unixdev.net


Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (Debian-5.0)
Page:
Section:
Apropos / Subsearch:
optional field

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 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
       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 specified by the width and height.  Positive angles indicate coun-
       terclockwise 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 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 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 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.

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 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.

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



X Version 11                     libX11 1.1.5                      XDrawArc(3)