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COMPUTER BITS BY RICK WALTERS Drawing circles in GW-Basic In the July 1996 issue, we discussed drawing borders on the screen using GW-Basic. This month, we will show you how to draw an analog clock on the screen. To draw circles, or for any acceptable current graphics, we need to use the highest resolution screen we can access. This is SCREEN 9 in GW Basic. Next we need to choose some colours that look effective. You can play around with the COLOR statement on line 1270 but be careful. Black on black is very hard to see! If we want to draw an analog clock face the first step is to draw a circle. This is done with the CIRCLE statement on line 2030. You will notice that we have not used numeric values for the circle centre and radius but values we have defined pre­viously in the INIT subroutine. 38  Silicon Chip As we will have to use these values again in the “update hands” subroutine, if we need to re-position the clock on the screen it is only necessary to change this one set of values on line 1080, rather than trying to find all the lines where the values were used. Perhaps we should elaborate on SCREEN 9 at this point. It consists of 640 x 350 pixels for drawing graphics but at the same time allows you to print text on an 80 x 25 grid. Thus, each character will occupy (640/80) = 8 pixels by (350/25) = 14 pixels. We can’t draw graphics on the 25th line, although we can place text there. Once we have drawn the circle and it looks about the right diameter, we have to calculate the position of each of the numbers which are placed every 30° around the circle. This is done using the formula on line 2050, which calculates the sine and cosine of the angle and locates the cursor at that point ready to print the number. So far we have a clock face, now for some hands. How do we know where to place them? PRINT TIME$ in Basic looks at the computer’s internal clock and prints this time, so if we use this function our clock will be as accurate as the computer’s is. Line 1260 dissects the time readout and defines the three parameters we are interested in: hours, minutes and seconds. By defining them as functions (DEF FN) they are available immediately; we don’t have to access the time and dissect it each time we need it. To synchronise the analog clock time to the computer we save the current second in line 3040 and wait until the next second begins. Initially there are no hands drawn, but once they are drawn they have to be erased and re-drawn every second. This is done in lines 3070-3120. To finish off we draw a couple of small circles at the centre of the face in line 3130. Right, you now have the bare bones clock which is capable of displaying and updating the time. If you want to improve it, add the individual minutes between the five minute marks and perhaps make the face a different colour to the surrounding screen. Look up your Basic manual for more information on color. Next time we will discuss sequential and random access files and the methods used for storing and retrievSC ing data. Listing 1 1 GOTO 10 2 GOSUB 1890: LPRINT TAB(55);” Printed on “;TODAY$ 1200 ULI = CHR$(195): DLI = CHR$(204): URI = CHR$(180): DRI = CHR$(185) 3 LLIST 1205 ‘Single & Double Left & Right intersections 4 END 1210 UTI = CHR$(194): DTI = CHR$(203): UBI = CHR$(193): DBI = CHR$(202) 5 SAVE “C:\clock”,A ‘Save file on C drive 6 SAVE “B:\clock”,A ‘Save file on B drive 7 END 10 REM Draw analog clock on screen 11 REM run 2 will print listing on printer 12 REM run 5 will save program to drive C 13 REM run 6 will save program to drive B (change to A if re­quired) 14 REM GOSUB 1900 Will