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 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 rec-
       tangle and two angles.  The center of the circle or ellipse is the cen-
       ter 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+w_i_d_t_h_,y+h_e_i_g_h_t_], and the infinitely
       thin path describing the entire circle or ellipse intersects the hori-
       zontal axis at [x,y+h_e_i_g_h_t_] and [x+width,y+h_e_i_g_h_t_] and intersects the
       vertical axis at [x+w_i_d_t_h_,y] and [x+w_i_d_t_h_,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 perpendic-
       ular 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 cir-
       cle/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 identi-
       cal).  The relationship between these angles and angles expressed in
       the normal coordinate system of the screen (as measured with a protrac-
       tor) is as follows:

       skewed-angle=atan(tan(normal-angle)*h_w<I>e_i<I>i_d<I>g_t<I>h_h<I>t_)+adjust

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

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

       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 end-
       point and an equivalent counterclockwise extent, except as it affects
       joins.

       If the last point in one arc coincides with the first point in the fol-
       lowing 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 hori-
       zontal 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.

       BadDrawable
                 A value for a Drawable argument does not name a defined Win-
                 dow or Pixmap.

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

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

X Version 11                     libX11 1.1.1                      XDrawArc(3)