XDrawArc(3X11)

     NAME
          XDrawArc, XDrawArcs, XArc - draw arcs and arc structure

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

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

     ARGUMENTS
          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.

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

          x
          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.

     DESCRIPTION
          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+_____, y+ ______], and the
          infinitely thin path describing the entire circle or ellipse
          intersects the horizontal axis at [x, y+ ______] and
          [x+width, y+ ______] and intersects the vertical axis at
          [x+_____, y] and [x+_____, 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:

          skewed-angle = atan(tan(normal-angle)*______)+adjust

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

          0         for normal-angle in the range [0, _]
          J         for normal-angle in the range [_,  __]
          2J        for normal-angle in the range [ __, 2J]

          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.

     STRUCTURES
          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.

     DIAGNOSTICS
          BadDrawable
                    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.

     SEE ALSO
          XDrawLine(3X11), XDrawPoint(3X11), XDrawRectangle(3X11)
          Xlib - C Language X Interface