diff --git a/th04/formats/cdg_put_plane.asm b/th04/formats/cdg_put_plane.asm
new file mode 100644
index 00000000..80547f51
--- /dev/null
+++ b/th04/formats/cdg_put_plane.asm
@@ -0,0 +1,97 @@
+; Displays the given [plane] of the CDG image in the given [slot] at (x, y).
+; (Unlike other CDG displaying functions, this one actually accepts any value
+; for X.) Assumes the GRCG to be set to monochrome mode.
+;
+; (This is used for the "dissolution effect" in the staff roll, but it
+; actually doesn't apply any sort of effect on the pixel data, and relies on
+; the individual planes being pre-dissolved.)
+
+; void pascal cdg_put_plane(int x, int y, int slot, int plane)
+public _cdg_put_plane
+_cdg_put_plane	proc far
+
+@@plane	= word ptr  6
+@@slot 	= word ptr  8
+@@y    	= word ptr  0Ah
+@@x    	= word ptr  0Ch
+
+	push	bp
+	mov	bp, sp
+	push	si
+	push	di
+	mov	si, [bp+@@slot]
+	shl	si, 4
+	add	si, offset _cdg_slots
+	mov	cx, [bp+@@x]
+	mov	di, cx
+	sar	di, 4
+	shl	di, 1
+	add	di, [si+CDGSlot.vram_byte_at_bottom_left]
+	mov	ax, [si+CDGSlot.width_divided_by_32]
+	shl	ax, 1
+	mov	byte ptr cs:@@width_words+1, al
+	and	cx, 15
+	mov	bx, cx
+	shl	bx, 1
+	mov	bx, WORD_PUT_PATTERN[bx]
+	mov	word ptr cs:@@put_pattern_1+1, bx
+	mov	word ptr cs:@@put_pattern_2+1, bx
+	jmp	short $+2
+	shl	ax, 1
+	add	ax, (640 / 8)
+	mov	dx, ax
+	mov	ax, [bp+@@y]
+	mov	bx, ax
+	shl	ax, 2
+	add	ax, bx
+	add	ax, 0A800h
+	mov	es, ax
+	push	ds
+	mov	ax, [si+CDGSlot.sgm_colors]
+	mov	si, [si+CDGSlot.bitplane_size]
+	mov	ds, ax
+	mov	ax, [bp+@@plane]
+	mov	bp, dx
+	mul	si
+	mov	si, ax
+	cld
+
+@@width_words:
+	mov	ch, 80h
+	lodsw
+	ror	ax, cl
+	mov	dx, ax
+
+@@put_pattern_1:
+	and	ax, 1234h
+	xor	dx, ax
+	stosw
+	dec	ch
+
+@@blit_word:
+	lodsw
+	ror	ax, cl
+	mov	bx, ax
+
+@@put_pattern_2:
+	and	ax, 1234h
+	xor	bx, ax
+	or	ax, dx
+	mov	dx, bx
+	stosw
+	dec	ch
+	jnz	short @@blit_word
+	or	dx, dx
+	jz	short @@next_row
+	mov	es:[di], dx
+	xor	dx, dx
+
+@@next_row:
+	sub	di, bp
+	jns	short @@width_words
+	pop	ds
+	pop	di
+	pop	si
+	pop	bp
+	retf	8
+_cdg_put_plane	endp
diff --git a/th04/formats/cdg_put_plane[data].asm b/th04/formats/cdg_put_plane[data].asm
new file mode 100644
index 00000000..2d9a85e7
--- /dev/null
+++ b/th04/formats/cdg_put_plane[data].asm
@@ -0,0 +1,19 @@
+; Masks the bits of an 1bpp image word that should be written to the first
+; VRAM word if that image should be positioned at X = (array_index % 16).
+WORD_PUT_PATTERN label word
+	db 11111111b, 11111111b
+	db 01111111b, 11111111b
+	db 00111111b, 11111111b
+	db 00011111b, 11111111b
+	db 00001111b, 11111111b
+	db 00000111b, 11111111b
+	db 00000011b, 11111111b
+	db 00000001b, 11111111b
+	db 00000000b, 11111111b
+	db 00000000b, 01111111b
+	db 00000000b, 00111111b
+	db 00000000b, 00011111b
+	db 00000000b, 00001111b
+	db 00000000b, 00000111b
+	db 00000000b, 00000011b
+	db 00000000b, 00000001b
diff --git a/th04_maine.asm b/th04_maine.asm
index f635de72..1b4dd541 100644
--- a/th04_maine.asm
+++ b/th04_maine.asm
@@ -1937,7 +1937,7 @@ loc_AEF1:
 		inc	ax
 		push	ax
 		push	0
-		call	sub_D078
+		call	_cdg_put_plane
 		mov	al, byte_124C7
 		add	al, 40h
 		mov	byte_124C7, al
@@ -1965,7 +1965,7 @@ loc_AEF1:
 		inc	ax
 		push	ax
 		push	1
-		call	sub_D078
+		call	_cdg_put_plane
 		mov	al, byte_124C7
 		add	al, 40h
 		mov	byte_124C7, al
@@ -1993,7 +1993,7 @@ loc_AEF1:
 		inc	ax
 		push	ax
 		push	2
-		call	sub_D078
+		call	_cdg_put_plane
 		mov	al, byte_124C7
 		add	al, 40h
 		mov	byte_124C7, al
@@ -2021,7 +2021,7 @@ loc_AEF1:
 		inc	ax
 		push	ax
 		push	3
-		call	sub_D078
+		call	_cdg_put_plane
 		mov	al, byte_124C7
 		add	al, 40h
