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Adventure International

Atari RLE
Gfx File Format


This is my attempt to describe how some of the Atari versions of the SAGA images were formed. Note, I have taken this information from only a few games (the few Atari ones I've been able to find). If you have any Atari versions of the other SAGA games I would like to see them so I can ensure that my routines work on all of them. The games I used are:

Basic format

The Atari games come on two discs, the first disc contains the machine code and the game data. The second disc just seems to contain graphic data, with a small initial boot sector to tell somebody booting from that disc to use the other disc.

The discs aren't read as files - just directly read from the disc; so we can treat the whole disc as a data file.

The files are drawn with a graphics resolution of 320 x 200. The Atari screen mode restricts colours to 5, but these can be allocated from a base of 128 different colours. White is always used for text and Black is always used for the background.

Assuming that origin is at the top left of the screen. The area used for images starts at (24,0) and extends to (304,159). This leaves a miniscule space of screen of 4 lines for text descriptions! On areas where the image is smaller than normal the text uses the extra lines.

The image data for the first image starts at 0x297, and the images follow sequentially.

The image data seems closely related to the PC image data.

The Header

0x000xfeSize of image low byte
0x010x05Size of image high byte
0x020x03Minimum X co-ordinate (in blocks of 8 pixels) (MinX)
0x030x00Minimum Y co-ordinate (MinY)
0x040x26Maximum X co-ordinate (in blocks of 8 pixels) (MaxX)
0x050x9eMaximum Y co-ordinate (MaxY)
0x060x0eColour for index 1
0x070x87Colour for index 2
0x080x0eColour for index 3
0x090x00Colour for index 0 (? - I've always seen it as 0x00)

Note, the size doesn't always seem to lead perfectly to the next image, you may have to skip 0x00 bytes until you reach the header!

The Graphics Chunk

This is followed by the graphics chunk. The graphics are rended by a simple RLE encoding scheme:

	  read byte
	  if byte has bit 7 set
		 read byte1, byte2
		 repeat ((byte & 0x7F) + 1) times
			plot byte1, byte2
		 repeat (byte + 1) times
			read byte1, byte2
			plot byte1, byte2

Note, due to the low amount of colours, the graphics data is set at 2 bits per pixel, with each two bits representing a colour index from 0 - 4. All the x pixel values are plotted twice. For example the value 0xa5 would be turn into eight pixels as:


To confuse issues, this version plots y first, rather than x. It always provides the next two y values after the encoding. So the plotting order is:

	  get byte1, byte2
	  plot byte1
	  increase y
	  plot byte2
	  if y > MaxY
		 y = MinY
		 increase x (in blocks of 8 pixels)

Stop plotting when the x offset (in blocks of 8 pixels) gets greater than maxX (in blocks of 8 pixels). Beyond this until the end of the graphics chunk the data is undefined.

Complex images are formed by overlaying other images over a basic image.


There are a couple of variations to the above format, both Voodoo Castle and The Count are in a slightly more basic format - bit 7 of the counter byte does nothing special - all counter bytes are treated as counters. Also, it matches the end of a column on y >= ylen.

Image 55 on The Count is corrupt on the discs I have, but doesn't seem to be used in the game.

The Sorcerer of Claymorgue Castle and The Hulk fill up the second disc totally, meaning that the image for the inventory is kept on the first disc at an index of 0x9890

Bytes 0xb390 to 0xb410 correspond to the content of sector 360 (0x0168) which contains the volume table of contents of the disk (mostly a bitmap of used sectors). This is not part of the graphics data and should be skipped. For the code below, this sector was edited out by hand with a hex editor.


The code is relatively simple to extract the images from the originals. Here is the C code I was using to test my extraction routines. It uses the allegro library and will save the image as Output<image>.bmp. The CLI parameters are:
arledraw <disc2 image> <offset> <num images> <version flag>

The version flag should be y for Voodoo Castle and The Count

You will also need a palette file. I stole this one from Atariwin :-)

Note the C is not very good and was evolved and hacked during my tests!


The extracted images:

Voodoo Castle
Voodoo Castle
The Count
The Count
Sorcerer of Claymorgue Castle
The Sorcerer of Claymorgue Castle
Buckaroo Banzai
Buckaroo Banzai in the Fifth Dimension
The Hulk
The Hulk
The Thing and The Human Torch
The Thing and The Human Torch