Ubuntu Manpage: XDrawArc, XDrawArcs, XArc - draw arcs and arc structure

Provided by: libx11-doc_1.6.9-2ubuntu1.6_all

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 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+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 horizontal 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 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)*h_we_ii_dg_th_ht_⎞⎠+adjust

The skewed-angle and normal-angle are expressed in radians (rather than in degrees scaled
--

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