Stub out scrolling implementation

src/main.s

@@ -1,4 +1,5 @@
 INCLUDE "hardware.inc"
+INCLUDE "input.inc"
 
 SECTION "Header", ROM0[$100]
 
@@ -54,9 +55,45 @@ start:
     inc [hl]
 
     call Keys_Update
+
+    ; TODO: remove once scrolling is implemented
+    ; scroll map with arrow keys
+    ld a, [keys]
+    and BTN_UP
+    jr z, .down
+
+    ld hl, rSCY
+    dec [hl]
+
+.down:
+    ld a, [keys]
+    and BTN_DOWN
+    jr z, .right
+
+    ld hl, rSCY
+    inc [hl]
+
+.right:
+    ld a, [keys]
+    and BTN_RIGHT
+    jr z, .left
+
+    ld hl, rSCX
+    inc [hl]
+
+.left:
+    ld a, [keys]
+    and BTN_LEFT
+    jr z, .vbl
+
+    ld hl, rSCX
+    dec [hl]
+
+    call Map_Scroll
     ; call Player_Update
 
     ; wait for vblank
+.vbl:
     halt
 
     ; ~160 cycles

src/map.s

@@ -6,6 +6,9 @@ SECTION "Map Data", WRAM0
 PAGEX:: DB
 PAGEY:: DB
 
+LAST_SCX:: DB
+LAST_SCY:: DB
+
 CURRENT_DATA_START::
 CURRENT_TILE_PTR:: DW
 CURRENT_TILE_SIZE:: DB
@@ -30,10 +33,6 @@ DEF STACK_OFFSET_ROW EQU 3
 DEF STACK_OFFSET_MAP EQU 1
 DEF STACK_OFFSET_LEFT EQU 0
 
-; TODO: Don't hardcode
-DEF CAMERAX EQU 0
-DEF CAMERAY EQU 14
-
 ; Increments a 16-bit value located on the stack
 ; \1 Stack offset
 MACRO INC_STACK16
@@ -62,11 +61,13 @@ Map_Load::
     ; Initialize scroll state
     ld a, INIT_SCX
     ld [rSCX], a
+    ld [LAST_SCX], a
 
     ld a, INIT_SCY
     ld [rSCY], a
+    ld [LAST_SCY], a
 
-    xor a
+    ld a, 8
     ld [PAGEX], a
     ld [PAGEY], a
 
@@ -108,6 +109,25 @@ Map_Load::
 
     ret
 
+; Update map state based on SCX/SCY
+Map_Scroll::
+    ; Adjust CURRENT_CAMERA_X
+    ; Adjust CURRENT_CAMERA_Y
+
+    ; If SCY = PAGEY, write map row
+    ; map coords = CURRENT_CAMERA_X, CURRENT_CAMERA_Y - 2
+    ; HL = _SCRN0 + 32 * (page_y - 1)
+
+    ; If SCY = SCRN_Y - PAGEY, write map row
+    ; map coords = CURRENT_CAMERA_X, CURRENT_CAMERA_Y + 21
+    ; HL = _SCRN0 + 32 * ((32 - page_y) - 1)
+    ; TODO: Check math on these
+
+    ; If SCX = PAGEX, write map col
+    ; If SCX = SCRN_X - PAGEX, write map col
+
+    ret
+
 ; Write a row of map data into map RAM
 ; @param b Map X coordinate (signed)
 ; @param c Map Y coordinate (signed)