clear from current cursor line to Line 24 20 GOSUB 1030 ‘Initialise 30 GOSUB 2030 ‘Draw face 40 GOSUB 3050 ‘Draw current time 50 GOSUB 3030 ‘Erase & update hands 1215 ‘Single & Double Top & Bottom intersections 1220 UCI = CHR$(197): DCI = CHR$(202) ‘Single & Double Centre intersection 1230 PI = 3.14159: BH = 8: RH = 4 ‘Black & red hands 1240 DEF FNS(X) = SIN (X * PI/180) ‘Define sine function from radians 1250 DEF FNC(X) = COS (X * PI/180) ‘Define cosine function from radians 1260 DEF FNHR$ = LEFT$(TIME$,2): DEF FNMIN$ = MID$(TIME$,4,2): DEF FNSEC$ = RIGHT$(TIME$,2) 1270 SCREEN 9: FC = 4: BC = 7: COLOR FC,BC ‘Fore & background 1280 YC = 175: XC = 325: RAD = 215 ‘Circle centre & radius 1890 TODAY$ = MID$(DATE$,4,2) + “-” + LEFT$(DATE$,2) + “-” + RIGHT$(DATE$,2) 60 LOCATE 25,1: PRINT FNCENTRE$(“Press SPACEBAR to return to DOS.”); 1899 RETURN 70 K = INKEY$: IF K < > “” THEN 999 1910 ‘Clear to end of screen subroutine. 80 GOTO 50 999 END’SYSTEM ‘Erase END’ when running OK 1000 ‘*********************** 1010 ‘Initialisation routine. 1020 ‘*********************** 1030 KEY OFF: DEFINT A-Z: DEFSTR D,E,K,U: DEFSNG P,S,C 1040 TODAY = VAL(MID$(DATE$,4,2)) 1050 ESC = CHR$(27): ENTER = CHR$(13): KSP = CHR$(32) ‘Spacebar 1060 KLA = CHR$(0) + CHR$(75): KRA = CHR$(0) + CHR$(77) ‘Left & right arrows 1070 KUA = CHR$(0) + CHR$(72): KDA = CHR$(0) + CHR$(80) ‘Up & down arrows 1080 KPU = CHR$(0) + CHR$(73): KPD = CHR$(0) + CHR$(81) ‘Page up & down 1090 KHOME = CHR$(0) + CHR$(71): KEND = CHR$(0) + CHR$(79) ‘Home & end 1100 DATA January, February, March, April, May, June, July 1110 DATA August, September, October, November, December 1120 DIM MONTH$(12): FOR A = 1 TO 12: READ A$: MONTH$(A) = A$: NEXT 1130 MONTH$ = MONTH$(VAL(LEFT$(DATE$,2))) ‘Current month 1140 DEF FNCENTRE$(M$) = SPACE$((79 - LEN(M$))/2) + M$ ‘Centre text 1150 DEF FNCEOL$ = STRING$(79 - POS(Q),” “) 1160 DEF FNYN = INSTR((“ YyNn”) + ENTER + ESC,INKEY$) 1165 ‘0 or 1, no key, 2 or 3 - Y, 4 or 5 - N, 6 - enter, 7 - escape 1170 ULT = CHR$(218): DLT = CHR$(201): URT = CHR$(191): DRT = CHR$(187) 1175 ‘Singe & Double Left & Right top corners 1180 ULB = CHR$(192): DLB = CHR$(200): URB = CHR$(217): DRB = CHR$(188) 1185 ‘Singe & Double Left & Right bottom corners 1190 UH = CHR$(196): DH = CHR$(205): UV = CHR$(179): DV = CHR$(186) 1195 ‘Single & Double Horizontal & vertical lines 1900 ‘********************************** 1920 ‘********************************** 1930 VIEW PRINT CSRLIN TO 24: CLS: VIEW PRINT 1999 RETURN 2000 ‘**************** 2010 ‘Draw clock face. 2020 ‘**************** 2030 CIRCLE (XC,YC),RAD ‘Draw circle centre XC,YC radius RAD 2040 FOR A = 1 TO 12 2050 LOCATE 13 - 10 * FNC(30 * A),40 + 24 * FNS(30 * A) ‘Cal­culate position 2060 PRINT A;: NEXT ‘write numbers 2099 RETURN 3000 ‘************* 3010 ‘Update hands. 3020 ‘************* 3030 OLDSEC = VAL(FNSEC$): OLDMIN = VAL(FNMIN$) + VAL(FNSEC$)/60:OLDHR = VAL(FNHR$) MOD 12 + VAL(FNMIN$)/60 3040 WHILE OLDSEC = VAL(FNSEC$): WEND ‘Wait for next second 3050 SEC = VAL(FNSEC$): MIN = VAL(FNMIN$) + VAL(FNSEC$)/60: HR = VAL(FNHR$) MOD 12 + VAL(FNMIN$)/60 3060 ‘ erase old hands, draw new ones 3070 LINE (XC,YC) - (XC + (180 * FNS(6 * OLDSEC)),YC - 130 * FNC(6 * OLDSEC)),BC 3080 LINE (XC,YC) - (XC + (180 * FNS(6 * SEC)),YC - 130 * FNC(6 * SEC)),RH 3090 LINE (XC,YC) - (XC + (172 * FNS(6 * OLDMIN)),YC - 126 * FNC(6 * OLDMIN)),BC 3100 LINE (XC,YC) - (XC + (172 * FNS(6 * MIN)),YC - 126 * FNC(6 * MIN)),BH 3110 LINE (XC,YC) - (XC + (154 * FNS(30 * OLDHR)),YC - 112 * FNC(30 * OLDHR)),BC 3120 LINE (XC,YC) - (XC + (154 * FNS(30 * HR)),YC - 112 * FNC(30 * HR)),BH 3130 FOR A = 1 TO 4: CIRCLE (XC,YC),A: NEXT 3199 RETURN January 1997  39