_X_L_o_a_d_F_o_n_t can generate _B_a_d_A_l_l_o_c and _B_a_d_N_a_m_e errors.
The _X_Q_u_e_r_y_F_o_n_t function returns a pointer to the _X_F_o_n_t_S_t_r_u_c_t 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 _X_F_o_n_t_S_t_r_u_c_t structure will be the _G_C_o_n_t_e_x_t ID, and you need to be careful when using this ID in other functions (see _X_G_C_o_n_t_e_x_t_F_r_o_m_G_C). If the font does not exist, _X_Q_u_e_r_y_F_o_n_t returns NULL. To free this data, use _X_F_r_e_e_F_o_n_t_I_n_f_o.
_X_L_o_a_d_Q_u_e_r_y_F_o_n_t can generate a _B_a_d_A_l_l_o_c error.
The _X_L_o_a_d_Q_u_e_r_y_F_o_n_t function provides the most common way for accessing a font. _X_L_o_a_d_Q_u_e_r_y_F_o_n_t both opens (loads) the specified font and returns a pointer to the appropriate _X_F_o_n_t_S_t_r_u_c_t structure. If the font name is not in the Host Portable Character Encoding, the result is implementation-dependent. If the font does not exist, _X_L_o_a_d_Q_u_e_r_y_F_o_n_t returns NULL.
The _X_F_r_e_e_F_o_n_t function deletes the association between the font resource ID and the specified font and frees the _X_F_o_n_t_S_t_r_u_c_t structure. The font itself will be freed when no other resource references it. The data and the font should not be referenced again.
_X_F_r_e_e_F_o_n_t can generate a _B_a_d_F_o_n_t error.
Given the atom for that property, the _X_G_e_t_F_o_n_t_P_r_o_p_e_r_t_y function returns the value of the specified font property. _X_G_e_t_F_o_n_t_P_r_o_p_e_r_t_y also returns _F_a_l_s_e if the property was not defined or _T_r_u_e if it was defined. A set of predefined atoms exists for font properties, which can be found in <_X_1_1_/_X_a_t_o_m_._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 _X_U_n_l_o_a_d_F_o_n_t 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.
_X_U_n_l_o_a_d_F_o_n_t can generate a _B_a_d_F_o_n_t error.
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 *ext_data; /* hook for extension to hang data */ Font fid; /* Font id for this font */ unsigned direction; /* hint about the direction 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 */ 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 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 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 _X_C_h_a_r_S_t_r_u_c_t of that character. When characters are absent from a font, the default_char is used. When fonts have all characters of the same size, only the information in the _X_F_o_n_t_S_t_r_u_c_t min and max bounds are used.
The members of the _X_F_o_n_t_S_t_r_u_c_t have the following semantics:
byte1 = N/D + min_byte1 byte2 = N\D + min_char_or_byte2
D = max_char_or_byte2 - min_char_or_byte2 + 1 / = integer division \\ = integer modulus
[x + min_bounds.lbearing, y - max_bounds.ascent]
max_bounds.rbearing - min_bounds.lbearing
max_bounds.ascent + max_bounds.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 _X_C_h_a_r_S_t_r_u_c_t 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 character 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 origin. 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.