From 225ef5c50cb6956cf0a6218ea42a33ecff6525b5 Mon Sep 17 00:00:00 2001
From: Lukas Krickl <lukas@krickl.dev>
Date: Sat, 20 Sep 2025 13:40:45 +0200
Subject: [PATCH] map: wip map scrolling

---
 src/defs.s   |  9 +++++++++
 src/player.s | 28 ++++++++++++++++++++++++++++
 src/video.s  | 24 ++++++++++++++++++++++++
 src/wram.s   |  7 +++++++
 4 files changed, 68 insertions(+)

diff --git a/src/defs.s b/src/defs.s
index ae493a7..319a96b 100644
--- a/src/defs.s
+++ b/src/defs.s
@@ -17,6 +17,8 @@
 #define MAP_OBJ_MAX 32
 #define RECT_MAX 32
 
+#define MAP_ROW_H 16 ; pixels per row
+
 #define STACK_BEGIN 0xDFFF
 
   ; seed for the rng
@@ -124,3 +126,10 @@
 .de r_h, 1
 .de r_w, 1
 .de r_size, 0
+
+
+	; gameplay control flags
+.se 1
+.de GPF_NO_SCROLL, 1
+	; scroll a row up next vblank
+.de GPF_SCROLL, 2
diff --git a/src/player.s b/src/player.s
index 31e966c..e0eb4f5 100644
--- a/src/player.s
+++ b/src/player.s
@@ -10,6 +10,9 @@ player_init:
 
 	ld a, 0 
 	ld [player+act_pos_y_hi], a
+
+	ld a, 0xA0 ; initial next scroll
+	ld [player_next_scroll_y], a
 	ret
 	
 	; updates the special player actor
@@ -21,6 +24,7 @@ player_update:
 		ld c, 0
 		call player_stage_move_n
 		call player_try_move
+		call player_try_scroll_up
 @not_up:
 
 	ld b, BTNDOWN
@@ -56,6 +60,30 @@ player_update:
 
 #define PLAYER_SPRITE_IDLE1 0x8D
 	
+	; if the player's real y position is over
+	; a certain value we should scroll the map
+	; if scrolling is allowed
+	; inputs:
+	;		player setp up counter
+player_try_scroll_up:
+	ld a, [game_flags]
+	and a, GPF_NO_SCROLL
+	ret nz ; no scroll allowed for now
+	
+	ld a, [player_next_scroll_y]
+	ld b, a 
+	ld a, [player+act_pos_y]
+	cp a, b
+	jp nc, @no_scroll
+
+		ld a, [game_flags]
+		or a, GPF_SCROLL
+		ld [game_flags], a
+
+	
+@no_scroll:
+	ret
+	
 	; stages a move in a positive directon
 	; inputs:
 	;		b/c: y/x movement
diff --git a/src/video.s b/src/video.s
index 82a8cda..7a22390 100644
--- a/src/video.s
+++ b/src/video.s
@@ -14,6 +14,8 @@ vblank:
   ; dma previous frame's oam
   call OAMDMAFN
 
+	call video_map_perform_scroll
+
   call scroll_write
   
   ; get inputs 
@@ -23,6 +25,28 @@ vblank:
   ld [frame_ready], a
   pop_all
   ret
+	
+	; scrolls if the flag is set
+video_map_perform_scroll:
+	ld a, [game_flags]
+	and a, GPF_SCROLL
+	ret z
+
+	ld a, [scroll_y]
+	sub a, MAP_ROW_H
+	ld [scroll_y], a
+
+	ld a, [player_next_scroll_y]
+	sub a, MAP_ROW_H
+	ld [player_next_scroll_y], a
+	
+	call map_advance_row
+
+	; unset flag
+	ld a, [game_flags]
+	and a, ~GPF_SCROLL & 0xFF
+	ld [game_flags], a
+	ret
 
 
   ; writes scroll to scroll registers
diff --git a/src/wram.s b/src/wram.s
index c26d6dd..adb6125 100644
--- a/src/wram.s
+++ b/src/wram.s
@@ -39,6 +39,9 @@ vblank_jp: .adv 4
   ; of the input list
   ; if set to NULL do not read from this address
 demo_inputs: .adv 2
+	
+	; gameplay control flags
+game_flags: .adv 1
 
 ; dummy oam 
 ; same memory as empty_unit
@@ -53,6 +56,10 @@ scroll_x: .adv 1
   ; 16 bit srand seed
   ; seed must never be 0
 srand: .adv 2
+	
+	; if player y < next_scroll
+	; advance if possible
+player_next_scroll_y: .adv 1
 
 
 player: .adv act_size
-- 
2.30.2