draw-ellipse-arc

Arguments: stream center semi-major-axis semi-minor-axis semi-major-axis-angle start-angle length-angle

Draws an ellipse arc on stream. The ellipse is defined by the center (a position) and the two half-axes, lengths from the center to the farthest point on the edge and to the nearest point on the edge, called the semi-major-axis and the semi-minor-axis. (Technically, the major axis should be longer than the minor axis but the two arguments need not have that relationship.) Because the Windows ellipse drawer can only draw ellipses that are vertically or horizontally oriented, the semi-major-axis-angle argument must be a multiple of 90. Other values will signal an error. The argument specifies the angle between the semi-major-axis and a line parallel to the x-axis passing through the center.

Angles are measured in degrees clockwise from the 3 o'clock position. The endpoint coordinates may be determined by calling ellipse-start-and-end.

So, the ellipse created when specifying semi-major-axis 200, semi-minor-axis 10, and semi-major-axis-angle 90 is a long, thin ellipse, 400 pixels wide, with the long axis vertical, centered at center. Now, with a start-angle of 0 and a length-angle of 90, all of the ellipse in the lower right quadrant is drawn and no part is drawn in any other quadrant.

center should be a position (see make-position). stream should be a cg-stream.

See also cg-drawing.htm.

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Created 2010.1.21.