From b2b0cfa7c1e25cd96ecffaab18aaf799972000c1 Mon Sep 17 00:00:00 2001
From: Lukas Krickl <lukas@krickl.dev>
Date: Mon, 17 Mar 2025 17:55:14 +0100
Subject: [PATCH] scroll: Added basic scrolling to map

---
 src/player.s | 31 +++++++++++++++++++++++
 src/video.s  | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/wram.s   |  9 +++++++
 3 files changed, 110 insertions(+)

diff --git a/src/player.s b/src/player.s
index 8df7fed..f559bcf 100644
--- a/src/player.s
+++ b/src/player.s
@@ -28,16 +28,22 @@ player_update:
 
 @draw_cursor:
   ; draw cursor
+  ld a, [scroll_y]
+  ld b, a ; b = scroll_y
+  ld a, [scroll_x]
+  ld c, a ; c = scroll_x
 
   ; 8x8 small cursor
   ld hl, PLAYER_SPRITE1
 
   ld a, [cursor_y]
   add a, OBJ_OFF_Y
+  sub a, b
   ld [hl+], a
 
   ld a, [cursor_x]
   add a, OBJ_OFF_X
+  sub a, c
   ld [hl+], a
 
   ld a, CURSOR_TILE
@@ -59,6 +65,13 @@ handle_inputs:
     ld [cursor_move_timer], a
     ld a, CURSOR_MOVE_SPEED
     ld [cursor_move_y], a
+
+    
+    ; adjust scroll
+    ld a, [scroll_move_y]
+    add a, 1
+    ld [scroll_move_y], a
+
     ret
 @notdown:
   
@@ -71,6 +84,12 @@ handle_inputs:
     ld [cursor_move_timer], a
     ld a, CURSOR_MOVE_SPEED * NEGATE
     ld [cursor_move_y], a
+
+    ; adjust scroll
+    ld a, [scroll_move_y]
+    sub a, 1
+    ld [scroll_move_y], a
+    
     ret
 @notup:
 
@@ -83,6 +102,12 @@ handle_inputs:
     ld [cursor_move_timer], a
     ld a, CURSOR_MOVE_SPEED * NEGATE
     ld [cursor_move_x], a
+
+    ; adjust scroll
+    ld a, [scroll_move_x]
+    sub a, 1
+    ld [scroll_move_x], a
+
     ret
 @notleft:
 
@@ -95,6 +120,12 @@ handle_inputs:
     ld [cursor_move_timer], a
     ld a, CURSOR_MOVE_SPEED
     ld [cursor_move_x], a
+
+    ; adjust scroll
+    ld a, [scroll_move_x]
+    add a, 1
+    ld [scroll_move_x], a
+
 @notright:
 
   ret
diff --git a/src/video.s b/src/video.s
index 655a2b4..397ec51 100644
--- a/src/video.s
+++ b/src/video.s
@@ -9,10 +9,80 @@ vblank:
   call poll_inputs
   call ui_draw
 
+  call scroll_update
+
   ld a, 1
   ld [frame_ready], a
   ret
 
+  ; updates scroll based on scroll_move_y/x
+scroll_update:
+
+  ld a, [scroll_move_y]
+  cp a, 0x12
+  jr nz, @no_scroll_down REL
+
+    ; move-1
+    sub a, 1
+    ld [scroll_move_y], a
+
+    ld b, TILE_SIZE
+    ld a, [scroll_y]
+    add a, b
+    ld [scroll_y], a
+    jr @done REL
+@no_scroll_down:
+
+
+  cp a, 0xFF
+  jr nz, @no_scroll_up REL
+   
+    ; move+1
+    add a, 1
+    ld [scroll_move_y], a
+
+    ld b, TILE_SIZE
+    ld a, [scroll_y]
+    sub a, b
+    ld [scroll_y], a
+    jr @done REL
+@no_scroll_up:
+  
+
+  ld a, [scroll_move_x]
+  cp a, 0x14
+  jr nz, @no_scroll_right REL
+
+    sub a, 1
+    ld [scroll_move_x], a
+    
+    ld b, TILE_SIZE
+    ld a, [scroll_x]
+    add a, b
+    ld [scroll_x], a
+    jr @done REL
+@no_scroll_right:
+
+  cp a, 0xFF
+  jr nz, @no_scroll_left REL
+
+    add a, 1
+    ld [scroll_move_x], a
+
+    ld b, TILE_SIZE
+    ld a, [scroll_x]
+    sub a, b
+    ld [scroll_x], a
+@no_scroll_left:
+@done:
+  ld a, [scroll_y]
+  ld [RSCY], a
+
+  ld a, [scroll_x]
+  ld [RSCX], a
+
+  ret
+
   ; wait for next vblank
 vblank_wait:
   ld a, [RLY] 
diff --git a/src/wram.s b/src/wram.s
index 4dc5326..8009c43 100644
--- a/src/wram.s
+++ b/src/wram.s
@@ -32,6 +32,15 @@ cursor_move_timer: .adv 1
 cursor_move_y: .adv 1
 cursor_move_x: .adv 1
 
+  ; +/-1 for each time the cursor moves
+  ; allows us to move scroll when needed 
+scroll_move_y: .adv 1
+scroll_move_x: .adv 1
+
+  ; scroll location
+scroll_y: .adv 1
+scroll_x: .adv 1
+
 money: .adv 3
 debt: .adv 3
 demand_house: .adv 1
-- 
2.30.2