XLoadFont(3X) XLoadFont(3X)NAME XLoadFont, XQueryFont, XLoadQueryFont, XFreeFont, XGetFontProperty, XUnloadFont - manipulate fonts and the XFontStruct structure SYNOPSIS Font XLoadFont (display, name) Display *display; char *name; XFontStruct *XQueryFont (display, font-ID) Display *display; XID font-ID; XFontStruct *XLoadQueryFont (display, name) Display *display; char *name; XFreeFont (display, font-struct) Display *display; XFontStruct *font-struct; Bool XGetFontProperty (font-struct, atom, value-return) XFontStruct *font-struct; Atom atom; unsigned long *value-return; XUnloadFont (display, font) Display *display; Font font; DESCRIPTION The XLoadFont function loads the specified font and returns its associated font ID. The name argument should be ISO Latin-1 encoding; case does not matter. The interpretation of the question mark (?) and the asterisk (*) in name is not defined by the core protocol but is reserved for future definition. A structured format for font names is specified in the X Consortium standard X Logical Font Description Conventions. If XLoadFont is un- successful 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 graphic context. When the font is no longer needed, call XUnloadFont. 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 graphic context. The font ID stored in the XFontStruct structure is the GContext ID, and you need to be careful when using this ID in other functions (see XGContextFromGC). To free this November, 1990 1
XLoadFont(3X) XLoadFont(3X)data, use XFreeFontInfo. 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 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 is freed when no other resource references it. The data and the font should not be referenced again. Given the atom for that property, the XGetFontProperty func- tion 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 <X11/Xatom.h>. This set contains the standard properties 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 is freed when no other resource references it. The font should not be referenced again. Arguments These functions accept the following arguments: atom Specifies the atom associated with the string name you want returned. display Specifies the connection to the X server. font Specifies the font. font-ID Specifies the ID of the font or the graphic context ID. font-struct Specifies the storage associated with the font. name Specifies the name of the font as a null-terminated string. value-return Returns the value of the font property. 2 November, 1990
XLoadFont(3X) XLoadFont(3X)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 are defined as fol- lows. 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 char- */ /* acters are two bytes */ unsigned char byte1; unsigned char byte2; } XChar2b; typedef struct { XExtData *ext_data;/* hook for extension */ /* to hang data */ Font fid; /* Font id for this font */ unsigned direction;/* hint about the direc- */ /* ion font is painted */ unsigned min_char_or_byte2;/* first character */ unsigned max_char_or_byte2;/* last character */ unsigned min_byte1;/* first row that exists */ unsigned max_byte1;/* last row that exists */ Bool all_chars_exist;/* flag if all characters */ /* have nonzero size */ unsigned default_char;/* char to print for */ /* undefined character */ int n_properties;/* how many properties */ /* there are */ XFontProp *properties;/* pointer to array of */ /* additional properties */ November, 1990 3
XLoadFont(3X) XLoadFont(3X)XCharStruct min_bounds;/* minimum bounds over */ /* all existing char */ XCharStruct max_bounds;/* maximum bounds over */ /* all existing char */ XCharStruct *per_char;/* first_char to */ /* last_char information */ int ascent; /* logical extent above */ /* baseline for spacing */ int descent; /* logical decent below */ /* baseline for spacing */ } XFontStruct; X supports a single byte per character, two-bytes-per- 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 characters: 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 XChar- Struct of that character. When characters are absent from a font, the default_char is used. When fonts have all charac- ters of the same size, only the information in the min_bounds and max_bounds members of the XFontStruct are used. The members of the XFontStruct have the following semantics: The direction member can be either FontLeftToRight or FontRightToLeft. 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 min_byte1 and max_byte1 members are both 0, min_char_or_byte2 specifies the linear character index corresponding to the first element of the per_char ar- ray, and max_char_or_byte2 specifies the linear charac- ter index of the last element. If either min_byte1 or max_byte1 are nonzero, both min_char_or_byte2 and max_char_or_byte2 are less than 256, and the 2-byte character index values correspond- ing to the per_char array element N (counting from 0) are: 4 November, 1990
XLoadFont(3X) XLoadFont(3X)byte1 = N/D + min_byte1 byte2 = N\D + min_char_or_byte2 where: D = max_char_or_byte2 - min_char_or_byte2 + 1 / = integer division \ = integer modulus If the per_char pointer is NULL, all glyphs between the first and last character indexes inclusive have the same information, as given by both min_bounds and max_bounds. If all_chars_exist is TRUE, all characters in the per_char array have nonzero bounding boxes. The default_char member specifies the character that will be used when an undefined or nonexistent character is printed. The default_char is a 16-bit character (not a 2-byte character). For a font using 2-byte matrix format, the default_char has byte1 in the most- significant byte and byte2 in the least-significant byte. If the default_char itself specifies an unde- fined or nonexistent character, no printing is per- formed for an undefined or nonexistent character. The min_bounds and max_bounds 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 smal- lest rectangle enclosing the shape obtained by superim- posing all of the characters at the same origin [x,y]) has its upper-left coordinate at: [x + min_bounds.lbearing, y - max_bounds.ascent] Its width is: max_bounds.rbearing - min_bounds.lbearing Its height is: max_bounds.ascent + max_bounds.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 November, 1990 5
XLoadFont(3X) XLoadFont(3X)spacing. Specific characters may extend beyond this. If the baseline is at Y-coordinate y, the logical ex- tent of the font is inclusive between the Y-coordinate values (y - font.ascent) and (y + font.descent - 1). Typical- ly, 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 char- acter (that is, the smallest rectangle that encloses the character's shape) described in terms of XCharStruct com- ponents 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 character ink from the origin. The rbearing member de- fines 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 origin. The descent member defines the extent of the bottom edge of the charac- ter ink from the origin. The width member defines the logi- cal width of the character. ERRORS BadAlloc The server failed to allocate the requested resource or server memory. BadFont A value for a Font or GC argument does not name a defined font. BadName A font or color of the specified name does not ex- ist. The XLoadFont function can generate BadAlloc and BadName errors. 6 November, 1990
XLoadFont(3X) XLoadFont(3X)The XLoadQueryFont function can generate a BadAlloc error. The XFreeFont and XUnloadFont functions can generate a Bad- Font error. SEE ALSO XListFonts(3X), XSetFontPath(3X)Xlib - C Language InterfaceNovember, 1990 7