In Knight Lore and Alien 8 all background objects take up 1 byte. This byte simply states what background item it is. A further lookup table is used to to describe the background items location, graphic, etc.

The first background item for room 0 in Knight Lore is 0x00. Using the memory locations to the right (and finding it in the disassembly file) you can see that background type 0 is an arch to the north.

Looking at all the background bytes for room 0 it shows that this room has an arch to the north, an arch to the east and a wall size 0.

These were found as follows: look in the disassembly of Knight Lore for location 6ce2, this shows each of the background items with a description. How they are determined and the positions, etc are found by the 'DW'. Background type 0 (arch north) has a DW of 6D12h. If you look a bit further down the file you will location 6D12, this describes the background item in detail.

The format of the background data is complicated but it is as follows:

Background items can consist of more than one sprite (e.g. a door is two sprites). Bytes 0 to 6 determine the sprite number, position (x,y,z) and size; byte 7 contains various bit flags.

Repeat this block of 8 bytes until the sprite number byte is '0'. This signifies the end. If you look at the data you will see that the first background item (arch east) consists of two sprites.

The x, y, z locations of background items are in pixels.

Not all this data is strictly necessary if your aim is to simply extract the data to make a game. If you look in the map file you will see a section enclosed in comments that say, 'START OF BACKGROUND DATA UNTIL END'. This is the (useful) data extracted from the background - it is not a direct copy of bytes as in the location data because I require extra information to make the data useful within the viewer and export files.

Hopefully you have been looking at the background data for Knight Lore or Alien 8, as Pentagram is different!

Basically, the backgrounds in Pentagram use two bytes per item not one. The first byte is the background number and works exactly as the other games; the second byte (more often than not 0) is the room to jump to when the player exits the room via this object. Why?

If you remember from earlier, Alien 8 and Knight Lore are based on a map grid of 16x16 rooms, so going north from room 10 takes you to 10+16, which is 16. Pentagram does not do this (because rooms can be on top of others). So this byte is used instead. Really wasteful you have to admit, but then that's one of the many reasons to suggest Ultimate did not actually make this game!