(This is part two of the chronicle of my Retrochallenge 2016/01 submission, which is to port some classic Star Trek text games to the Mattel Aquarius. To jump to the beginning, go here.)
As with most of my Retrochallenge experiences, what I imagine I can accomplish in the first weekend requires the remainder of the month. So it has been with the no-frills port of the 1972 version of STTR1 to the Aquarius. My real goal is to extend a classic Star Trek text game to use Aquarius features such as color, sound, and hand controllers. But here we are halfway through January and I’m still just trying to get the original STTR1 game to run on the target platform.
As of the last several work sessions I have a foothold into the game and am able to play for a bit before encountering a mysterious syntax error at line number 1910. And torpedoes targeted towards Klingons instead say that I shouldn’t attack stars.
In this post I will enumerate the types of code changes I’ve had to make so far and provide some brief examples. At a high level there’s the trivial changes and, well, the non-trivial.
Trivial Changes
Printing Concatenated Strings
HP doesn’t require semicolons as concatenation operators.
HP Time-Shared BASIC
1580 PRINT "YOU HAVE"E" UNITS OF ENERGY"
Aquarius BASIC
1580 PRINT "YOU HAVE";E;" UNITS OF ENERGY"
Array Indexes
HP uses square brackets. Aquarius uses parentheses.
HP Time-Shared BASIC
1630 D[I]=D[I]+1
Aquarius BASIC
1630 D(I)=D(I)+1
Chained Variable Assignments
HP allows chained assignments, the Aquarius does not.
HP Time-Shared BASIC
320 E0=E=3000 330 P0=P=10
Aquarius BASIC
320 E0=3000:E=E0 330 P0=10:P=P0
Shortening Command Lines to 72 Characters
Aquarius BASIC has a maximum line length of 72 characters. The original STTR1 source for the HP contains many, many lines that exceed that limit. These are simple but somewhat tedious changes.
Reformatting Output for a 40 Character Display
The teletype terminals that would be connected to an HP2000C had generous line widths for displaying the program output. The 40 character display on a television set requires inserting line breaks into the original STTR1 text.
HP Time-Shared BASIC
3690 PRINT USING 3700;K[I,1],K[I,2] 3700 IMAGE "KLINGON AT SECTOR ",D,",",D," DESTROYED ****"
Aquarius BASIC
3690 PRINT "KLINGON AT SECTOR ";K(I,1);",";K(I,2); 3700 PRINT " DESTROYED ****"
Formatted Output
HP Time-Shared BASIC provides formatted printing akin to C’s printf() function. IMAGE statements define a mix of literal strings and placeholders with format codes. The PRINT USING statement points to the line containing the desired IMAGE statement and a list of variables to be substituted for the placeholders.
HP Time-Shared BASIC
2720 PRINT USING 2730;H,K[I,1],K[I,2],K[I,3]
2730 IMAGE 4D," UNIT HIT ON KLINGON AT SECTOR ",D,",",D," (",3D," LEFT)"
Aquarius BASIC
2720 PRINT H;" UNIT HIT ON KLINGON":PRINT " AT SECTOR ";
2730 PRINT K(I,1);",";K(I,2);" (";K(I,3);" LEFT)":PRINT
Zeroing an Array
The HP has strong matrix support and has the ability to operate on all elements in a matrix with one command.
HP Time-Shared BASIC
260 DIM G[8,8],C[9,2],K[3,3],N[3],Z[8,8] ... 910 MAT K=ZER
Aquarius BASIC
260 DIM G(8,8),C(9,2),K(3,3),N(3),Z(8,8) ... 910 FOR I=0 TO 3:FOR J=0 TO 3:K(I,J)=0:NEXT J:NEXT I
Jumped GOTO
HP Time-Shared BASIC provides a variation of the ON x GOTO line1 line2… seen in other BASICs on micros but not found on the Aquarius. And…Was GOTO originally intended to be GO TO (two words)!?
HP Time-Shared BASIC
1270 PRINT "COMMAND:"; 1280 INPUT A 1290 GOTO A+1 OF 1410,1260,2330,2530,2800,3460,3560,4630
Aquarius BASIC
1270 PRINT "COMMAND:"; 1280 INPUT A 1290 IF A=0 THEN 1410 1292 IF A=1 THEN 1260 1293 IF A=2 THEN 2330 1294 IF A=3 THEN 2530 1295 IF A=4 THEN 2800 1296 IF A=5 THEN 3460 1297 IF A=6 THEN 3560 1298 IF A=7 THEN 4630
Non-Trivial Changes
Fundamental Differences in String Variables
HP Time-Shared BASIC
HP BASIC strings are implemented as a one-dimensional array of bytes. The command DIM S$ [n] reserves n bytes for string S$.
Throughout the original STTR1 code, much of the game’s “graphical” representation is accomplished by injecting the symbols for the Enterprise (‘<*>’), stars (‘ * ‘), and Klingons (‘+++’) into large strings, exploiting HP’s treatment of Strings as special cases of matrices.
However, HP BASIC strings are limited to 72 characters. For this reason, the young Mr. Mayfield had to split the 192 (8 x 8 x 3) characters needed to represent the Short Range Scan view across 3 string variables Q$, R$, and S$. And then add code to cascade across the variables when trying to inspect a particular spot in a quadrant.
Strings ---------------------------------
Q$[01-24]: * <*>
Q$[25-48]:
Q$[49-72]:
R$[01-24]: * *
R$[25-48]: * * *
R$[49-72]:
S$[01-25]: *
S$[01-48]:
---------------------------------
COMMAND:?
270 DIM C$[6],D$[72],E$[24],A$[3],Q$[72],R$[72],S$[48] ... 980 A$="<*>" ... 5510 REM ****** INSERTION IN STRING ARRAY FOR QUADRANT ****** 5520 S8=Z1*24+Z2*3-26 (Note: Z1 and Z2 are values between 1 and 8) 5530 IF S8>72 THEN 5560 5540 Q$[S8,S8+2]=A$ 5550 GOTO 5600 5560 IF S8>144 THEN 5590 5570 R$[S8-72,S8-70]=A$ 5580 GOTO 5600 5590 S$[S8-144,S8-142]=A$ 5600 RETURN
Aquarius BASIC
Strings do not need to be declared before use. The command DIM Q$ (64) creates an array of 64 (maybe 65) strings. For the Aquarius version of STTR1, strings will need to be used in a totally different way. Since the game’s “graphics” are stored as 3-character strings, I’ve opted to create an array of strings. In a 8×8 quadrant, Q$ will provide (64) 3-character strings.
270 DIM Q$(64) ... 980 A$="<*>" ... 5510 REM ****** INSERTION IN STRING ARRAY FOR QUADRANT ****** 5520 S8=(Z1-1)*8+Z2 (Note: Z1 and Z2 are values between 1 and 8) 5540 Q$(S8)=A$ 5600 RETURN
Memory
The target platform is an Aquarius with 16K RAM. If I drop the STTR1 code into an Aquarius emulator, FRE(0) shows that 1K of RAM is remaining. If I want to add new features, then the existing program will need to be put on a diet. Otherwise OM (Out of Memory) errors will begin to appear.
Solutions include: moving the embedded instructions to a separate, stand-alone program, combining multiple BASIC commands onto a single line, and creating an array of resource strings to use in place of repeated literals, like “KLINGON”, “TORPEDO”, and “ENTERPRISE”.
Up Next
Documenting the important variables used in STTR1.
16kram 