NAME XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGetFontProperty,
XUnloadFont, XCharStruct, XFontProp, XChar2b, XFontStruct - load or unload fonts and font metric structures SYNTAX Font XLoadFont(Display *display, char *name); XFontStruct *XQueryFont(Display *display, XID fontID); XFontStruct *XLoadQueryFont(Display *display, char *name); int XFreeFont(Display *display, XFontStruct *fontstruct); Bool XGetFontProperty(XFontStruct *fontstruct, Atom atom, unsigned long *valuereturn); int XUnloadFont(Display *display, Font font); ARGUMENTS atom Specifies the atom for the property name you want returned. display Specifies the connection to the X server. font Specifies the font. fontID Specifies the font ID or the GContext ID. fontstruct Specifies the storage associated with the font. gc Specifies the GC.
name Specifies the name of the font, which is a null-terminated string. valuereturn Returns the value of the font property. DESCRIPTION The XLoadFont function loads the specified font and returns its associ‐ ated font ID. If the font name is not in the Host Portable Character
Encoding, the result is implementation-dependent. Use of uppercase or lowercase does not matter. When the characters ``?'' and ``*'' are used in a font name, a pattern match is performed and any matching font is used. In the pattern, the ``?'' character will match any single character, and the ``*'' character will match any number of characters. A structured format for font names is specified in the X Consortium standard X Logical Font Description Conventions. If XLoadFont was unsuccessful at loading the specified font, a BadName error results. Fonts are not associated with a particular screen and can be stored as a component of any GC. When the font is no longer needed, call XUn‐ loadFont. XLoadFont can generate BadAlloc and BadName errors. The XQueryFont function returns a pointer to the XFontStruct structure, which contains information associated with the font. You can query a font or the font stored in a GC. The font ID stored in the XFontStruct structure will be the GContext ID, and you need to be careful when using this ID in other functions (see XGContextFromGC). If the font does not exist, XQueryFont returns NULL. To free this data, use XFree‐ FontInfo. XLoadQueryFont can generate a BadAlloc error. The XLoadQueryFont function provides the most common way for accessing a font. XLoadQueryFont both opens (loads) the specified font and returns a pointer to the appropriate XFontStruct structure. If the font name is not in the Host Portable Character Encoding, the result is
implementation-dependent. If the font does not exist, XLoadQueryFont returns NULL. The XFreeFont function deletes the association between the font resource ID and the specified font and frees the XFontStruct structure. The font itself will be freed when no other resource references it. The data and the font should not be referenced again. XFreeFont can generate a BadFont error. Given the atom for that property, the XGetFontProperty function returns the value of the specified font property. XGetFontProperty also returns False if the property was not defined or True if it was defined. A set of predefined atoms exists for font properties, which can be found in
. This set contains the standard proper‐ ties associated with a font. Although it is not guaranteed, it is likely that the predefined font properties will be present. The XUnloadFont function deletes the association between the font resource ID and the specified font. The font itself will be freed when no other resource references it. The font should not be referenced again. XUnloadFont can generate a BadFont error. STRUCTURES The XFontStruct structure contains all of the information for the font and consists of the font-specific information as well as a pointer to an array of XCharStruct structures for the characters contained in the font. The XFontStruct, XFontProp, and XCharStruct structures contain: typedef struct { short lbearing; /* origin to left edge of raster */ short rbearing; /* origin to right edge of raster */ short width; /* advance to next char's origin */ short ascent; /* baseline to top edge of raster */ short descent; /* baseline to bottom edge of raster */ unsigned short attributes; /* per char flags (not predefined) */ } XCharStruct; typedef struct { Atom name; unsigned long card32; } XFontProp; typedef struct { /* normal 16 bit characters are two bytes */ unsigned char byte1; unsigned char byte2; } XChar2b; typedef struct { XExtData *extdata; /* hook for extension to hang data */ Font fid; /* Font id for this font */ unsigned direction; /* hint about the direction font is painted */ unsigned mincharorbyte2; /* first character */ unsigned maxcharorbyte2; /* last character */ unsigned minbyte1; /* first row that exists */ unsigned maxbyte1; /* last row that exists */ Bool allcharsexist; /* flag if all characters have nonzero size */ unsigned defaultchar; /* char to print for undefined character */ int nproperties; /* how many properties there are */ XFontProp *properties; /* pointer to array of additional properties */ XCharStruct minbounds; /* minimum bounds over all existing char */ XCharStruct maxbounds; /* maximum bounds over all existing char */ XCharStruct *perchar; /* firstchar to lastchar information */ int ascent; /* logical extent above baseline for spacing */ int descent; /* logical decent below baseline for spacing */ } XFontStruct; X supports single byte/character, two bytes/character matrix, and
