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Table of Contents
XDrawArc, XDrawArcs,
XArc - draw arcs and arc structure
- 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);
- 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. and specify the upper-left corner of the bounding rectangle
- x
- y
- Specify the x and y coordinates, which are relative to the origin of
the drawable.
eqn not supported
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 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:
0
0>=40 .vs 0u
0<=39 .vs 0p
% 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
0>=40 .vs 0u
0<=39 .vs 0p
%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 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.
XDrawArc and XDrawArcs
can generate BadDrawable, BadGC, and BadMatch errors.
The
XArc structure contains:
0
0>=40 .vs 0u
0<=39 .vs 0p
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.
- 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.
XDrawLine(3X11)
, XDrawPoint(3X11)
, XDrawRectangle(3X11)
Xlib - C Language X Interface
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