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 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
delim %% 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.
For an arc specified as %[ ~x, ~y, ~width , ~height, ~angle1, ~angle2 ]%,
the origin of the major and minor axes is at % [ x +^ {width over 2} , ~y
+^ {height over 2} ]%, and the infinitely thin path describing the entire
circle or ellipse intersects the horizontal axis at % [ x, ~y +^ {height
over 2} ]% and % [ x +^ width , ~y +^ { height over 2 }] % and intersects
the vertical axis at % [ x +^ { width over 2 } , ~y ]% and % [ x +^ { width
over 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 identi-
cal). The relationship between these angles and angles expressed in the
normal coordinate system of the screen (as measured with a protractor) is
as follows:
% roman "skewed-angle" ~ = ~ atan left ( tan ( roman "normal-angle" )
* width over height right ) +^ adjust%
The skewed-angle and normal-angle are expressed in radians (rather than in
degrees scaled by 64) in the range % [ 0 , ~2 pi ]% and where atan returns
a value in the range % [ - pi over 2 , ~pi over 2 ] % and adjust is:
%0% for normal-angle in the range % [ 0 , ~pi over 2 ]%
%pi% for normal-angle in the range % [ pi over 2 , ~{3 pi} over 2 ]%
%2 pi% for normal-angle in the range % [ {3 pi} over 2 , ~2 pi ]%
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 follow-
ing 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 sys-
tem 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 coordi-
nates 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