XDrawArc(3X11) RISC/os Reference Manual 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 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 rela-
tive 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. Each
arc is specified by a rectangle and two angles. The center
of the circle or ellipse is the center of the rectangle, and
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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 magni-
tude 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], h
te
he
igh
or
t]
i,
gia
nnd
ofth
te
he
width, y+
major and minor axes is at [x+ 2
infinitely thin path describing 2
the entire circle or ellipse
height] and
intersects the horizontal axis at [x, y+
height] and intersects the ver2
tical axis at
[x+width, y+ width, y+height]. These coordinates can
width, y] an2
d [x+
[x+ 2
be fr2
actional and so are not truncated to discrete coordi-
nates. The path should be defined by the ideal mathematical
path. For a wide line with line-width lw, the bounding out-
lines 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 rangπ
e][0
a,
nd2π]
π,
and where atan returns a value in the range [- 2
adjust is: 2
π]
0 for normal-angle in the range [0, 3π]
π, 2
π for normal-angle in the range [ 3π,22π]
2π for normal-angle in the range [2
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
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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 com-
ponents: 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
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.
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XDrawArc(3X11) RISC/os Reference Manual XDrawArc(3X11)
SEE ALSO
Xlib - C Language X Interface
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