CIRCLE - QB64 Wiki

CIRCLE

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The CIRCLE statement is used in graphics SCREEN modes to create circles, arcs or ellipses.


Syntax:

CIRCLE [STEP](Column, Row), radius%, [colour%][, startRadian!, stopRadian!] [, aspect!]


Parameters:

  • Can use STEP for relative coordinate moves from the previous graphic coordinates.
  • Coordinates designate the center position of the circle. Can be partially drawn offscreen.
  • radius% is an INTEGER value for half of the total circle diameter.
  • colour% is any available color attribute in the SCREEN mode used.
  • startRadian! and stopRadian! can be any SINGLE value from 0 to 2 * pi to create partial circles or ellipses.
  • aspect! SINGLE values of 0 to 1 affect the vertical height and values over 1 affect the horizontal width of an ellipse. Aspect = 1 is a normal circle.


Usage:

  • When using aspect! the startRadian! and stopRadian! commas MUST be included even if not used.
  • Radians move in a counter clockwise direction from 0 to 2 * Pi. Zero and 2 * Pi are the same circle radian at 3 o'clock.
  • Negative radian values can be used to draw lines from the end of an arc or partial ellipse to the circle center.
  • Commas after the colour% parameter are not required when creating a normal circle. Color can also be omitted.
  • The QB64 and QB graphic cursor is set to the center of the program window on program start for STEP relative coordinates.
  • CIRCLE can be used in any graphic screen mode, but cannot be used in the default screen mode 0 as it is text only!


Circle.BI Include file or SUB to use when using PAINT with pie charts or arc slices:

'CIRCLE.BI '** '** QB64 temporary replacement CIRCLE command. '** '** The CIRCLE command in QB64 has a few bugs listed below: '** '** - radian end points are not calculate properly when creating arcs '** - center line to radian end points do not close properly due to previous bug listed '** '** This circle command replacement works very similiarly to the native CIRCLE command: '** '** SYNTAX: CIRCLES x%, y%, radius!, color~&, start_radian!, end_radian!, aspect_ratio! '** '** x% - center X coordinate of circle '** y% - center Y coordinate of circle '** radius! - the radius of the circle '** color~& - the circle's color '** start_radian! - the radian on circle curcunference to begin drawing at '** end_radian! - the radian on circle circumference to end drawing at '** aspect_ratio! - the aspect ratio of the circle '** '** NOTE: unlike the native CIRCLE command, all arguments MUST be supplied. For example, '** with the native command this will draw a perfect circle with the default color, '** start radian, end radian and aspect ratio: '** '** CIRCLE (319, 239), 100 '** '** To do the same thing with this replacement command you must supply everything: '** '** CIRCLES 319, 239, 100, _RGB32(255, 255, 255), 0, 0, 0 '** '** ACKNOWLEGEMENTS: The FOR/NEXT step formula was was written by Codeguy for Unseen '** Machine's Visual library EllipseXS command. Specifically: '** MinStep! = 1 / (2 * 3.1415926535 * Radius!) '** '** '** Includes performance tweaks made by SMcNeill on 02/02/13 - specifically removing a few redundant * -1 '** statements and converting the FOR/NEXT loop to a DO loop for a ~3% increase in performance. '** '** Corrected bug in which variables being passed in were being modified and passed back - 02/02/13 '** SUB CIRCLES (cx%, cy%, r!, c~&, s!, e!, a!) DIM s%, e%, nx%, ny%, xr!, yr!, st!, en!, asp! ' local variables used st! = s! ' copy start radian to local variable en! = e! ' copy end radian to local variable asp! = a! ' copy aspect ratio to local variable IF asp! <= 0 THEN asp! = 1 ' keep aspect ratio between 0 and 4 IF asp! > 4 THEN asp! = 4 IF asp! < 1 THEN xr! = r! * asp! * 4 ELSE xr! = r! ' calculate x/y radius based on aspect ratio IF asp! > 1 THEN yr! = r! * asp! ELSE yr! = r! IF st! < 0 THEN s% = -1: st! = -st! ' remember if line needs drawn from center to start radian IF en! < 0 THEN e% = -1: en! = -en! ' remember if line needs drawn from center to end radian IF s% THEN ' draw line from center to start radian? nx% = cx% + xr! * COS(st!) ' yes, compute starting point on circle's circumference ny% = cy% + yr! * -SIN(st!) LINE (cx%, cy%)-(nx%, ny%), c~& ' draw line from center to radian END IF IF en! <= st! THEN en! = en! + 6.2831852 ' come back around to proper location (draw counterclockwise) stepp! = 0.159154945806 / r! c! = st! ' cycle from start radian to end radian DO nx% = cx% + xr! * COS(c!) ' compute next point on circle's circumfrerence ny% = cy% + yr! * -SIN(c!) PSET (nx%, ny%), c~& ' draw the point c! = c! + stepp! LOOP UNTIL c! >= en! IF e% THEN LINE -(cx%, cy%), c~& ' draw line from center to end radian if needed END SUB


Example 1: Finding when the mouse is inside of a circular area:

SCREEN 12 r& = 200 'radius change circle size and position here cx& = 320 'center x horizontal cy& = 240 'center y vertical DO i = _MOUSEINPUT x& = _MOUSEX y& = _MOUSEY xy& = ((x& - cx&) ^ 2) + ((y& - cy&) ^ 2) 'Pythagorean theorem IF r& ^ 2 >= xy& THEN CIRCLE (cx&, cy&), r&, 10 ELSE CIRCLE (cx&, cy&), r&, 12 LOOP UNTIL INKEY$ = CHR$(27) 'escape key exit

Explanation: The square of the circle radius will be greater than or equal to the sum of the square of the mouse coordinates minus the center position when the pointer is inside of the circle. In this example the circle color will change from red to green.


