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XDrawArc(3X11)


X11R6


NAME

  XDrawArc, XDrawArcs, XArc - draw arcs and arc structure


SYNOPSIS

  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+{width/2}, y+{height/2} ], and the
  infinitely thin path describing the entire circle or ellipse intersects the
  horizontal axis at [ x, y+{height/2} ] and [ x+width, y+{height/2} ] and
  intersects the vertical axis at [ x+{width/2 }, y ] and [ x+{width/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:

       skewed_angle \= atan [ tan(normal_angle) * (width/height) ] + adjust

  The skewed_angle and normal_angle are expressed in radians (rather than in
  degrees scaled by 64) in the range [ 0, 2pi ] and where atan returns a
  value in the range [ -pi/2, pi/2 ] and adjust is:

       0       for normal_angle in the range [ 0, pi/2 ]
       pi      for normal_angle in the range [ pi/2, 3pi/2 ]
       2pi     for normal_angle in the range [ 3pi/2, 2pi ]

  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

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