During the development stage of THE NEW ALADDIN, we investigated several graphic compression routines that were available for the Atari ST computer. While in certain cases one routine would work better than others, we found that in the long run TINYSTUF, a freeware program written by David Mumper of Sussex, Wisconsin, produced the smallest files. We had the program to compress our graphic files, but we could not find the source code that would allow our programs to expand the compressed files into full screen displays. Armed with a brief and, as I later found out, error-filled description of the compressed file and a file dump, I set out to develop a "C" subroutine to decompress TINY graphics files. First let me describe the com- pressed file. It is divided into three sections. The first section contains color information and the number of bytes in the other two sections. The second section contains control information which I will dis- cuss later, and the third, the data bytes for the picture. The first byte on the file tells you the resolution and whether ro- tation information follows. The values 0, 1, and 2 represent low, medium, and high resolution respec- tively, with 3 being added to indicate rotation. Next come the optional four bytes of rotation information. The first byte contains the start color in the high order four bits, while the end color is in the lower four. The second byte gives the direction and speed for the rotation. The value indicates the number of vertical blanks between each color shift. If the value is positive, the shift is to the right, while negative indicates a left shift of the colors. The next two bytes form an integer to indicate the number of rotations to be made. The color palette comes next and consists of 16 integers of two bytes each. This is followed by another two-byte integer that tells the number of control bytes for the file. Finally, there's another two-byte integer that tells how many two-byte pairs of graphic data are contained on the disk. The control bytes tell us how to format the data bytes. Their meaning is as follows: <0 -- 1 to 127 unique words (2 bytes) are taken from the data section. 0 -- the next two bytes in the control section tell how many times to repeat the next data word. 1 -- the next two bytes in the control section tell how many unique words are taken from the data section. >1 -- repeat the next data word 2 to 127 times. Now let's discuss how to use the routine in your "C" program. First we need to define some global variables. These are: long *screen_memory; int rez; int rotate [4]; int palette_array [16]; Allocate screen memory, which must be aligned on a 256-byte boundry with the instruction: screen_memory = (long *)((Malloc (32256L) + 255) & 0xffffff00); Then call the routine with: uncompress_graphic ("filename.ext", screen_memory, &rez, rotate, palette); The source code for the routine can be found on Aladdin disk "A" as DECOMP.C. TNYSTUFF and TINYVIEW, a slideshow program, can be found on many bulletin boards or through user groups. I wrote this routine in my early stages of learning "C" and the Atari ST. I am sure this isn't the most efficient way to attack this problem, but it works. If you have a better routine, let us hear about it and we'll share it with our readers. (Bo Davis is a systems analyst, the ST developer for THE NEW ALADDIN, and a Certified Data Processor.)
