XDrawArc(3X11) X11R5 XDrawArc(3X11)NAME
XDrawArc, XDrawArcs, XArc - draw arcs and arc structure
SYNTAX
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 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
draws a single circular or elliptical arc, and 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 rec‐
tangle, 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, or 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 infin‐
itely 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 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 normal-angle in the range [ pi/2, 3pi/2 ]
2pi for normal-angle in the range [ 3pi/2, 2pi ]
For any given arc, and 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, and 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 counter‐
clockwise 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.
and can generate and errors.
STRUCTURES
The 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 GContext.
An 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)