XDrawArc(3X11) XLIB FUNCTIONS 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 rela-
tive 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 rela-
tive 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 rectangle and two angles. The
center of the circle or ellipse is the center of the rect-
angle, and the major and minor axes are specified by the
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XDrawArc(3X11) XLIB FUNCTIONS XDrawArc(3X11)
width and height. Positive angles indicate counterclock-
wise 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 describ-
ing 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 trun-
cated 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 cir-
cle/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 cir-
cle/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 pro-
tractor) is as follows:
skewed-angle=atan(tan(normal-angle)*______)+adjust
The skewed-angle and normal-angle 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:
0 for normal-angle in the range [0,_]
n for normal-angle in the range [_,__]
2n for normal-angle 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 line-width is greater than zero and the arcs inter-
sect, 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 counter-
clockwise 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
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XDrawArc(3X11) XLIB FUNCTIONS XDrawArc(3X11)
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 hor-
izontal or vertical line can be drawn. Angles are com-
puted 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 compo-
nents: foreground, background, tile, stipple, tile-stip-
ple-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
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 cor-
rect 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
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