Bonk's Adventure tile and tilemap format


Document rev 1.0
----------------



	Tile Compression
	----------------

		
			The first byte of the string is the header byte.

			If header > 00,

			Low nibble: each bit represents a bit plane.
			
			 1 = tile+mask data 
			 0 = no data(write $00 for that bitplane)

			 If a bit is set, then a single byte mask is read from the string. Up to
			 two masks are read per loop (since bitplanes are interleaved in vram).

			High nibble: each bit corresponds to a bit plane.
		
			 1 = if mask bit is 0, then use $00 for that row of 8 pixels.
			 0 = if mask bit is 0, then use $FF for that row of 8 pixels.


			If header = 00,

			$00 is written for all pixels of that tile. No tile data proceeds the
			header byte for current tile. Basically this writes a blank tile to
			vram.



			An example string of an compressed tile:

			FF,FE,FE,FE,FE,<7 bytes>,<7 bytes>,<7 bytes>,<7 bytes>

			The header signifies that there are 4 masks and a run length of zero
			will be used for all bit planes. $FE = 7 bytes of tile data and a run
			length of zero on the last row(8) for that plane.

			Another example:

			F7,FE,FE,FE,<7 bytes>,<7 bytes>,<7 bytes>

			There are only 3 masks and bitplanes of data. The last bitplane is
			padded to $00.


			Level 1: 
			$8C9A bank $4B ($56C9A in ROM)





	Table of block address and length
	---------------------------------

		
			Contains a 6 byte entry.

			Format: (byte) bank #, (word) logical address, (word) VRAM address,
			(byte) block length (num of tile entries).

			If bank # = $FF, then termintate array.


			Title screen:
			$CB46, $CB4C, $CB52

			Level 1:
			$CDF5, $CDFB, $CE01


			*Routine for decoding table and tiles: $C729(table) and $C77E (tiles)*






	Tilemap metatile table
	----------------------
 

		Level 1 is $8AB3 bank $19
		
		Level 1-2 is @ $4c61 bank $14.


		table format: 6 bytes long entries 

			first byte: is the tile type/attribute. Used for collision
			detection,etc. 00=walk through, 01=solid

			second byte: is the bank of tiles. N * $100 = vram tile number
			starting position.

			byte 3-6: are the four tiles used to make the 16x16 metatile. 
			since the value is only $00-FF, the value is added to the bank
			select byte. All four tiles must be from the same bank/group.

			
			Palette association is fixed per bank. One 16 color palette for
			each bank. There is a total of 3 banks; 1 through 3. All other
			values will point to garbage in vram (tilemap or sprites).


	

	Tilemap
	-------

		level 1 is $8dd4 bank $19. 

		tilemap format: 1 byte = 16x16 metatile

			The map layout is stored as columns instead of rows. 
			
			$8DD4-$8DE3 is the first column of metatiles from top to bottom
			for level 1.

			Screens are stored sequentially in 20x16 metatiles maps.

			Note: The beginning of the tilemap is a string of 5 bytes. I'm
			not sure what they are, but for level one they are all 00's.
			Each time a column is read, these 5 bytes are read first, then
			routine jumps to the column address. I think these values might
			be used as buffer or border, since the values 00 are run through
			the same metatile converion process.









	Please contact: 
	tomaitheous@pcedev.net for questions.