XDrawArc(3X) XDrawArc(3X)
NAME
XDrawArc, XDrawArcs - draw arcs
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 a pointer to 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.
- 1 -
XDrawArc(3X) XDrawArc(3X)
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 h
oe
righ
in
t of
width ______
_____ ],
, y+
the major and minor axes is at [x+
and the infinitely thin path describing the en2
tire
2
circle or ellipse intersects thehe
hi
og
rh
it
zontal axis at
height ______
______ ] and intersects
] and [x+width, y+
[x, y+
width
_____ 2
2 , y] and
the vertical axis at [x+
width
_____ 2
, y+height]. These coordinates can be
[x+
fract2
ional 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:
width)
( ______
|+adjust
skewed-angle = atan|tan(normal-angle)*
)
(
height
The skewed-angle and normal-angle are expressed in radians
(rather than in degrees scaled by 64) in the range [0, 2π]
- 2 -
XDrawArc(3X) XDrawArc(3X)
π
π _
_ ] and
,
and where atan returns a value in the range [-
adjust is: 2
2
π
_
]
0 for normal-angle in the range [0,
3π
π __
_ 2 ]
,
π for normal-angle in the range [
3π
__ 2
2 , 2π]
2π for normal-angle in the range [
2
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.
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
- 3 -
XDrawArc(3X) XDrawArc(3X)
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 Programming Manual
- 4 -