82 lines
2.5 KiB
QBasic
82 lines
2.5 KiB
QBasic
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REM These are the circle drawing functions.
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REM
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REM Use %INCLUDE CIRCOM.BAS to include the functions
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REM in your program.
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REM
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REM
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REM CALL BEG.CIR to initialize the circle arrays
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REM CALL PLOT.CIR to draw a circle without fill
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REM CALL FILL.CIR to draw a circle with fill
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REM
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REM The circle is centered at .5,.5 with a radius
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REM of .5 in a coordinate system ranging from 0 to 1
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REM on the X and Y axes.
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REM
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REM Initialize the circle drawing arrays X.ARRAY and
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REM Y.ARRAY by using CALL BEG.CIR in the beginning
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REM of your program. This statement only needs to
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REM be executed once. There is a long delay while
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REM this CALL is completed; you may want to put
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REM a message in your program to let the user know
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REM that the machine is computing.
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REM
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REM You can position the circle as you wish using
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REM the SET VIEWPORT and SET WINDOW statements prior
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REM to calling the drawing functions.
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REM
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REM The aspect ratio of the device must be adjusted
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REM in order to proportion the circle. You can use
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REM the following statements to accomplish this:
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REM
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REM ASK DEVICE X.AXIS,Y.AXIS
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REM SET WINDOW 0,X.AXIS/Y.AXIS,0,1
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REM
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REM These statements scale the window so that the X
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REM and Y axes use the same unit scaling regardless
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REM of the aspect ratio of the device. The circle
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REM is drawn with a shift to the left of the viewport
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REM because of the increased scaling of the X axis.
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REM You can also use the BOUNDS statement to square
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REM the device or the VIEWPORT statement to rescale
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REM the viewport.
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REM
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REM The functions make use of the variables L.CIR
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REM X.ARRAY, Y.ARRAY, and I.ANGLE. X.ARRAY is an
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REM array of the X coordinates of the points around
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REM the circle. Y.ARRAY is the corresponding Y
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REM coordinates. L.CIR contains a count of the
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REM number of coordinate pairs. I.ANGLE is only
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REM used by the FOR loop in BEG.CIR.
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REM
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DEF BEG.CIR
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DIM X.ARRAY(64)
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DIM Y.ARRAY(64)
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L.CIR=0
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REM THIS FOR LOOP STEPS THROUGH 0 TO 360 DEGREES
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REM USING RADIANS. THERE ARE 2PI RADIANS IN 360 DEGREES.
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FOR I.ANGLE = 0 TO 6.28 STEP .1
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X.ARRAY(L.CIR) = .5 + (.5 * COS(I.ANGLE))
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Y.ARRAY(L.CIR) = .5 + (.5 * SIN(I.ANGLE))
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L.CIR = L.CIR + 1
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NEXT I.ANGLE
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REM THE CIRCLE MUST BE CLOSED FOR MAT PLOT
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X.ARRAY(L.CIR) = X.ARRAY(0)
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Y.ARRAY(L.CIR) = Y.ARRAY(0)
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RETURN
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FEND
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DEF PLOT.CIR
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MAT PLOT L.CIR: X.ARRAY,Y.ARRAY
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RETURN
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FEND
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DEF FILL.CIR
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MAT FILL L.CIR-1: X.ARRAY,Y.ARRAY
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RETURN
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FEND
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