GWBASIC User's Manual

GW-BASIC User's Guide
CIRCLE Statement
Purpose:
To draw a circle, ellipse, and angles on the screen during use of the Graphics mode.
Syntax:
CIRCLE(xcenter, ycenter), radius[,[color][,[start],[end][,aspect]]]
Comments:
xcenter and ycenter are the x- and y- coordinates of the center of the ellipse, and radius is
the radius (measured along the major axis) of the ellipse. The quantities xcenter and ycenter
can be expressions. The center attributes can use either absolute or relative coordinates.
color specifies the color of the ellipse. Its value depends on the current screen mode. See the
COLOR and SCREEN statements for more information on using colors in different screen
modes. In the high-resolution mode, 0 indicates black and 1 indicates white. The default for the
high resolution mode is 1.
The start and end angle parameters are radian arguments between -2π and 2π which specify
where the drawing of the ellipse is to begin and end. If start or end is negative, the ellipse is
connected to the center point with a line, and the angles are treated as if they are positive (note
that this is different from adding 2π).
aspect describes the ratio of the x radius to the y radius (x:y). The default aspect ratio depends
on the screen mode, but gives a visual circle in either graphics mode, assuming a standard
monitor screen aspect ratio of 4:3. If the aspect ratio is less than 1, then the radius is given in xpixels.
If it is greater than 1, the radius is given in y-pixels. In many cases, an aspect ratio of 1
gives better ellipses in the medium-resolution mode. This also causes the ellipse to be drawn
faster. The start angle may be less than the end angle.
Example 1:
10 SCREEN1: CIRCLE(100,100), 50
Draws a circle of radius 50, centered at graphics points 100x and 100y.
Example 2:
1 ' This will draw 17 ellipses
10 CLS
20 SCREEN 1
30 FOR R=160 TO 0 STEP-10
40 CIRCLE (160,100),R,,,,5/18
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