System Information

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Font-File Format


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This topic describes the file formats for


raster and vector fonts used by the Windows


Help with essay on System Information

operating system. These file formats may be


used by smart text generators in some support


modules for the graphics device interface


(GDI). Vector formats, however, are more


frequently used by GDI than by the support


modules.


Organization of a Font File


Raster and vector font files begin with


information that is common to both types of


file and then continue with information that


differs for each type. These font files are


stored with an .FNT extension.


In Windows versions .0 and later, the


font-file header for raster and vector fonts


includes six new members dFlags, dfAspace,


dfBspace, dfCspace, dfColorPointer, and


dfReserved1. All device drivers support the


fonts in Windows .x. However, not all drivers


support those in versions .0 and later.


In Windows, font files for raster and vector


fonts include the glyph table in the


dfCharTable member, which consists of


structures describing the bits for characters


in the font file.The use of -bit offsets to


the character glyphs in the dfCharTable member


enables fonts to exceed 64K, the size limit of


Windows .x fonts.


Because of their -bit offsets and


potentially large size, the newer fonts are


designed for use on systems that are running


Windows versions .0 and later in protected


(standard or 86-enhanced) mode and are using


an 8086 (or higher) processor whose -bit


registers can access the character glyphs.


Typically, newer drivers use the newer version


of a font only when both of these conditions


are true.


Font-File Structure


Font information is found at the beginning of


both raster and vector font files.


Following are the members of the TFONTINFO


structure


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dfVersion ³ The version (0x000 or 0x000) of the file.


dfSize ³ The total size of the file, in bytes.


dfCopyright ³ Copyright information.


dfType ³ The type of font file. This information is organized


³ as follows


Byte ³ Description


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Low-order ³ Exclusively for GDI use. If the low-order


³ bit of the word is zero, it is a bitmap


³ (raster) font file. If the low-order bit


³ is 1, it is a vector font file. The


³ second bit is reserved and must be zero.


³ If no bits follow in the file and the


³ bits are located in memory at a fixed


³ address specified by the dfBitsOffset


³ member, the third bit is set to 1.


³ Otherwise, the bit is set to zero. If the


³ font is realized by a device, the


³ high-order bit of the low-order byte is


³ set. The remaining bits in the low-order


³ byte are then reserved and set to zero.


High-order ³ Reserved for device use and is always


³ set to zero for standard fonts realized


³ by GDI. Physical fonts that set the


³ high-order bit of the low-order byte may


³ use this byte to describe themselves. GDI


³ never inspects the high-order byte.


dfPoints ³ The nominal point size (that is, the number


³ identifying the point size) at which this character


³ set looks best.


dfVertRes ³ The nominal vertical resolution (that is, the number


³ identifying the vertical resolution), in dots per


³ inch, at which this character set was digitized.


dfHorizRes ³ The nominal horizontal resolution (that is, the number


³ identifying the horizontal resolution), in dots per


³ inch, at which this character set was digitized.


dfAscent ³ The distance from the top of a character-definition


³ cell to the base line of the typographical font. The


³ dfAscent member is useful for aligning the base lines


³ of fonts with different heights.


dfInternalLeading ³ The amount of leading inside the bounds set by the


³ dfPixHeight member. Accent marks can occur in this


³ area. The designer can set the value to zero.


dfExternalLeading ³ The amount of extra leading that the designer requests


³ the application to add between rows. Since this area


³ is outside the font proper, it contains no marks and


³ is not altered by text-output calls in either opaque


³ or transparent mode. The designer can set the value to


³ zero.


dfItalic ³ Whether the character-definition data represents an


³ italic font. If the flag is set, the low-order bit is


³ 1. All other bits are zero.


dfUnderline ³ Whether the character-definition data represents an


³ underlined font. If the flag is set, the low-order bit


³ is 1. All other bits are zero.


dfStrikeOut ³ Whether the character-definition data represents a


³ strikeout font. If the flag is set, the low-order bit


³ is 1. All other bits are zero.


fWeight ³ Specifies the weight of the characters in the


³ character-definition data, on a scale of 1 through


³ 1000. A dfWeight value of 400 specifies a regular


³ weight.


dfCharSet ³ The character set defined by this font.


dfPixWidth ³ The width of the grid on which a vector font was


³ digitized. For raster fonts, if the dfPixWidth member


³ is nonzero, it represents the width for all the


³ characters in the bitmap. If the member is zero, the


³ font has variable-width characters whose widths are


³ specified in the array for the dfCharTable member.


dfPixHeight ³ The height of the character bitmap for raster fonts or


³ the height of the grid on which a vector font was


³ digitized.


dfPitchAndFamily ³ The pitch and font family. If the font is variable


³ pitch, the low bit is set. The four high bits give


³ the family name of the font. Font families describe


³ the general look of a font. They identify fonts when


³ the exact name is not available. The font families are


³ described as follows


Family ³ Description


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FF_DONTCARE ³ Unknown.


