Write pending column data

src/main.s

@@ -56,10 +56,12 @@ start:
 
     call Keys_Update
 
-    ; Clear pending row state
+    ; Clear pending map state
     xor a
     ld [PENDING_ROW_PTR], a
     ld [PENDING_ROW_PTR + 1], a
+    ld [PENDING_COL_PTR], a
+    ld [PENDING_COL_PTR + 1], a
 
     call scroll_update
 
@@ -186,7 +188,6 @@ scroll_update:
     ld hl, rSCX
     ld a, [hl]
     and %111
-    cp %111
     jr nz, .update_left
 
     ld hl, CURRENT_CAMERA_X

src/map.s

@@ -12,6 +12,9 @@ LAST_SCY:: DB ; Value of SCY last frame
 PENDING_ROW_PTR:: DW ; Where to write pending row data (0 = no write)
 PENDING_ROW_DATA:: DS SCRN_VX_B ; Row to be written
 
+PENDING_COL_PTR:: DW ; Where to write pending column data (0 = no write)
+PENDING_COL_DATA: DS SCRN_VY_B ; Column to be written
+
 CURRENT_DATA_START::
 CURRENT_TILE_PTR:: DW ; Location of tile data
 CURRENT_TILE_SIZE:: DB ; Length of tile data (num_tiles * 8)
@@ -204,18 +207,39 @@ Map_Scroll::
     ret
 
 Map_Update::
-    ; Skip update if PENDING_ROW_PTR is 0
+    ; Skip row update if PENDING_ROW_PTR is 0
     ld a, [PENDING_ROW_PTR]
     ld c, a
     ld a, [PENDING_ROW_PTR + 1]
     ld b, a
     or c
-    ret z
+    jr z, .update_col
 
     ld hl, PENDING_ROW_DATA
     ld d, SCRN_VX_B
     MEMCPY bc, hl, d
 
+.update_col:
+    ; Skip update if PENDING_COL_PTR is 0
+    ld a, [PENDING_COL_PTR]
+    ld c, a
+    ld a, [PENDING_COL_PTR + 1]
+    ld b, a
+    or c
+    ret z
+
+    ld d, SCRN_VX_B
+    ld hl, PENDING_COL_DATA
+.update_col_loop:
+    ld a, [hl+]
+    ld [bc], a
+
+    ld a, SCRN_VX_B
+    ADD16 bc
+
+    dec d
+    jr nz, .update_col_loop
+
     ret
 
 ; Computes the offset into map RAM