XDrawArc(3X11)XDrawArc(3X11)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
Specifies the start of the arc relative to the three-o'clock position
from the center, in units of degrees * 64. Specifies the path and
extent of the arc relative to the start of the arc, in units of degrees
* 64. Specifies an array of arcs. Specifies the drawable. Specifies
the connection to the X server. Specifies the GC. Specifies the num‐
ber of arcs in the array. Specify the width and height, which are the
major and minor axes of the arc. 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.
DESCRIPTIONXDrawArc draws a single circular or elliptical arc, and XDrawArcs draws
multiple circular or elliptical arcs. Each arc is specified by a rec‐
tangle and two angles. The center of the circle or ellipse is the cen‐
ter 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 frac‐
tional 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 end‐
point.
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 iden‐
tical). The relationship between these angles and angles expressed in
the normal coordinate system of the screen (as measured with a protrac‐
tor) 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 nor‐
mal_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 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 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
A value for a Drawable argument does not name a defined Window or
Pixmap. A value for a GContext argument does not name a defined GCon‐
text. An InputOnly window is used as a Drawable. 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 ALSOXDrawLine(3X11), XDrawPoint(3X11), XDrawRectangle(3X11)
Xlib -- C Language X Interface
XDrawArc(3X11)
