bcdfb–bcdfn — Monster Sprites

bcdfb–bcdfn — Monster Sprites

These 13 files (one per dungeon level, b = map 1 … n = map 13) hold that level’s monster graphics, wall decorations, and a sound bank. They’re opened by name from the decompressed bcdft image via a patched "bcdf?" template (S_1 +0x21E7E): filename letter = 0x62 + (level−1).

File structure

12-byte header
42 × 28-byte directory entries
214-byte raw table
one RLE stream from offset 1402

The RLE stream starts at byte 1402, not immediately after the directory — this was a long-standing decode bug. The 214 bytes between the directory and the stream are a raw table, not compressed data.

The directory entry (28 bytes)

Offset	Size	Field	Notes
+0	4	data_off	offset into the concatenated decompressed stream
+4	4	bpr	bytes per plane = (width/8) × total height
+8	4	reserved	0
+12	2	BLTSIZE	(height<<6) | (width/16 + 1)
+14	2	modulo	screen modulo
+16	4	reserved	0
+20	2	type	0x0100/0x0500 (frame variant)
+22	2	width	pixels
+24	2	height	total rows (sum of frame heights)
+26	2	reserved	0

204 sprites, not 546

Each file has 42 directory entries (546 across all 13 files) — but entries that share a data_off are a normal/mirrored pair of the same image, not separate animation frames. This yields 204 distinct sprites.

Sprite layout

Each sprite is 7 sequential planes — plane 0 is the 1-bit cookie-cut mask, planes 1–6 are the 6bpp EHB colour. Bit order is standard (plane 1 → bit 0).

plane_0 = raw[0 : bpr]            ; mask (1 = opaque)
plane_1 = raw[bpr : bpr*2]        ; colour bit 0 (LSB)
...
plane_6 = raw[bpr*6 : bpr*7]      ; colour bit 5 (EHB half-bright MSB)

Trailing data — wall decorations + sound

The 9–19 KB that follows each sprite stream splits at a fixed 1932-byte boundary:

• [0, 1932) = 3 wall decorations × 644 B, each holding the same object at three view distances (16×20 / 16×15 / 16×11, 7 sequential planes). These are the keyhole/lock plates, a red-cross panel, and a gargoyle face.
• [1932, EOF) = a raw signed-8-bit PCM sound bank, samples back to back. Verified against 8 DOS clipper.clp samples byte-for-byte.

Palette

Monsters share the single dungeon EHB palette — there is no separate monster palette. The half-bright (EHB) computation must happen on the 4-bit nibble, not the scaled 8-bit value:

correct:   half = (nibble >> 1) * 17
wrong:     half = (nibble * 17) // 2     # off by up to 8 per channel on odd nibbles

Extraction

scripts/extract_monsters.py → public/assets/blackcrypt/amiga/sprites/monsters.*