FF_ROMAN ³ Proportionally spaced fonts with


³ serifs.


FF_SWISS ³ Proportionally spaced fonts without


³ serifs.


FF_MODERN ³ Fixed-pitch fonts.


FF_SCRIPT ³ Cursive or script fonts. (Both are


³ designed to look similar to


³ handwriting. Script fonts have joined


³ letters; cursive fonts do not.)


FF_DECORATIVE ³ Novelty fonts.


dfAvgWidth ³ The width of characters in the font. For fixed-pitch


³ fonts, this value is the same as the value for the


³ dfPixWidth member. For variable-pitch fonts, it is the


³ width of the character X.


dfMaxWidth ³ The maximum pixel width of any character in the font.


³ For fixed-pitch fonts, this value is the same as the


³ value of the dfPixWidth member.


dfFirstChar ³ The first character code defined by the font.


³ Character definitions are stored only for the


³ characters actually present in the font. Use this


³ member, therefore, when calculating indexes for either


³ the dfBits or dfCharOffset member.


dfLastChar ³ The last character code defined by the font. All


³ characters with codes between the values for the


³ dfFirstChar and dfLastChar members must be present in


³ the character definitions for the font.


dfDefaultChar ³ The character to substitute whenever a string contains


³ a character that is out of range. The character is


³ given relative to the dfFirstChar member so that the


³ dfDefaultChar member is the actual value of the


³ character less the value of the dfFirstChar member.


³ The dfDefaultChar member indicates a special character


³ that is not a space.


dfBreakChar ³ The character that defines word breaks for word


³ wrapping and word-spacing justification. The character


³ is given relative to the dfFirstChar member so that


³ the dfBreakChar member is the actual value of the


³ character less that of the dfFirstChar member. The


³ dfBreakChar member is normally minus the value of


³ the dfFirstChar member (the ASCII space character).


dfWidthBytes ³ The number of bytes in each row of the bitmap. This


³ value is always even so that the rows start on word


³ boundaries. For vector fonts, this member has no


³ meaning.


dfDevice ³ The offset in the file to the string giving the device


³ name. For a generic font, this value is zero.


dfFace ³ The offset in the file to the null-terminated string


³ that names the face.


dfBitsPointer ³ The absolute machine address of the bitmap. This is


³ set by GDI at load time. The value of the


³ dfBitsPointer member is guaranteed to be even.


dfBitsOffset ³ The offset in the file to the beginning of the bitmap


³ information. If the third bit in the dfType member is


³ set, the dfBitsOffset member is an absolute address of


³ the bitmap (probably in read-only memory).


³ For raster fonts, the dfBitsOffset member points to a


³ sequence of bytes that make up the bitmap of the font.


³ The height of the bitmap is the height of the font,


³ and its width is the sum of the widths of the


³ characters in the font, rounded up to the next word


³ boundary.


³ For vector fonts, the dfBitsOffset member points to a


³ string of bytes or words (depending on the size of the


³ grid on which the font was digitized) that specify the


³ strokes for each character of the font. The value of


³ the dfBitsOffset member must be even.


dfReserved ³ Not used.


dfFlags ³ The bit flags that define the format of the glyph


³ bitmap, as follows


Pitch value ³ Address


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DFF_FIXED ³ 0x0001


DFF_PROPORTIONAL ³ 0x000


DFF_ABCFIXED ³ 0x0004


DFF_ABCPROPORTIONAL ³ 0x0008


DFF_1COLOR ³ 0x0010


DFF_16COLOR ³ 0x000


DFF_56COLOR ³ 0x0040


DFF_RGBCOLOR ³ 0x0080


dfAspace ³ The global A space, if any. The value of the dfAspace


³ member is the distance from the current position to


³ the left edge of the bitmap.


dfBspace ³ The global B space, if any. The value of the dfBspace


³ member is the width of the character.


dfCspace ³ The global C space, if any. The value of the dfCspace


³ member is the distance from the right edge of the


³ bitmap to the new current position. The increment of a


³ character is the sum of the A, B, and C spaces. These


³ spaces apply to all glyphs, including DFF_ABCFIXED.


dfColorPointer ³ The offset to the color table for color fonts, if any.


³ The format of the bits is like a device-independent


³ bitmap (DIB), but without the header. (That is, the


³ characters are not split into disjoint bytes; instead,


³ they are left intact.) If no color table is needed,


³ this entry is NULL.


dfReserved1 ³ Not used.


dfCharTable ³ An array of entries for raster, fixed-pitch vector,


³ and proportionally spaced vector fonts, as follows


Font type ³ Description


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Raster ³ Each entry in the array


³ consists of two -byte


³ words for Windows .x


³ and three -byte words


³ for Windows .0 and


³ later. The first word


³ of each entry is the


³ character width. The


³ second word of each


³ entry is the byte


³ offset from the


³ beginning of the


³ TFONTINFO structure to


³ the character bitmap.


