mirror of https://github.com/neutrinolabs/xrdp
88 lines
3.2 KiB
Plaintext
88 lines
3.2 KiB
Plaintext
The fv1 font format has the following characteristics:-
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1) Bitmap fonts (i.e. pixels are on or off)
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2) 96 DPI is assumed
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3) Glyphs from U+0020 up to a pre-defined limit are stored in the file.
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At the time of writing this limit is U+4DFF. To change the limit
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requires a change to xrdp/xrdp_types.h and (potentially)
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fontutils/mkfv1.c
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4) Font format is header, plus a variable data area for each glyph.
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The intention (over time) is to build support for the freetype2 library
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directly into xrdp. This will allow for modern font features like
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anti-aliasing and kerning to be supported.
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General Info
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------------
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All numeric values are 2 octets, and stored in twos-complement
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little-endian format.
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Dimensions are all measured in pixels.
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Font header
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-----------
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signature 4 octets File signature - "FNT1"
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font~name 32 octets Null-terminated if less that 32 octets long
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point_size 2 octets Assumes 96 DPI.
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style 2 octets Unused. Set to 1.
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body_height 2 octets Line spacing for font.
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min_descender 2 octets The common lowest descender value in the font
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glyphs (A few glyphs may be lower than
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this). Used to calculate where the font baseline
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is in relation to the text box for the font.
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<padding> 4 octets Set to zero.
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Older fonts, generated for xrdp v.0.9x and earlier, have zero values
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for the body_height and min_descender. For these fonts, the body height is
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calculated as (-baseline + 1) for the first glyph, and the glyphs are
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all offset so that a min_descender of 0 works OK.
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Glyph data
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----------
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The header is followed by a number of glyphs representing U+0020 upwards. The
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glyphs have a variable size. The format of each glyph is as follows:-
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width 2 octets Width of character data
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height 2 octets Height of character data
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baseline 2 octets Offset from font baseline to 1st row of glyph data
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offset 2 octets Space before glyph is drawn (can be -ve)
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inc_by 2 octets Total width of glyph + spacing. The width of
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a string is obtained by adding up all the inc_by
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fields for all the glyphs
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data <variable> Bitmap data.
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Bitmap data is laid out in rows from top to bottom. Within each row the
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most significant bit of each octet is on the left. Row data is padded
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to the nearest octet (e.g. a 14 bit width would be padded by 2 bits to
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16 bits (2 octets). The total data is padded out with between 0 and 3
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octets to end on a 4-octet boundary.
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Example glyph:-
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Glyph : U+0067
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Width : 12
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Height : 18
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Baseline : -13
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Offset : 1
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Inc By : 15
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Data :
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-13: ...XXXXX..XX 1F 30
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-12: ..XXXXXXXXXX 3F F0
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-11: .XXX....XXXX 70 F0
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-10: XXX......XXX E0 70
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-9: XX........XX C0 30
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-8: XX........XX C0 30
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-7: XX........XX C0 30
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-6: XX........XX C0 30
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-5: XX........XX C0 30
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-4: XXX......XXX E0 70
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-3: .XXX....XXXX 70 F0
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-2: ..XXXXXXXXXX 3F F0
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-1: ...XXXXX..XX 1F 30
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+0: ..........XX 00 30
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+1: .........XXX 00 70
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+2: ..X.....XXX. 20 E0
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+3: ..XXXXXXXX.. 3F C0
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+4: ...XXXXXX... 1F 80
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