+.loop
+	playsound SFX_SURF
+	applymovement PLAYER, .SlowStepUp
+	callasm CheckContinueWaterfall
+	iffalse .loop
+	callasm SFXChannelsOff ; end SFX_SURF if still playing
+	end
+
+.SlowStepUp:
+	slow_step UP
+	step_end
+
 Script_WaterfallFromMenu:
 	reloadmappart
 	special UpdateTimePals
@@ -693,12 +706,16 @@ Script_UsedWaterfall:
 	closetext
 	playsound SFX_BUBBLEBEAM
 .loop
-	applymovement PLAYER, .WaterfallStep
-	callasm .CheckContinueWaterfall
+	applymovement PLAYER, WaterfallStep
+	callasm CheckContinueWaterfall
 	iffalse .loop
 	end
 
-.CheckContinueWaterfall:
+.UseWaterfallText:
+	text_far _UseWaterfallText
+	text_end
+
+CheckContinueWaterfall:
 	xor a
 	ldh [hScriptVar], a
 	ld a, [wPlayerTile]
@@ -708,14 +725,10 @@ Script_UsedWaterfall:
 	ldh [hScriptVar], a
 	ret
 
-.WaterfallStep:
+WaterfallStep:
 	turn_waterfall UP
 	step_end
 
-.UseWaterfallText:
-	text_far _UseWaterfallText
-	text_end
-
 TryWaterfallOW::
 	ld d, WATERFALL
 	call CheckPartyMove

engine/overworld/events.asm

@@ -769,6 +769,22 @@ CheckFacingTileEvent:
 	ret ; c
 
 .next_event_1
+;; Waterfall
+	ld a, [wFacingTileID]
+	call CheckWaterfallTile
+	jr nz, .next_event_2
+
+; Must be facing up and facing a waterfall tile to trigger the waterfall up sequence.
+; Otherwise HI_NYBBLE_CURRENT collision (forced walking in walking direction) applies.
+	farcall CheckMapCanWaterfall
+	jr c, .next_event_2
+
+	ld a, BANK(Script_WaterfallAuto)
+	ld hl, Script_WaterfallAuto
+	call CallScript
+	ret ; c
+
+.next_event_2
 .no_event
 	xor a
 	ret ; nc

engine/overworld/player_movement.asm

@@ -340,7 +340,7 @@ DoPlayerMovement::
 	add hl, bc
 	ld a, [hl]
 	ld [wWalkingDirection], a
-	jr .continue_walk
+	jr .continue_fast_slide
 
 .water_table
 	db RIGHT ; COLL_WATERFALL_RIGHT
@@ -414,8 +414,15 @@ DoPlayerMovement::
 	xor a
 	ret
 
+.continue_fast_slide
+	ld a, STEP_ICE
+	jr .continue_step
+
 .continue_walk
 	ld a, STEP_WALK
+	; fallthrough
+
+.continue_step
 	call .DoStep
 	ld a, PLAYERMOVEMENT_CONTINUE
 	scf