PLOT, DRAW AND CIRCLE ROUTINE

by Lawrence Simons

Regular readers of these pages will remember Lawrence Simons' Plot routine published in issue 23 (August 88). Springing from those lines of DATA have come such popular programs as Spirographix and Mandelbrot. Other readers have had hours of enjoyment from a version of Mallard Basic, augmented by Plot, which can create some pretty stunning graphics. Unfortunately for newer readers that issue has now sold out.

However, new converts to Basic on the PCW should not fear, as the next few pages contain an updated, and far more versatile, version of this old favourite. Instead of just the plot routine, there are now built-in routines for line and circle drawing.

The Plot Routine is the brain of this listing. What it does is toggle on or off the pixels (if you look closely at your screen you can see the pixels that make up the letters). Draw and Circle enable you to create lines and circles using just two sets of coordinates. In order to achieve anything on the screen, you need to supply the routines with variables. All of these variables must be in integer form. A numeric variable is an integer when the % sign is at the end - for example circup%. The syntax and variables for each routine are explained below:

PLOT(X%,Y%,F%)
X% which must be between and 719.
Y% which must be between and 255.
These tell Plot where to begin on the screen. So X%=0 and Y%=0 would be at the bottom left of the screen.
The last one is F%: you can have one of three settings for this: 1 will Plot a pixel, 0 will Unplot (erase) a pixel. Any other integer will turn a green pixel black and vice versa (toggle).

10 REM MAKE BUBBLES                                                                    095C
20 GOSUB 60000                                                                         05EE
30 B$=CHRS(27):CL$=ES+"H"+E$+"E"                                                       0941
40 PRINT CL$;E$+"f"                                                                    0762
50 A%=2                                                                                0223
60 FOR i=5 TO 30                                                                       0688
70 R%=i:X%=RND*720:Y%=RND*255+i:F%=A%                                                  0F78
80 CALL CIRCLE(X%,Y%,R%,F%)                                                            0B2F
90 IF i>100 AND i< 110 THEN A%=0 ELSE A%=2                                             103C
100 NEXT i                                                                             0464
110 PRINT E$+"e"                                                                       062D
120 END                                                                                0361

Note the GOSUB 60000 in line 20. The rest of the section actually makes the bubbles. Lines 70 and 80 set up the integer variables and then calls the Circle routine.

60000 REM PLOT, DRAW & CIRCLE ROUTINES                                                 1270
60010 IF HIMEM<>62981! THEN ERROR 7                                                    0E2F
60020 MEMORY &HF2FF:E=0:a=HIMEM+1:RESTORE 60100                                        15E4
60030 PLOT=a:DRAW=a+3:CIRCLE=a+6                                                       0EB0
60040 RET=a+9:X0=a+10:Y0=a+12                                                          0A89
60050 FOR i=0 TO 41:c=0:F0R j=1 TO 16                                                  0E31
60051 READ x$:x=VAL("&H"+x$):c=c+x:POKE a,x:a=a+1:NEXT j                               1781
60070 READ x$                                                                          0494
60080 IF c<>VAL("&H"+x$) THEN E=E+1:PRINT "error in line";10*(i+6007)                  1DF5
60090 NEXT i:IF E=0  THEN RETURN ELSE PRINT E;"error(s)":ERROR 17                      1FA5

The beginning of the Circle Routine itself. Line 60010 ensures that the routine is loaded directly beneath the operating system. You may like to delele this line in order to load the routine elsewhere.

60100 DATA C3,30,F3,C3,B3,F3,C3,81,F4,FF,FF,FF,FF,FF,D9,C1,D1C                         16D2
60110 DATA 21,00,00,39,31,00,F6,E5,C5,21,09,F3,D9,4E,23,46,5D8                         1293
60120 DATA 78,B1,28,09,0B,78,B1,3E,01,28,02,3E,02,3C,08,C9,444                         12E1
60130 DATA E5,DD,E1,D5,FD,E1,60,69,CD,0E,F3,CD,41,F3,E1,F9,BC8                         15E8
60140 DATA C9,D9,36,01,D9,DD,4E,00,DD,46,01,FD,5E,00,FD,56,7AF                         1515
60150 DATA 01,ED,43,0A,F3,ED,53,0C,F3,21,CF,02,A7,ED,42,D8,80D                         157B
60160 DATA 7A,A7,37,C0,D9,36,00,D9,93,3D,5F,EB,F3,3E,81,D3,89F                         155D
60170 DATA F1,3C,D3,F2,29,11,00,B6,19,5E,23,56,EB,7D,E6,07,727                         1387
60180 DATA 5F,29,7D,E6,F0,B3,6F,59,79,E6,F8,4F,09,7B,E6,07,86D                         14E6
60190 DATA 3C,47,3E,01,0F,10,FD,08,47,08,10,05,2F,A6,77,18,3AE                         12DB
60200 DATA 08,10,04,B6,77,18,02,AE,77,3E,85,D3,F1,3C,D3,F2,710                         13B4
60210 DATA FB,A7,C9,E5,DD,E1,D5,FD,E1,60,69,CD,0E,F3,CD,C6,BEB                         1710

