From fb6721f9cfad425fabf54371bb6225bfb53ae917 Mon Sep 17 00:00:00 2001
From: Forest Belton <65484+forestbelton@users.noreply.github.com>
Date: Sun, 11 Jul 2021 20:09:32 -0400
Subject: [PATCH] Finish implementing vertical scrolling

---
 src/map.s | 33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/src/map.s b/src/map.s
index ca6431d..5f68d40 100644
--- a/src/map.s
+++ b/src/map.s
@@ -30,8 +30,6 @@ SECTION "Map Code", ROM0
 DEF INIT_SCX EQUS "((SCRN_VX - SCRN_X) / 2)"
 DEF INIT_SCY EQUS "((SCRN_VY - SCRN_Y) / 2)"
 
-DEF PAGE_SIZE EQU 2
-
 DEF STACK_OFFSET_ROW EQU 3
 DEF STACK_OFFSET_MAP EQU 1
 DEF STACK_OFFSET_LEFT EQU 0
@@ -180,21 +178,34 @@ Map_Scroll::
     jr .done
 
 .scroll_down_check:
-    ; Check SCY + SCRN_Y = PAGEY
+    ; Check SCY + (SCRN_Y + 16) = PAGEY
     ld a, [PAGEY]
-    sub SCRN_Y
+    sub SCRN_Y + 16
     ld hl, rSCY
     cp [hl]
     jr nz, .done
 
+    ld a, [PAGEY]
+    srl a
+    srl a
+    srl a
+    dec a
+    ld e, a
+    call compute_vram_ptr
+
+    ; B = CAMERA_X - SCX/8
+    ld a, [rSCX]
+    ld b, a
     ld a, [CURRENT_CAMERA_X]
+    srl b
+    srl b
+    srl b
+    sub b
     ld b, a
 
     ld a, [CURRENT_CAMERA_Y]
-    add SCRN_X_B + 1
+    add SCRN_Y_B + 1
     ld c, a
-
-    call compute_vram_ptr
     call enqueue_row_write
 
     ld a, [PAGEY]
@@ -353,7 +364,7 @@ enqueue_row_write:
     xor a
     ld c, SCRN_VX_B
 .zero_row_loop:
-    ld a, [hl+]
+    ld [hl+], a
     dec c
     jr nz, .zero_row_loop
     ret
@@ -384,7 +395,7 @@ write_map_row:
     ld d, SCRN_VX_B
     xor a
 .zero_row_loop:
-    ld a, [hl+]
+    ld [hl+], a
     dec d
     jr nz, .zero_row_loop
 .zero_row_done:
@@ -403,7 +414,7 @@ write_map_row:
     ld hl, sp + STACK_OFFSET_LEFT
     ld [hl], SCRN_VX_B
 
-    ; HL = CURRENT_MAP_PTR + Y * CURRENT_MAP_HEIGHT
+    ; HL = CURRENT_MAP_PTR + Y * CURRENT_MAP_WIDTH
     ld a, [CURRENT_MAP_PTR]
     ld l, a
     ld a, [CURRENT_MAP_PTR + 1]
@@ -414,7 +425,7 @@ write_map_row:
     or a
     jr z, .compute_map_row_done
 
-    ld a, [CURRENT_MAP_HEIGHT]
+    ld a, [CURRENT_MAP_WIDTH]
     ADD16 HL
     dec c
     jr .compute_map_row