GETPUT

Developer(s): Michael DiRienzo
Date: 198x
Type: Program
Platform(s): TS 2068
Tags: Graphics

Demonstrates a pair of machine code routines that copy a rectangular block of the screen into memory (GET) and print it back anywhere (PUT). The demo draws a starburst with a single DRAW 57,10,4000 arc, grabs a 10×10 character block containing it, and bounces the block around the screen, beeping at each wall. The routines read their parameters from a PRINT statement that follows the call on the same line, RANDOMIZE USR get: PRINT AT row,col;width,height,address, so a call reads like ordinary BASIC. Here the block is stored at 50000.

The REM in line 1 reads “program “GETPUT” by michael DiRienzo”. Michael DiRienzo also wrote the graphics program Pix-Fx.

Program Analysis

Structure

  • Lines 5–45: set the colours, give the two entry points (get=60000, put=60006), draw the starburst, GET it, then show a flashing title and wait for a key.
  • Lines 50–100: the bounce loop. d=-1 is used to reverse dx and dy, and a PUT at y,x runs each pass.
  • Lines 9800–9900: loader. It does CLEAR 49999, POKEs 397 bytes into 60000–60396, checks they total 47831, and then RUNs the demo.

Machine Code

Both entry points set a flag at 60299 (0 for GET, 1 for PUT) and share the same code. It reads the rest of the BASIC line itself: it checks for :, the PRINT token and AT, evaluates the numbers through the ROM, and increments the statement counter (SUBPPC, INC (IY+13)) so BASIC skips the PRINT. It checks that the block fits on the screen and reports an error otherwise. It also appears to save the print-position and colour system variables along with the block, and to convert display-file addresses to attribute addresses, so colours seem to be copied as well as pixels.

Notable Techniques

  • The machine code takes its parameters from a dummy PRINT AT statement rather than from POKEs or DEF FN.
  • The loader checks the DATA against a checksum before running the demo. The 397 values in the listing do total 47831.
  • Because the program was saved with LINE 9000 and there is no line 9000, it starts at the first line after it, the loader at 9800.
  • Because the grabbed block includes a blank margin, moving it one character at a time wipes out its own trail.
  • Lines 49 and 89 are earlier versions left in as REMs.

This copy comes from a Larken disk. For tape, the RANDOMIZE USR 100 calls were removed from the save line, the Larken load line was emptied to a REM, and the program now autostarts at the loader. It was tested in ZEsarUX.

Related Articles

Here are two commands found in other computer BASICs which are missing from Sinclair BASIC.
Here are two commands found in other computer BASICs which are missing from Sinclair BASIC.
Please refer to the June issue of THE PLOTTER for details of this program.

Image Gallery

Source Code

    1 REM program "GETPUT"by michael DiRienzo
    5 INK 9: PAPER 7: BORDER 7: CLS 
   10 LET get=60000
   20 LET put=60006
   30 PLOT 9,142: DRAW 57,10,4000
   40 RANDOMIZE USR get: PRINT AT 0,0;10,10,50000
   45 PRINT FLASH 1;AT 4,2; INK 2;"GETPUT"; INVERSE 1;AT 5,2; INK 1;"Demo!!": PRINT AT 10,5; INK 9;"Press a key to start...": PAUSE 0
   49 REM RANDOMIZE USR get: PRINT AT 0,0;10,10,50000
   50 LET d=-1: LET dx=d: LET dy=d: LET x=-d: LET y=-d
   60 LET x=x+dx: LET y=y+dy
   70 IF NOT x OR x=22 THEN LET dx=dx*d: BEEP .01,y
   80 IF NOT y OR y=14 THEN LET dy=dy*d: BEEP .01,x
   89 REM PAUSE 10
   90 RANDOMIZE USR put: PRINT AT y,x;10,10,50000
  100 GO TO 60
 9800 CLEAR 49999: LET t=0
 9810 FOR n=60000 TO 60396
 9820 READ a: POKE n,a: LET t=t+a
 9830 NEXT n: IF t<>47831 THEN PRINT "Data Error! Recheck DATA lines": STOP 
 9840 RUN 
 9850 DATA 175,50,139,235,24,5,62,1,50,139,235,33,0,0,34,131,235,62,2,205,48,18,205,136,8,223,254,58,32,47,231,254,245,32,42,253,52,13,231,254,172,32,34,205,220,27,205,96,38,97,104,34,131,235,223,254,59,32,18,205,220,27,205,96,38,120,65,79,237,67,133,235,223,254,44,40,2,207,11,205,228,27,205,96,49,237,67,135,235,237,75,133,235,237,91,131,235
 9860 DATA 58,143,92,245,120,130,56,12,254,25,48,8,121,131,56,4,254,33,56,2,207,4,197,213,17,9,0,98,104,205,182,46,89,205,182,46,30,13,25,34,137,235,68,77,42,135,235,113,35,112,35,237,91,132,92,115,35,114,35,237,91,136,92,115,35,114,35,237,91,141,92,115
 9870 DATA 35,114,35,58,145,92,119,35,62,2,229,205,48,18,225,193,229,205,178,5,235,225,115,35,114,35,193,113,35,112,35,235,58,139,235,254,1,40,92,241,229,111,38,0,34,141,92,34,143,92,253,116,87,225,120,6,0,245,135,135,135,229,229,197
 9880 DATA 237,176,193,225,205,112,235,61,32,244,225,205,102,235,241,197,229,237,176,225,1,32,0,9,193,61,32,243,201,124,230,56,31,31,31,246,88,103,201,245,36,124,230,7,32,10,125,198,32,111,56,4,124,214,8,103,241,201,0,0,0,0,0
 9890 DATA 0,0,0,0,42,135,235,78,35,70,197,35,241,229,94,35,86,35,237,83,132,92,94,35,86,35,237,83,136,92,94,35,86,35,237,83,141,92,237,83,143,92,126,35,50,145,92,94,35,86,35,78,35,6,0,126,35,245,135
 9900 DATA 135,135,213,213,197,237,176,193,209,235,205,112,235,235,61,32,242,209,235,205,102,235,235,241,197,213,237,176,227,1,32,0,9,235,225,193,61,32,241,225,193,201
 9992 RANDOMIZE USR 100: SAVE "GETPUT.B1" LINE 9000
 9998 RANDOMIZE USR 100: LOAD "L.B1"

Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.

Tags

Archived Media Downloadable TS 2068 Graphics