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XDrawArc
Section: XLIB FUNCTIONS (3) Updated: libX11 1.6.3 Index
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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 threeo'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 upperleft 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 linewidth 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 capstyle and joinstyle 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:
% roman "skewedangle" ~ = ~ atan left ( tan ( roman "normalangle" )
* width over height right ) +^ adjust%
The skewedangle and normalangle 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 normalangle in the range % [ 0 , ~pi over 2 ]%

%pi%  for normalangle in the range % [ pi over 2 , ~{3 pi} over 2 ]%

%2 pi%  for normalangle 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 linewidth 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, planemask, linewidth, linestyle, capstyle, joinstyle,
fillstyle, subwindowmode, clipxorigin, clipyorigin, and clipmask.
They also use these GC modedependent components:
foreground, background, tile, stipple, tilestipplexorigin,
tilestippleyorigin, dashoffset, and dashlist.
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 16bit unsigned integers.
You should be careful not to generate coordinates and sizes
out of the 16bit ranges, because the protocol only has 16bit 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
Index
 NAME

 SYNTAX

 ARGUMENTS

 DESCRIPTION

 STRUCTURES

 DIAGNOSTICS

 SEE ALSO

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