 		mov	byte_124C7, al
@@ -2094,7 +2094,7 @@ loc_B04E:
 		inc	ax
 		push	ax
 		push	0
-		call	sub_D078
+		call	_cdg_put_plane
 		push	[bp+arg_4]
 		push	si
 		push	_CosTable8+128
@@ -2112,7 +2112,7 @@ loc_B04E:
 		inc	ax
 		push	ax
 		push	1
-		call	sub_D078
+		call	_cdg_put_plane
 		push	[bp+arg_4]
 		mov	ax, si
 		cwd
@@ -2138,7 +2138,7 @@ loc_B04E:
 		inc	ax
 		push	ax
 		push	2
-		call	sub_D078
+		call	_cdg_put_plane
 		push	[bp+arg_4]
 		push	si
 		push	_CosTable8+384
@@ -2156,7 +2156,7 @@ loc_B04E:
 		inc	ax
 		push	ax
 		push	3
-		call	sub_D078
+		call	_cdg_put_plane
 		mov	dx, 7Ch
 		mov	al, GC_OFF
 		out	dx, al
@@ -2226,7 +2226,7 @@ loc_B165:
 		inc	ax
 		push	ax
 		push	0
-		call	sub_D078
+		call	_cdg_put_plane
 		push	[bp+arg_4]
 		push	si
 		push	_CosTable8
@@ -2244,7 +2244,7 @@ loc_B165:
 		inc	ax
 		push	ax
 		push	1
-		call	sub_D078
+		call	_cdg_put_plane
 		push	[bp+arg_4]
 		mov	ax, si
 		cwd
@@ -2270,7 +2270,7 @@ loc_B165:
 		inc	ax
 		push	ax
 		push	2
-		call	sub_D078
+		call	_cdg_put_plane
 		push	[bp+arg_4]
 		push	si
 		push	_CosTable8+256
@@ -2288,7 +2288,7 @@ loc_B165:
 		inc	ax
 		push	ax
 		push	3
-		call	sub_D078
+		call	_cdg_put_plane
 		mov	dx, 7Ch
 		mov	al, GC_OFF
 		out	dx, al
@@ -5323,100 +5323,7 @@ sub_D046	endp
 
 ; ---------------------------------------------------------------------------
 		db    0
-
-; =============== S U B	R O U T	I N E =======================================
-
-; Attributes: bp-based frame
-
-; int __stdcall	__far sub_D078(int, int	slot, int, int)
-sub_D078	proc far
-
-arg_0		= word ptr  6
-@@slot		= word ptr  8
-arg_4		= word ptr  0Ah
-arg_6		= word ptr  0Ch
-
-		push	bp
-		mov	bp, sp
-		push	si
-		push	di
-		mov	si, [bp+@@slot]
-		shl	si, 4
-		add	si, 1B46h
-		mov	cx, [bp+arg_6]
-		mov	di, cx
-		sar	di, 4
-		shl	di, 1
-		add	di, [si+6]
-		mov	ax, [si+8]
-		shl	ax, 1
-		mov	byte ptr cs:loc_D0DC+1,	al
-		and	cx, 0Fh
-		mov	bx, cx
-		shl	bx, 1
-		mov	bx, [bx+580h]
-		mov	word ptr cs:loc_D0E3+1,	bx
-		mov	word ptr cs:loc_D0F0+1,	bx
-		jmp	short $+2
-		shl	ax, 1
-		add	ax, 50h	; 'P'
-		mov	dx, ax
-		mov	ax, [bp+arg_4]
-		mov	bx, ax
-		shl	ax, 2
-		add	ax, bx
-		add	ax, 0A800h
-		mov	es, ax
-		push	ds
-		mov	ax, [si+0Eh]
-		mov	si, [si]
-		mov	ds, ax
-		mov	ax, [bp+arg_0]
-		mov	bp, dx
-		mul	si
-		mov	si, ax
-		cld
-
-loc_D0DC:
-		mov	ch, 80h
-		lodsw
-		ror	ax, cl
-		mov	dx, ax
-
-loc_D0E3:
-		and	ax, 1234h
-		xor	dx, ax
-		stosw
-		dec	ch
-
-loc_D0EB:
-		lodsw
-		ror	ax, cl
-		mov	bx, ax
-
-loc_D0F0:
-		and	ax, 1234h
-		xor	bx, ax
-		or	ax, dx
-		mov	dx, bx
-		stosw
-		dec	ch
-		jnz	short loc_D0EB
-		or	dx, dx
-		jz	short loc_D107
-		mov	es:[di], dx
-		xor	dx, dx
-
-loc_D107:
-		sub	di, bp
-		jns	short loc_D0DC
-		pop	ds
-		pop	di
-		pop	si
-		pop	bp
-		retf	8
-sub_D078	endp
-
+include th04/formats/cdg_put_plane.asm
 include th04/snd/load.asm
 
 ; ---------------------------------------------------------------------------
@@ -5916,38 +5823,7 @@ include th02/formats/pfopen[data].asm
 include libs/master.lib/bgm_timerhook[data].asm
 include libs/master.lib/bgm[data].asm
 include th04/snd/se_priority[data].asm
-		db 0FFh
-		db 0FFh
-		db  7Fh
-		db 0FFh
-		db  3Fh	; ?
-		db 0FFh
-		db  1Fh
-		db 0FFh
-		db  0Fh
-		db 0FFh
-		db    7
-		db 0FFh
-		db    3
-		db 0FFh
-		db    1
-		db 0FFh
-		db    0
-		db 0FFh
-		db    0
-		db  7Fh
-		db    0
-		db  3Fh	; ?
-		db    0
-		db  1Fh
-		db    0
-		db  0Fh
-		db    0
-		db    7
-		db    0
-		db    3
-		db    0
-		db    1
+include th04/formats/cdg_put_plane[data].asm
 include th04/snd/snd[data].asm
 		db    0
 include th04/snd/load[data].asm