Manual pages › X Window and screen libraries (3X)

XDrArc(3X)

draw arcs

From the original Amiga UNIX 2.1 manual. Some things it mentions may not be in this release.

XDrawArc(3X11)                                     XDrawArc(3X11)

NAME

XDrawArc, XDrawArcs - draw arcs

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 a pointer to an array of arcs.

d Specifies the drawable.

display Specifies the connection to the XWIN 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

     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

XDrawArc(3X11)                                     XDrawArc(3X11)

     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 magni-
     tude 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 entire2circle or ellipse
                                              ______
     intersects the horizontal axis at [x, y+       ] and
                  ______                        2
     [x+width, y+       ] and intersects the vertical axis at
        _____       2    _____
     [x+     , y] and [x+     , y+height].  These coordinates can
     be fractional and so are not truncated to discrete coordi-
     nates.  The path should be defined by the ideal mathematical
     path. For a wide line with line-width lw, the bounding out-
     lines 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:
                        (                   width)
     skewed-angle = atan|tan(normal-angle)*______|+adjust
                        (                  height)

     The skewed-angle and normal-angle are expressed in radians
     (rather than in degrees scaled by 64) in the rJngJ      [0, 2J]
     and where atan returns a value in the range [-_, _] and
                                                   2  2
     adjust is:
                                                 J
     0         for normal-angle in the range [0, _]
                                              J         23J
     J        for normal-angle        in the range [_,  __]
                                              23J 2
     2J               for normal-angle        in the range [ __, 2J]
                                               2

XDrawArc(3X11)                                     XDrawArc(3X11)

     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 com-
     ponents: 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.

DIAGNOSTICS