XDrawArc(3) XLIB FUNCTIONS XDrawArc(3)
NAME
XDrawArc, XDrawArcs, XArc - draw arcs and arc structure
SYNTAX
int XDrawArc(Display *display, Drawable d, GC gc, int x, int y, unsigned int width, unsigned int height, int angle1, int angle2);
int XDrawArcs(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 bound-
ing 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 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], the origin of the major and minor axes is at [x+_____,y+______], and the infin-
itely thin path describing the entire circle or ellipse intersects the horizontal axis at [x,y+______] and [x+width,y+______] and inter-
sects the vertical axis at [x+_____,y] and [x+_____,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 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 corre-
sponding 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)*______)+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:
l l. 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 intersect, XDrawArc and XDrawArcs do not draw a pixel more than once. Otherwise, the intersecting pixels of inter-
secting 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 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.
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(3), XDrawPoint(3), XDrawRectangle(3)
Xlib - C Language X Interface
X Version 11 libX11 1.5.0 XDrawArc(3)