*XDrawArc*
draws a single circular or elliptical arc, and
*XDrawArcs*
draws multiple circular or elliptical arcs.
Each arc is specified by a rectangle and two angles.
The center of the circle or ellipse is the center of the
rectangle, and the major and minor axes are specified by the width and height.
Positive angles indicate counterclockwise motion,
and negative angles indicate clockwise motion.
If the magnitude of angle2 is greater than 360 degrees,
*XDrawArc*
or
*XDrawArcs*
truncates it to 360 degrees.
For an arc specified as [ *x,* *y,* *width*, *height,* *angle1,* *angle2*],
the origin of the major and minor axes is at
[*x*+ *width* / 2, *y*+ *height* / 2],
and the infinitely thin path describing the entire circle or ellipse
intersects the horizontal axis at [*x,* *y*+ *height* / 2] and
[*x*+ *width*, *y*+ *height* / 2]
and intersects the vertical axis at [*x*+ *width* / 2, *y*] and
[*x*+ *width* / 2, *y*+ *height*].
These coordinates can be fractional
and so are not truncated to discrete coordinates.
The path should be defined by the ideal mathematical path.
For a wide line with line-width lw,
the bounding outlines for filling are given
by the two infinitely thin paths consisting of all points whose perpendicular
distance from the path of the circle/ellipse is equal to lw/2
(which may be a fractional value).
The cap-style and join-style are applied the same as for a line
corresponding to the tangent of the circle/ellipse at the endpoint.

For an arc specified as [ *x,* *y,* *width,* *height,* *angle1,* *angle2*],
the angles must be specified
in the effectively skewed coordinate system of the ellipse (for a
circle, the angles and coordinate systems are identical). The
relationship between these angles and angles expressed in the normal
coordinate system of the screen (as measured with a protractor) is as
follows:

`
roman "skewed-angle" ~ = ~ atan left ( tan ( roman "normal-angle" )
skewed-angle = `*atan*( tan (normal-angle)**width* / *height*)+ *adjust*

The skewed-angle and normal-angle are expressed in radians (rather
than in degrees scaled by 64) in the range [0, 2*pi*] and where atan
returns a value in the range [-*pi* / 2, *pi* / 2]
and adjust is:

0 | for normal-angle in the range [0, *pi* / 2] |

*pi* | for normal-angle in the range [*pi* / 2, 3*pi* / 2] |

2*pi* | for normal-angle in the range [3*pi* / 2, 2*pi*] |

For any given arc,
*XDrawArc*
and
*XDrawArcs*
do not draw a pixel more than once.
If two arcs join correctly and if the line-width is greater than zero
and the arcs intersect,
*XDrawArc*
and
*XDrawArcs*
do not draw a pixel more than once.
Otherwise,
the intersecting pixels of intersecting arcs are drawn multiple times.
Specifying an arc with one endpoint and a clockwise extent draws the same pixels
as specifying the other endpoint and an equivalent counterclockwise extent,
except as it affects joins.

If the last point in one arc coincides with the first point in the following
arc, the two arcs will join correctly.
If the first point in the first arc coincides with the last point in the last
arc, the two arcs will join correctly.
By specifying one axis to be zero, a horizontal or vertical line can be
drawn.
Angles are computed based solely on the coordinate system and ignore the
aspect ratio.

Both functions use these GC components:
function, plane-mask, line-width, line-style, cap-style, join-style,
fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin,
tile-stipple-y-origin, dash-offset, and dash-list.

*XDrawArc*
and
*XDrawArcs*
can generate
*BadDrawable*,
*BadGC*,
and
*BadMatch*
errors.