³ For Windows .0 and


³ later, the second and


³ third words are used


³ for the offset.


Fixed-pitch vector ³ Each -byte entry in


³ the array specifies the


³ offset from the start


³ of the bitmap to the


³ beginning of the string


³ of stroke specification


³ units for the


³ character. The number


³ of bytes or words to be


³ used for a particular


³ character is calculated


³ by subtracting its


³ entry from the next


³ one, so that there is a


³ sentinel at the end


³ of the array of values.


Proportionally-spaced vector ³ Each 4-byte entry in


³ the array is divided


³ into two -byte fields.


³ The first field gives


³ the starting offset


³ from the start of the


³ bitmap of the character


³ strokes. The second


³ field gives the pixel


³ width of the character.


³ One extra entry at the


³ end of the character


³ table describes an


³ absolute-space


³ character, which is


³ guaranteed to be blank.


³ This character is not


³ part of the normal


³ character set.


³ The number of entries


³ in the table is


³ calculated as follows


³ (dfLastChar -


³ dfFirstChar) + . This


³ number includes a


³ spare, the sentinel


³ offset.


facename ³ An ASCII character string that constitutes the name of


³ the font face. The size of this member is the length


³ of the string plus a null terminating character.


devicename ³ An ASCII character string that constitutes the name of


³ the device if this font file is for a specific one.


³ The size of this member is the length of the string


³ plus a null terminating character.


bitmaps ³ Character bitmap definitions. Unlike the old font


³ format, each character is stored as a contiguous set


³ of bytes.


³ The first byte contains the first 8 bits of the first


³ scan line (that is, the top line of the character).


³ The second byte contains the first 8 bits of the


³ second scan line. This continues until the first


³ column is completely defined. The subsequent byte


³ contains the next 8 bits of the first scan line,


³ padded with zeros on the right if necessary (and so


³ on, down through the second column). If the glyph is


³ quite narrow, each scan line is covered by one byte,


³ with bits set to zero as necessary for padding. If the


³ glyph is very wide, a third or even


³ fourth set of bytes can be present.


³ Character bitmaps must be stored contiguously and


³ arranged in ascending order. The bytes for a 1-pixel


³ by 14-pixel A character, for example, are given in


³ two sets, because the character is less than 17 pixels


³ wide


³


³ 00 06 0 10 0 0 0 F 0 0 0 00 00 00


³ 00 00 00 80 40 40 40 C0 40 40 40 00 00 00


³ Note that in the second set of bytes, the second digit


³ of the byte is always zero. The zeros correspond to


³ the thirteenth through sixteenth pixels on the right


³ side of the character, which are not used by this


³ character bitmap.


Version-Specific Glyph Tables


The dfCharTable member for Windows .x has a


TGLYPHENTRY structure with the following


format


GlyphEntry struc


geWidth dw ? ; width of char bitmap, pixels


geOffset dw ? ; pointer to the bits


GlyphEntry ends


The dfCharTable member in Windows .0 and


later is dependent on the format of the glyph


bitmap. The only formats supported are


DFF_FIXED and DFF_PROPORTIONAL.


DFF_FIXED


DFF_PROPORTIONAL


GlyphEntry struc


geWidth dw ? ; width of char bitmap, pixels


geOffset dd ? ; pointer to the bits


GlyphEntry ends


DFF_ABCFIXED


DFF_ABCPROPORTIONAL


GlyphEntry struc


geWidth dw ? ; width of char bitmap, pixels


geOffset dd ? ; pointer to the bits


geAspace dd ? ; A space, fract pixels (16.16)


geBspace dd ? ; B space, fract pixels (16.16)


geCspace dw ? ; C space, fract pixels (16.16)


GlyphEntry ends


Fractional pixels are expressed as -bit


signed numbers with an implicit binary point


between bits 15 and 16. This is referred to as


a 16.16 (sixteen dot sixteen) fixed-point


number.


The ABC spacing in the following example is


the same as defined previously. However,


specific sets are defined for each character


DFF_1COLOR ; 8 pixels per byte


DFF_16COLOR ; pixels per byte


DFF_56COLOR ; 1 pixel per byte


DFF_RGBCOLOR ; RGB quads


GlyphEntry struc


geWidth dw ? ; width of char bitmap, pixels


geOffset dd ? ; pointer to the bits


geHeight dw ? ; height of char bitmap, pixels


geAspace dd ? ; A space, fract pixels (16.16)


geBspace dd ? ; B space, fract pixels (16.16)


geCspace dd ? ; C space, fract pixels (16.16)


GlyphEntry ends


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