Labels

A label is a typographical box. Since a L^ATEX box occupies a rectangle on the printed page, a single location is not enough information to position a label within a figure; an alignment point is needed in addition. By default, the alignment point of a text box is its reference point, the intersection of the left edge and the baseline, which is used by L^ATEX to position the box on the page: An alignment point may be shifted manually:

  label(P(3,2), P(2,-1), "$\\rho=\\sin \\theta$");

typesets the equation $\rho=\sin\theta$ and places the resulting text box at Cartesian location $(3,2)$, but shifted right by 2pt and down by 1pt. Note that C++ treats ``\\'' as a ``backslash control sequence'', so a double backslash is needed in the source to get a single backslash in the output. The general label commands are:

  label(P posn, P offset, <label text>);
  label(P posn, <label text>);
  label(P posn, P offset, <label text>, align);

The first command prints a label with its L^ATEX reference point at the Cartesian location posn, offset in true points (on the page) by the specified amount. Offsets of 2, 4, 6, 12, or 18 points work well with a 12-point font.

The second command prints the label text in a L^ATEX box centered at posn. While this is perhaps the most obvious way of placing a label, it may not be the correct method, since labels often mark a geometric object that should not be covered by the label.

In the third command, the align option may be one--or an appropriate pair--of t, b, r, or l (top, bottom, right, left), or c (center). As with offsets, these alignment options specify the position of the label relative to the Cartesian location $p$, namely they work opposite to the way they work in L^ATEX. For example, the alignment option br puts the label below and to the right of $p$.

Each label command has a corresponding ``mask'' version (masklabel) that draws an opaque white rectangle under the label text. Masking is useful when the text of a label sits in a cluttered part of the figure. An eepic file containing masklabels requires the pstcol package.

Labels can be rotated; the angle is set in current angle units with the command label_angle(theta). A rotation angle of 90 degrees prints labels suitable for a vertical axis. An eepic file containing rotated labels requires the rotating package.

When constructing and placing a label, keep in mind that

• Alignment offsets are specified in pt (i.e., page coordinates), not in Cartesian units, because the alignment point should not depend on the logical or printed size of the figure.

• The label text is enclosed in double quotes (the single character "), and contains the L^ATEX code to generate the label. Backslashes are doubled.