This is my attempt to describe how the PC versions of the SAGA images were formed. Note
I have taken this information from only a few games (the few PC ones I've been able to find).
If you have any PC 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:
The PC games are stored directly on a disc using separate files for each major part
of the game. These include the compiled interpreter, the SAGA+ datafile and the images.
The images have a file name which includes the name and number of the image, for example
B001.PAK - this indicates that it is used to overlay onto the room images and that it is
image number 1. The indicators are:
- B - signifies an overlay to an illustration
- R - signifies a room illustration
- S - signifies a programatically shown illustration, e.g. an illustration from EXAMining
Fortunately the file format is the same for each type of image. The files are drawn on
a basic CGA screen. This limits the graphics to only using 4 colours: black, cyan, magenta
and white. The screen resolution is 320 x 200.
Assuming that origin is at the top left of the screen. The area used for images starts
at (24,0) and extends to (204,158). This leaves a miniscule space of screen of 4 lines
for text descriptions!
|0x05||0x0d||Size of graphics chunk low byte|
|0x06||0x17||Size of graphics chunk high byte|
|0x07||0x0d||Size of graphics chunk low byte (repeat)|
|0x08||0x17||Size of graphics chunk high byte (repeat)|
|0x0d||0x00||Size flag (see below)|
|0x0e||0x00||Size flag (see below)|
|0x0f||0x06||Offset low byte|
|0x10||0x00||Offset high byte|
|0x11||0xac||Y length low byte|
|0x12||0x18||Y length high byte|
|0x13||0x46||X length low byte|
|0x14||0x00||X length high byte|
The Graphics Chunk
This is followed by the graphics chunk. The graphics are rended by a simple RLE encoding
If byte has bit 8 set
plot next byte (byte & 0x7f) times
plot the next byte (byte & 0x7f) times
Note, due to the low amount of colours, the graphics data is set at 2 bits per pixel with the
bit values being:
One final thing to note about how the plotting: the y-axis is interlaced; so row 0 is followed
by row 2; then row 158 is followed by row 1.
Also, note the offset and lengths are signified in block offsets including the
Complex images are formed by overlay other images over a basic image. For example, the
inventory in Sorcerer is formed by plotting the image R033 and then overlaying the B images (e.g.
B009, B023) over the top for each object in the inventory.
There is an extra form of compression, over the normal RLE encoding. On some images (most
of those in QP3!) the size of the horizontal pixels are doubled. This quarters the storage size
of the image; but lowers the quality.
This is signified by setting either or both 0x0d or 0x0e in the header to the value 0xff.
To render this simply double plot all X co-ordinates.
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 with the input filename, but with a .bmp
The extracted images:
Sorcerer of Claymorgue Castle
The Human Torch and The Thing