Example 2: Program illustrates how the CIRCLE command using a negative radian value can be used to create the hands of a clock.

CONST PI = 3.141593 'The mathematical value of PI to six places DIM clock(60) 'A dimensioned array to hold 60 radian points clockcount% = 15 'A counter to keep track of the radians '* Start at radian 2*PI and continue clockwise to radian 0 '* Since radian 2*PI points directly right, we need to start clockcount% '* at 15 (for 15 seconds). The FOR/NEXT loop counts backwards in increments '* of 60 giving us the 60 second clock points. These points are then stored '* in the dimensioned array clock() to be used later. '* FOR radian = 2 * PI TO 0 STEP -(2 * PI) / 60 clock(clockcount%) = radian clockcount% = clockcount% + 1 IF clockcount% = 61 THEN clockcount% = 1 NEXT radian '* Change to a graphics screen and draw the clock face SCREEN 7 CLS LOCATE 1, 1 COLOR 14, 0 PRINT "Ritchie's Clock" COLOR 9, 0 PRINT "Uses CIRCLE to" PRINT "draw hands!" COLOR 8, 0 CIRCLE (160, 100), 110, 8 'circle with radius of 110 and dark gray CIRCLE (160, 100), 102, 8 'circle with radius of 102 and dark gray PAINT (265, 100), 8, 8 'fill between the two dark gray circles with gray CIRCLE (160, 100), 110, 7 'circle with radius of 110 and light gray '* '* Get the current time from the QuickBASIC built in variable TIME$ '* Since TIME$ is a string, we need to extract the hours, minutes and '* seconds from it using LEFT$, RIGHT$ and MID$. Then, each of these '* extractions need to be converted to a numeric value using VAL and '* stored in their respective variables. '* seconds% = INT(VAL(RIGHT$(TIME$, 2))) 'extract seconds from TIME$ IF seconds% = 0 THEN seconds% = 60 'array counts 1 to 60 not 0 to 59 previoussecond% = seconds% 'hold current second for later use minutes% = INT(VAL(MID$(TIME$, 4, 2))) 'extract minutes from TIME$ IF minutes% = 0 THEN minutes% = 60 'array counts 1 to 60 not 0 to 59 previousminute% = minutes% 'hold current minute for later use hours% = INT(VAL(LEFT$(TIME$, 2))) 'extract hour from TIME$ IF hours% >= 12 THEN hours% = hours% - 12 'convert from military time IF hours% = 0 THEN hours% = 12 'count from 1 to 12 not 0 to 11 previoushour% = hours% 'hold current hour for later use '* '* Start of main program loop '* DO IF seconds% <> previoussecond% THEN 'has a second elapsed? LOCATE 22, 17 'print the time on the screen at PRINT TIME$; 'position 22, 17 '* Since a second has elapsed we need to erase the old second hand '* position and draw the new position CIRCLE (160, 100), 100, 0, -clock(previoussecond%), clock(previoussecond%) CIRCLE (160, 100), 100, 15, -clock(seconds%), clock(seconds%) previoussecond% = seconds% 'hold current second for later use IF minutes% <> previousminute% THEN 'has a minute elapsed? '* Since a minute has elapsed we need to erase the old hour hand position CIRCLE (160, 100), 90, 0, -clock(previousminute%), clock(previousminute%) previousminute% = minutes% 'hold current minute for later use END IF '* '* Draw the current minute hand position '* CIRCLE (160, 100), 90, 14, -clock(minutes%), clock(minutes%) IF hours% <> previoushour% THEN 'has an hour elapsed? '* Since an hour has elapsed we need to erase the old hour hand position CIRCLE (160, 100), 75, 0, -clock(previoushour% * 5), clock(previoushour% * 5) previoushour% = hours% 'hold current hour for later use END IF '* '* Draw the current hour hand position '* CIRCLE (160, 100), 75, 12, -clock(hours% * 5), clock(hours% * 5) END IF seconds% = VAL(RIGHT$(TIME$, 2)) 'extract time again and do all over IF seconds% = 0 THEN seconds% = 60 minutes% = VAL(MID$(TIME$, 4, 2)) IF minutes% = 0 THEN minutes% = 60 hours% = VAL(LEFT$(TIME$, 2)) IF hours% >= 12 THEN hours% = hours% - 12 IF hours% = 0 THEN hours% = 12 LOOP UNTIL INKEY$ <> "" 'stop program if user presses a key

Circle clock - by Terry Ritchie 11/04/06


See also:



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