1XDrawArc(3)                     XLIB FUNCTIONS                     XDrawArc(3)
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4

NAME

6       XDrawArc, XDrawArcs, XArc - draw arcs and arc structure
7

SYNTAX

9       int XDrawArc(Display *display, Drawable d, GC gc, int x, int y,
10              unsigned int width, unsigned int height, int angle1, int
11              angle2);
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13       int XDrawArcs(Display *display, Drawable d, GC gc, XArc *arcs, int
14              narcs);
15

ARGUMENTS

17       angle1    Specifies the start of the arc relative to the three-o'clock
18                 position from the center, in units of degrees * 64.
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20       angle2    Specifies the path and extent of the arc relative to the
21                 start of the arc, in units of degrees * 64.
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23       arcs      Specifies an array of arcs.
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25       d         Specifies the drawable.
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27       display   Specifies the connection to the X server.
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29       gc        Specifies the GC.
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31       narcs     Specifies the number of arcs in the array.
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33       width
34       height    Specify the width and height, which are the major and minor
35                 axes of the arc.
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37       x
38       y         Specify the x and y coordinates, which are relative to the
39                 origin of the drawable and specify the upper-left corner of
40                 the bounding rectangle.
41

DESCRIPTION

43       XDrawArc draws a single circular or elliptical arc, and XDrawArcs draws
44       multiple circular or elliptical arcs.  Each arc is specified by a rec‐
45       tangle and two angles.  The center of the circle or ellipse is the cen‐
46       ter of the rectangle, and the major and minor axes are specified by the
47       width and height.  Positive angles indicate counterclockwise motion,
48       and negative angles indicate clockwise motion.  If the magnitude of
49       angle2 is greater than 360 degrees, XDrawArc or XDrawArcs truncates it
50       to 360 degrees.
51
52       For an arc specified as [x,y,width,height,angle1,angle2], the origin of
53       the major and minor axes is at [x+w_i_d2_t_h_,y+h_e_i_g2_h_t_], and the infinitely
54       thin path describing the entire circle or ellipse intersects the hori‐
55       zontal axis at [x,y+h_e_i_g2_h_t_] and [x+width,y+h_e_i_g2_h_t_] and intersects the
56       vertical axis at [x+w_i_d2_t_h_,y] and [x+w_i_d2_t_h_,y+height].  These coordinates
57       can be fractional and so are not truncated to discrete coordinates.
58       The path should be defined by the ideal mathematical path.  For a wide
59       line with line-width lw, the bounding outlines for filling are given by
60       the two infinitely thin paths consisting of all points whose perpendic‐
61       ular distance from the path of the circle/ellipse is equal to lw/2
62       (which may be a fractional value).  The cap-style and join-style are
63       applied the same as for a line corresponding to the tangent of the cir‐
64       cle/ellipse at the endpoint.
65
66       For an arc specified as [x,y,width,height,angle1,angle2], the angles
67       must be specified in the effectively skewed coordinate system of the
68       ellipse (for a circle, the angles and coordinate systems are identi‐
69       cal).  The relationship between these angles and angles expressed in
70       the normal coordinate system of the screen (as measured with a protrac‐
71       tor) is as follows:
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73       skewed-angle=atan⎛⎝tan(normal-angle)*h_we_ii_dg_th_ht_⎞⎠+adjust
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75       The skewed-angle and normal-angle are expressed in radians (rather than
76       in degrees scaled by 64) in the range [0,2π] and where atan returns a
77       value in the range [−π2_,π2_] and adjust is:
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79       l l.  0    for normal-angle in the range [0,π2_] π    for normal-angle in
80       the range [π2_,3_π2_] 2π   for normal-angle in the range [3_π2_,2π]
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82       For any given arc, XDrawArc and XDrawArcs do not draw a pixel more than
83       once.  If two arcs join correctly and if the line-width is greater than
84       zero and the arcs intersect, XDrawArc and XDrawArcs do not draw a pixel
85       more than once.  Otherwise, the intersecting pixels of intersecting
86       arcs are drawn multiple times.  Specifying an arc with one endpoint and
87       a clockwise extent draws the same pixels as specifying the other end‐
88       point and an equivalent counterclockwise extent, except as it affects
89       joins.
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91       If the last point in one arc coincides with the first point in the fol‐
92       lowing arc, the two arcs will join correctly.  If the first point in
93       the first arc coincides with the last point in the last arc, the two
94       arcs will join correctly.  By specifying one axis to be zero, a hori‐
95       zontal or vertical line can be drawn.  Angles are computed based solely
96       on the coordinate system and ignore the aspect ratio.
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98       Both functions use these GC components: function, plane-mask, line-
99       width, line-style, cap-style, join-style, fill-style, subwindow-mode,
100       clip-x-origin, clip-y-origin, and clip-mask.  They also use these GC
101       mode-dependent components: foreground, background, tile, stipple, tile-
102       stipple-x-origin, tile-stipple-y-origin, dash-offset, and dash-list.
103
104       XDrawArc and XDrawArcs can generate BadDrawable, BadGC, and BadMatch
105       errors.
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STRUCTURES

108       The XArc structure contains:
109
110       typedef struct {
111            short x, y;
112            unsigned short width, height;
113            short angle1, angle2;             /* Degrees * 64 */
114       } XArc;
115
116       All x and y members are signed integers.  The width and height members
117       are 16-bit unsigned integers.  You should be careful not to generate
118       coordinates and sizes out of the 16-bit ranges, because the protocol
119       only has 16-bit fields for these values.
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DIAGNOSTICS

122       BadDrawable
123                 A value for a Drawable argument does not name a defined Win‐
124                 dow or Pixmap.
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126       BadGC     A value for a GContext argument does not name a defined GCon‐
127                 text.
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129       BadMatch  An InputOnly window is used as a Drawable.
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131       BadMatch  Some argument or pair of arguments has the correct type and
132                 range but fails to match in some other way required by the
133                 request.
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SEE ALSO

136       XDrawLine(3), XDrawPoint(3), XDrawRectangle(3)
137       Xlib - C Language X Interface
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141X Version 11                     libX11 1.6.4                      XDrawArc(3)
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