16-bit character text operations. Note that any of these forms can be used with a font, but a single byte/character text request can only
specify a single byte (that is, the first row of a 2-byte font). You
should view 2-byte fonts as a two-dimensional matrix of defined charac‐ ters: byte1 specifies the range of defined rows and byte2 defines the range of defined columns of the font. Single byte/character fonts have one row defined, and the byte2 range specified in the structure defines a range of characters. The bounding box of a character is defined by the XCharStruct of that character. When characters are absent from a font, the defaultchar is used. When fonts have all characters of the same size, only the infor‐ mation in the XFontStruct min and max bounds are used. The members of the XFontStruct have the following semantics: · The direction member can be either FontLeftToRight or FontRight‐ ToLeft. It is just a hint as to whether most XCharStruct elements have a positive (FontLeftToRight) or a negative (FontRightToLeft) character width metric. The core protocol defines no support for vertical text. · If the minbyte1 and maxbyte1 members are both zero, mincharorbyte2 specifies the linear character index correspond‐ ing to the first element of the perchar array, and maxcharorbyte2 specifies the linear character index of the last element. If either minbyte1 or maxbyte1 are nonzero, both mincharorbyte2 and maxcharorbyte2 are less than 256, and the
2-byte character index values corresponding to the perchar array element N (counting from 0) are: byte1 = N/D + minbyte1 byte2 = N\D + mincharorbyte2 where:
D = maxcharorbyte2 - mincharorbyte2 + 1 / = integer division \\ = integer modulus · If the perchar pointer is NULL, all glyphs between the first and last character indexes inclusive have the same information, as given by both minbounds and maxbounds. · If allcharsexist is True, all characters in the perchar array have nonzero bounding boxes. · The defaultchar member specifies the character that will be used when an undefined or nonexistent character is printed. The
defaultchar is a 16-bit character (not a 2-byte character). For
a font using 2-byte matrix format, the defaultchar has byte1 in
the most-significant byte and byte2 in the least significant byte. If the defaultchar itself specifies an undefined or nonexistent character, no printing is performed for an undefined or nonexis‐ tent character. · The minbounds and maxbounds members contain the most extreme values of each individual XCharStruct component over all elements of this array (and ignore nonexistent characters). The bounding box of the font (the smallest rectangle enclosing the shape obtained by superimposing all of the characters at the same origin
[x,y]) has its upper-left coordinate at:
[x + minbounds.lbearing, y - maxbounds.ascent] Its width is:
maxbounds.rbearing - minbounds.lbearing Its height is: maxbounds.ascent + maxbounds.descent · The ascent member is the logical extent of the font above the baseline that is used for determining line spacing. Specific characters may extend beyond this. · The descent member is the logical extent of the font at or below the baseline that is used for determining line spacing. Specific characters may extend beyond this.
· If the baseline is at Y-coordinate y, the logical extent of the
font is inclusive between the Y-coordinate values (y -
font.ascent) and (y + font.descent - 1). Typically, the minimum interline spacing between rows of text is given by ascent + descent. For a character origin at [x,y], the bounding box of a character (that is, the smallest rectangle that encloses the character's shape) described in terms of XCharStruct components is a rectangle with its
upper-left corner at:
[x + lbearing, y - ascent] Its width is:
rbearing - lbearing Its height is: ascent + descent The origin for the next character is defined to be: [x + width, y] The lbearing member defines the extent of the left edge of the charac‐ ter ink from the origin. The rbearing member defines the extent of the right edge of the character ink from the origin. The ascent member defines the extent of the top edge of the character ink from the ori‐ gin. The descent member defines the extent of the bottom edge of the character ink from the origin. The width member defines the logical width of the character. DIAGNOSTICS BadAlloc The server failed to allocate the requested resource or server memory. BadFont A value for a Font or GContext argument does not name a defined Font. BadName A font or color of the specified name does not exist. SEE ALSO XCreateGC(3), XListFonts(3), XSetFontPath(3)
Xlib - C Language X Interface X Version 11 libX11 1.6.5 XLoadFont(3)