Add old map copying routine back for map initialization

src/map.s

@@ -171,8 +171,6 @@ Map_Scroll::
     jr .loop
 
 .write_up:
-    ; halt
-    ; call write_map_row
     call enqueue_row_write
 
     ld a, [PAGEY]
@@ -306,3 +304,159 @@ enqueue_row_write:
     dec c
     jr nz, .zero_row_loop
     ret
+
+; TODO: Deduplicate with enqueue_row_write? This version is needed when
+; loading a map, which happens synchronously while LCD is disabled
+;
+; Write a row of map data into map RAM
+; @param b Map X coordinate (signed)
+; @param c Map Y coordinate (signed)
+; @param hl Pointer into map VRAM
+write_map_row:
+    push bc
+    push de
+
+    ; If Y < 0, write a row of 0s
+    bit 7, c
+    jr nz, .zero_row
+
+    ; If Y >= MAP_HEIGHT, write a row of 0s
+    ld a, [CURRENT_MAP_HEIGHT]
+    dec a
+    cp c
+    jr nc, .begin_writing
+
+.zero_row:
+    ld d, SCRN_VX_B
+    xor a
+.zero_row_loop:
+    ld a, [hl+]
+    dec d
+    jr nz, .zero_row_loop
+.zero_row_done:
+    pop de
+    pop bc
+    ret
+
+.begin_writing:
+    push hl
+
+    ; Allocate 2 bytes for map pointer
+    ; Allocate 1 byte for number of tiles left
+    add sp, -3
+
+    ; left = number of tiles left to write
+    ld hl, sp + STACK_OFFSET_LEFT
+    ld [hl], SCRN_VX_B
+
+    ; HL = CURRENT_MAP_PTR + Y * CURRENT_MAP_HEIGHT
+    ld a, [CURRENT_MAP_PTR]
+    ld l, a
+    ld a, [CURRENT_MAP_PTR + 1]
+    ld h, a
+
+.compute_map_row:
+    ld a, c
+    or a
+    jr z, .compute_map_row_done
+
+    ld a, [CURRENT_MAP_HEIGHT]
+    ADD16 HL
+    dec c
+    jr .compute_map_row
+
+    ; map = HL
+.compute_map_row_done:
+    LD16 de, hl
+    ld hl, sp + STACK_OFFSET_MAP
+    ld a, e
+    ld [hl+], a
+    ld a, d
+    ld [hl], a
+
+    ld hl, sp + STACK_OFFSET_LEFT
+
+    ; While X < 0 and left > 0, write 0 to the row
+.pad_left:
+    bit 7, b
+    jr z, .copy_center
+
+    ld a, [hl]
+    or a
+    jr z, .done
+
+    ; *row = 0
+    ZERO_ROW_TILE
+
+    ; row++
+    INC_STACK16 STACK_OFFSET_ROW
+
+    ; X++, left--
+    inc b
+    ld hl, sp + STACK_OFFSET_LEFT
+    dec [hl]
+    jr .pad_left
+
+    ; While X < MAP_WIDTH and [SP] > 0, copy from map
+.copy_center:
+    ld a, [CURRENT_MAP_WIDTH]
+    dec a
+    cp b
+    jr z, .pad_right
+
+    ld a, [hl]
+    or a
+    jr z, .done
+
+    ; A = *map_ptr
+    ld hl, sp + STACK_OFFSET_MAP
+    ld a, [hl+]
+    ld e, a
+    ld d, [hl]
+    ld a, [de]
+
+    ; map_ptr++
+    INC_STACK16 STACK_OFFSET_MAP
+
+    ; *row = A
+    ld hl, sp + STACK_OFFSET_ROW
+    ld e, [hl]
+    inc hl
+    ld d, [hl]
+    ld [de], a
+
+    ; row++
+    INC_STACK16 3
+
+    ; X++, [SP]--
+.copy_center_inc:
+    inc b
+    ld hl, sp + STACK_OFFSET_LEFT
+    dec [hl]
+    jr .copy_center
+
+    ; While [SP] > 0, write 0 to the row
+.pad_right:
+    ld a, [hl]
+    or a
+    jr z, .done
+
+    ; *row = 0
+    ZERO_ROW_TILE
+
+    ; row++
+    INC_STACK16 STACK_OFFSET_ROW
+
+    ; [SP]--
+.pad_right_inc:
+    ld hl, sp + STACK_OFFSET_ROW
+    dec [hl]
+    jr .pad_right
+
+.done:
+    add sp, 3
+    pop hl
+    pop de
+    pop bc
+
+    ret