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Tip of the Day
Language: Visual Basic
Expertise: Beginner
Aug 6, 1997

How to Calculate the X, Y of any Position on a Circle

The DegreesToXYsubroutine, part of CodeBank's standard procedure library, calculates the X (horizontal) and Y (vertical) coordinates of any point, measured in degrees, on the circumference of a circle or ellipse. As you can see, it's a pretty simple routine, but extremely valuable when drawing graphics or placing objects:

 
Public Sub DegreesToXY(CenterX As _
        Long, CenterY As Long, degree _
        As Double, radiusX As Long, _
        radiusY As Long, X As Long, Y _
        As Long)
Dim convert As Double
        convert = 3.141593 / 180 
        'pi divided by 180
        X = CenterX - (Sin(-degree * _
                convert) * radiusX)
        Y = CenterY - (Sin((90 + _
                (degree)) * convert) * radiusY)
End Sub




Pass the subroutine the center X, Y of your ellipse, the degree position, and the horizontal and vertical radii (if they are equal, you're specifying a circle, if not, it is an elongated ellipse). DegreesToXY will return the coordinates in the X and Y parameters. This routine has any number of uses, limited only by your imagination. For example, various CodeBank routines rely on it when drawing arched and rotated text, triangles, polygons, and jagged "smash" ovals when implementing motion effects, and much more.

Ward Hitt
 
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