
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 threeo'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 draw
able and specify the upperleft 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+_____,y+______], and the infinitely thin path describing the entire
circle or ellipse intersects the horizontal axis at [x,y+______] and [x+width,y+______]
and intersects the vertical axis at [x+_____,y] and [x+_____,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 linewidth 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 capstyle and joinstyle 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:
skewedangle=atan(tan(normalangle)*______)+adjust
The skewedangle and normalangle are expressed in radians (rather than in degrees scaled
by 64) in the range [0,2n] and where atan returns a value in the range [_,_] and adjust
is:
l l. 0 for normalangle in the range [0,_] n for normalangle in the range [_,__]
2n for normalangle in the range [__,2n]
For any given arc, XDrawArc and XDrawArcs do not draw a pixel more than once. If two arcs
join correctly and if the linewidth 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, planemask, linewidth, linestyle, cap
style, joinstyle, fillstyle, subwindowmode, clipxorigin, clipyorigin, and clip
mask. They also use these GC modedependent components: foreground, background, tile,
stipple, tilestipplexorigin, tilestippleyorigin, dashoffset, and dashlist.
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 16bit unsigned
integers. You should be careful not to generate coordinates and sizes out of the 16bit
ranges, because the protocol only has 16bit 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
X Version 11 libX11 1.2.1 XDrawArc(3) 
