XDrawArc(3)               XLIB FUNCTIONS              XDrawArc(3)



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

SYNTAX
       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);

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 rela-
                 tive 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 rela-
                 tive to the origin of the drawable and specify
                 the upper-left corner of the bounding rectangle.

DESCRIPTION
       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 speci-
       fied 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 tan-
       gent 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:

       l l.  %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 inter-
       sect, 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 counter-
       clockwise 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 cor-
       rectly.  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 hor-
       izontal or vertical line can be drawn.  Angles are com-
       puted 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 compo-
       nents: foreground, background, tile, stipple, tile-stip-
       ple-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 cor-
                 rect 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



X Version 11               libX11 1.1.5               XDrawArc(3)