2.4.2 Path elements

The class pathitem is the superclass of all PostScript path construction primitives. It is never used directly, but only by instantiating its subclasses, which correspond one by one to the PostScript primitives.

Except for the path elements ending in _pt, all coordinates passed to the path elements can be given as number (in which case they are interpreted as user units with the currently set default type) or in PyX lengths.

The following operation move the current point and open a new subpath:

class moveto( x, y): Path element which sets the current point to the absolute coordinates (x, y). This operation opens a new subpath.

class rmoveto( dx, dy): Path element which moves the current point by (dx, dy). This operation opens a new subpath.

Drawing a straight line can be accomplished using:

class lineto( x, y): Path element which appends a straight line from the current point to the point with absolute coordinates (x, y), which becomes the new current point.

class rlineto( dx, dy): Path element which appends a straight line from the current point to the a point with relative coordinates (dx, dy), which becomes the new current point.

For the construction of arc segments, the following three operations are available:

class arc( x, y, r, angle1, angle2): Path element which appends an arc segment in counterclockwise direction with absolute coordinates (x, y) of the center and radius r from angle1 to angle2 (in degrees). If before the operation, the current point is defined, a straight line is from the current point to the beginning of the arc segment is prepended. Otherwise, a subpath, which thus is the first one in the path, is opened. After the operation, the current point is at the end of the arc segment.

class arcn( x, y, r, angle1, angle2): Path element which appends an arc segment in clockwise direction with absolute coordinates (x, y) of the center and radius r from angle1 to angle2 (in degrees). If before the operation, the current point is defined, a straight line is from the current point to the beginning of the arc segment is prepended. Otherwise, a subpath, which thus is the first one in the path, is opened. After the operation, the current point is at the end of the arc segment.

class arct( x1, y1, x2, y2, r): Path element which appends an arc segment of radius r connecting between (x1, y1) and (x2, y2).

Bézier curves can be constructed using:

class curveto( x1, y1, x2, y2, x3, y3): Path element which appends a Bézier curve with the current point as first control point and the other control points (x1, y1), (x2, y2), and (x3, y3).

class rcurveto( dx1, dy1, dx2, dy2, dx3, dy3): Path element which appends a Bézier curve with the current point as first control point and the other control points defined relative to the current point by the coordinates (dx1, dy1), (dx2, dy2), and (dx3, dy3).

Note that when calculating the bounding box (see Sect. 10) of Bézier curves, PyX uses for performance reasons the so-called control box, i.e., the smallest rectangle enclosing the four control points of the Bézier curve. In general, this is not the smallest rectangle enclosing the Bézier curve.

Finally, an open subpath can be closed using:

class closepath( ): Path element which closes the current subpath.

For performance reasons, two non-PostScript path elements are defined, which perform multiple identical operations:

class multilineto_pt( points_pt): Path element which appends straight line segments starting from the current point and going through the list of points given in the points_pt argument. All coordinates have to be given in PostScript points.

class multicurveto_pt( points_pt): Path element which appends Bézier curve segments starting from the current point and going through the list of each three control points given in the points_pt argument.