XDrawArc, XDrawArcs, XArc - draw arcs and arc structure

Syntax

Arguments

Description

Structures

Diagnostics

int XDrawArc(Display * display, Drawabled, GCgc, intx, inty, unsigned intwidth, unsigned intheight, intangle1, intangle2);

int XDrawArcs(Display *display, Drawabled, GCgc, XArc *arcs, intnarcs);

angle1Specifies the start of the arc relative to the three-o’clock position from the center, in units of degrees * 64. angle2Specifies the path and extent of the arc relative to the start of the arc, in units of degrees * 64. arcsSpecifies an array of arcs. dSpecifies the drawable. displaySpecifies the connection to the X server. gcSpecifies the GC. narcsSpecifies the number of arcs in the array. widthheightSpecify the width and height, which are the major and minor axes of the arc. and specify the upper-left corner of the bounding rectangle xySpecify the x and y coordinates, which are relative to the origin of the drawable.

XDrawArcdraws a single circular or elliptical arc, andXDrawArcsdraws 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,XDrawArcorXDrawArcstruncates 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/ 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:

roman "skewed-angle" ~ = ~ atan left ( tan ( roman "normal-angle" ) 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]pifor normal-angle in the range [ pi/ 2, 3pi/ 2]2 pifor normal-angle in the range [3 pi/ 2, 2pi]For any given arc,

XDrawArcandXDrawArcsdo 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,XDrawArcandXDrawArcsdo 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.

XDrawArcandXDrawArcscan generateBadDrawable,BadGC, andBadMatcherrors.

TheXArcstructure 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 coordinates and sizes out of the 16-bit ranges, because the protocol only has 16-bit fields for these values.

BadDrawableA value for a Drawable argument does not name a defined Window or Pixmap. BadGCA value for a GContext argument does not name a defined GContext. BadMatchAn InputOnlywindow is used as a Drawable.BadMatchSome argument or pair of arguments has the correct type and range but fails to match in some other way required by the request.

XDrawLine(3), XDrawPoint(3), XDrawRectangle(3)

Xlib - C Language X Interface

X Version 11 |
XDrawArc (3) | libX11 1.5.0 |