XDrawArc(3X11) X11 SDE 5.4R3.00 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
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 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.
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XDrawArc(3X11) X11 SDE 5.4R3.00 XDrawArc(3X11)
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 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:
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, 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.
Licensed material--property of copyright holder(s) 2
XDrawArc(3X11) X11 SDE 5.4R3.00 XDrawArc(3X11)
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.
SEE ALSO
XDrawLine(3X11), XDrawPoint(3X11), XDrawRectangle(3X11)
Xlib - C Language X Interface
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