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       XDrawArc, XDrawArcs, XArc - draw arcs and arc structure


       int  XDrawArc(Display  *display,  Drawable  d,  GC  gc,  int x, int y, unsigned int width,
              unsigned int height, int angle1, int angle2);

       int XDrawArcs(Display *display, Drawable d, GC gc, XArc *arcs, int narcs);


       angle1    Specifies the start of the arc relative to the three-o'clock position  from  the
                 center, in units of degrees * 64.

       angle2    Specifies  the  path  and extent of the arc relative to the start of the arc, in
                 units of degrees * 64.

       arcs      Specifies an array of arcs.

       d         Specifies the drawable.

       display   Specifies the connection to the X server.

       gc        Specifies the GC.

       narcs     Specifies the number of arcs in the array.

       height    Specify the width and height, which are the major and minor axes of the arc.

       y         Specify the x and y coordinates,  which  are  relative  to  the  origin  of  the
                 drawable and specify the upper-left corner of the bounding rectangle.


       delim  %% 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 over 2} , ~y +^ {height over 2}  ]%, and
       the infinitely thin path describing the entire circle or ellipse intersects the horizontal
       axis  at  % [ x, ~y +^ {height over 2}  ]% and % [ x +^ width , ~y +^ { height over 2 }] %
       and intersects the vertical axis at % [ x +^ { width over 2 } , ~y ]% and % [ x +^ { width
       over  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" )
        * width over height right ) +^ 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
       over 2 , ~pi over 2  ] % and adjust is:

       %0%      for normal-angle in the range % [ 0 , ~pi over 2  ]%
       %pi%     for normal-angle in the range % [ pi over 2 , ~{3 pi} over 2  ]%
       %2 pi%   for normal-angle in the range % [ {3 pi} over 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.


       The XArc structure contains:

       typedef struct {
             short x, y;
             unsigned short width, height;
             short angle1, angle2;             /* Degrees * 64 */
       } XArc;

       All x and y members are signed integers.  The width and height members are 16-bit unsigned
       integers.  You should be careful not to generate coordinates and sizes out of  the  16-bit
       ranges, because the protocol only has 16-bit fields for these values.


                 A value for a Drawable argument does not name a defined Window or Pixmap.

       BadGC     A value for a GContext argument does not name a defined GContext.

       BadMatch  An InputOnly window is used as a Drawable.

       BadMatch  Some  argument  or pair of arguments has the correct type and range but fails to
                 match in some other way required by the request.


       XDrawLine(3), XDrawPoint(3), XDrawRectangle(3)
       Xlib - C Language X Interface