Tk_FontId(3)

NAME
Tk_FontId, Tk_GetFontMetrics, Tk_PostscriptFontName - accessor functions for fonts

SYNOPSIS
#include <tk.h>

Font
Tk_FontId(tkfont)

void
Tk_GetFontMetrics(tkfont, fmPtr)

int
Tk_PostscriptFontName(tkfont, dsPtr)

ARGUMENTS
Opaque font token being queried. Must have been returned by a previous call to Tk_GetFont. Pointer to structure in which the font metrics for tkfont will be stored. Pointer to an initialized Tcl_DString to which the name of the Postscript font that corresponds to tkfont will be appended.

DESCRIPTION

Given a tkfont, Tk_FontId returns the token that should be selected into an XGCValues structure in order to construct a graphics context that can be used to draw text in the specified font.

Tk_GetFontMetrics computes the ascent, descent, and linespace of the tkfont in pixels and stores those values in the structure pointer to by fmPtr. These values can be used in computations such as to space multiple lines of text, to align the baselines of text in different fonts, and to vertically align text in a given region. See the documentation for the font command for definitions of the terms ascent, descent, and linespace, used in font metrics.

Tk_PostscriptFontName maps a tkfont to the corresponding Postcript font name that should be used when printing. The return value is the size in points of the tkfont and the Postscript font name is appended to dsPtr. DsPtr must refer to an initialized Tcl_DString. Given a ``reasonable'' Postscript printer, the following screen font families should print correctly:

    Avant Garde, Arial, Bookman, Courier, Courier New, Geneva, Helvetica, Monaco, New Century Schoolbook, New York, Palatino, Symbol, Times, Times New Roman, Zapf Chancery, and Zapf Dingbats.

Any other font families may not print correctly because the computed Postscript font name may be incorrect or not exist on the printer.

DATA STRUCTURES
The Tk_FontMetrics data structure is used by Tk_GetFontMetrics to return information about a font and is defined as follows:
    typedef struct Tk_FontMetrics {
        int ascent;
        int descent;
        int linespace;
    } Tk_FontMetrics;
The linespace field is the amount in pixels that the tallest letter sticks up above the baseline, plus any extra blank space added by the designer of the font.

The descent is the largest amount in pixels that any letter sticks below the baseline, plus any extra blank space added by the designer of the font.

The linespace is the sum of the ascent and descent. How far apart two lines of text in the same font should be placed so that none of the characters in one line overlap any of the characters in the other line.

KEYWORDS
font