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;
display | Specifies the connection to the X server. |
d | Specifies the drawable. |
gc | Specifies the GC. |
x | .ns |
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. |
width height | Specify the width and height, which are the major and minor axes of the arc. |
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. |
For an arc specified as [ x, y, width, height, angle1, angle2 ], the origin of the major and minor axes is at [ x + width / 2 , y + height / 2 ], and the infinitely thin path describing the entire circle or ellipse intersects the horizontal axis at [ x, y + height / 2 ] and [ x + width , y + height / 2 ] and intersects the vertical axis at [ x + width / 2, y ] and [ x + width / 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:
skewed-angle = atan ( tan ( normal-angle ) * width / height ) + 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 / 2 , pi / 2 ] and adjust is:
0 | for normal-angle in the range [ 0, pi / 2 ] |
pi | for normal-angle in the range [ pi / 2 , 3 pi / 2 ] |
2 pi | for normal-angle in the range [ 3 pi / 2 , 2 pi ] |
For any given arc, XDrawArc() does 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() does 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.
This function uses 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. It also uses these GC mode-dependent components: foreground, background, tile, stipple, tile-stipple-x-origin, tile-stipple-y-origin, dash-offset, and dash-list.
XDrawArc() can generate BadDrawable , BadGC , and BadMatch errors.
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. |