The very guts of the routine. The data which must be typed in commas and all. Try setting the cursor keys to numerics by pressing ALT and RELAY

60220 DATA F3,D9,71,E1,F9,C9,DD,6E,00,DD,66,01,ED,4B,0A,F3,9A4                         1594
60230 DATA A7,ED,42,EB,FD,6E,00,FD,66,01,ED,4B,0C,F3,A7,ED,95B                         169A
60240 DATA 42,D9,0E,02,D9,7A,B3,B4,B5,C8,0E,01,CB,7A,28,09,6E7                         1499
60250 DATA 0E,FF,7A,2F,57,7B,2F,5F,13,06,01,CB,7C,28,09,06,4AE                         14B3
60260 DATA FF,7C,2F,67,7D,2F,6F,23,ED,43,92,F5,A7,ED,52,38,824                         1471
60270 DATA 0C,19,ED,53,96,F5,22,98,F5,0E,00,18,0A,19,22,96,5A0                         1392
60280 DATA F5,ED,53,98,F5,06,00,ED,43,94,F5,2A,98,F5,44,4D,8C9                         1476
60290 DATA CB,3C,CB,1D,D9,0E,00,D9,C5,ED,4B,96,F5,09,ED,4B,878                         160B
60300 DATA 98,F5,A7,ED,42,38,06,ED,5B,92,F5,18,05,09,ED,5B,7DE                         1569
60310 DATA 94,F5,E5,2A,0A,F3,4B,7B,17,9F,47,09,DD,75,00,DD,790                         14BE

The same again and more. These are in fact the x$ which were read in lines 60051 and 60070.

60320 DATA 74,01,2A,0C,F3,4A,7A,17,9F,47,09,FD,75,00,FD,74,64B                         13EB
60330 DATA 01,CD,41,F3,D9,7E,B1,4F,D9,E1,C1,0B,78,B1,20,B8,8E0                         14C4
60340 DATA C9,E5,DD,E1,D5,FD,E1,60,69,5E,23,56,23,EB,4E,23,93E                         14D4
60350 DATA 46,ED,43,9E,F5,EB,5E,23,56,23,EB,CD,0E,F3,D9,36,8B6                         157E
60360 DATA 04,D9,2A,9E,F5,7C,A7,C0,D9,34,D9,B5,C8,CD,72,F5,A14                         1597
60370 DATA 22,A0,F5,2A,9E,F5,CD,81,F5,FD,6E,00,FD,66,01,22,8A8                         154B
60380 DATA 9C,F5,22,0C,F3,DD,6E,00,DD,66,01,22,9A,F5,09,22,71D                         1476
60390 DATA 0A,F3,D9,06,00,1E,01,D9,CD,FA,F4,D9,1C,7B,D9,FE,8D6                         1611
60400 DATA 05,38,F5,2A,9A,F5,DD,75,00,DD,74,01,2A,9C,F5,FD,847                         1443
60410 DATA 75,00,FD,74,01,D9,70,E1,F9,C9,3A,9E,F5,47,C5,05,8B1                         146A
60420 DATA D9,7B,D9,0F,38,05,3A,9E,F5,90,47,68,26,00,E5,CD,75D                         14AE
60430 DATA 72,F5,EB,2A,A0,F5,A7,ED,52,CD,5D,F5,EB,2A,9C,F5,ABC                         16FF

Even more of the same again. Just keep typing, the results will be well worth the effort.

Last but not least...even more data.

[BASIC listing with corrected line 60080] and [assembler listing]

DRAW (X%,Y%,F%)
Draw will create a straight line from the position of the last pixel plotted or drawn to the new coordinates. So in this case X% and Y% tell it where to finish the line. Their limits are the same as in Plot.

F% still has the same three settings as above. Draw, like the two other routines, will allow you to pass lines through anything else on screen and and will also 'undraw' itself. For example, you could create a pointer into some lextand then undraw it to give emphasis in a presentation.

CIRCLE(X%,Y%,R%,F%)
As you can see this has four variables, the R% being the odd one out. This stands for Radius and may be set at anything from 1 to 255. It cannot be zero for obvious reasons, you'd end up with an abstract circle and nothing on the screen to show off with!

Taken in combination, these routines will allow you to create some powerful visuals with which to impress and confound all those who doubt the PCW....and there are still a few lost souls!

In order to illustrate the Circle function, we have included lines 10 to 120 which create random 'bubbles' on the screen. When using any of the routines in your own programs you must first execute a GOSUB or GOTO to get to line 60000. This will invoke the routines and install them in high memory. In our Bubble example the code is installed by the CALL 60000; once all the numbers have been read and poked into memory the program returns from the installation subroutine and the bubbles are generated in lines 30 to 110. Line 120 ends the routine.

To use these new routines in your own programs you should delete lines 10-120 and save the remainder as DRAW.BAS or something similar. But don't forget any program you write using these routines must include the CALL 60000 as the first thing it does.

After all that, have fun and send us some examples!