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The existence of a disk font is indicated by the existence of
its associated font contents file, whose name has the suffix
".font". It is this name that is used in the actual font
open call of the application. Amiga fonts are collected in
the directory path(s) associated with the FONTS: assign. It
is this assign that is searched if no explicit path name is
provided in the font open call: use of an explicit path is
generally discouraged. The actual bitmaps of traditional
Amiga fonts are stored in a directory with the name of the
font contents file stripped of its ".font" suffix. This
directory is usually in the same directory as the font
contents file. This traditional arrangement is supported by
the FixFonts system application.
For example:
o FONTS: is assigned to Sys:Fonts/
o Sys:Fonts/garnet.font exists and describes that the
font "garnet.font" exists
o Sys:Fonts/garnet/ contains the bitmap images for
sizes 9 and 16
Other variations of file placement may exist, but they
require custom tools to maintain -- tools available not from
Commodore, but from other sources such as Fish disks.
Font contents files are flagged with magic numbers that not
only verify that they are a font contents files but also what
variation of file structure they contain.
The existence of an outline typeface is indicated by a magic
number in the font contents file. They are further described
in the associated outline typeface tag file, whose name is
the that of the font contents file with the suffix ".otag"
substituted for ".font". This tag file contains a tag list
that is to be processed and passed to the outline engine
(i.e. bullet.library) in order to select the associated
typeface. It also contains information applications may use
to guide their use of the typeface.
Here are the steps necessary to go from an arbitrary font
name into an environment where glyphs from that font
can be accessed:
1. Read the header from the font contents (.font) file and
verify that the magic cookie fch_ID is OFCH_ID.
If it is not, then this is an Amiga bitmap font,
not an outline font.
2. Read the associated outline tag (.otag) file into memory:
a. Validate that the OT_FileIdent exists and matches the
file size.
b. Allocate a memory buffer and read the file into it.
c. Resolve addresses: for each tag with the OT_Indirect
bit set, add the memory buffer origin to the
associated data.
3. Find the OT_Engine tag and ensure that you have the
proper engine open:
a. If you already have an engine handle for this engine
name, you skip these steps.
b. append the suffix ".library" to the engine name.
(e.g. "bullet" becomes "bullet.library").
c. use exec's OpenLibrary() to open the library.
d. use the engine's OpenEngine() to acquire an engine
4. Pass the full path name of the .otag file to the engine
with the OT_OTagPath tag using SetInfo().
5. Pass the memory copy of the .otag file to the engine with
the OT_OTagList tag using SetInfo(). This step may be
combined with step 4, passing first the path then the
list in one call.
The library is now ready to accept glyph metric information
(e.g. size and glyph code) and produce glyph bitmaps.
The diskfont library uses other entries from the outline tag
(.otag) file. The following are used both during inquiry of
what typefaces exist (AvailFonts) and during creation of an
Amiga TextFont (OpenDiskFont):
o OT_IsFixed is used to determine whether these outlines
describe a PROPORTIONAL flagged font.
o OT_StemWeight is used to determine whether these outlines
describe a BOLD style font.
o OT_SlantStyle is used to determine whether these outlines
describe an ITALIC style font.
o OT_HorizStyle is used to determine whether these outlines
describe an EXTENDED style font.
The following are used only during OpenDiskFont:
o OT_YSizeFactor is used to convert the Amiga pixel height
specification, which describes the distance from the
lowest decender to the highest ascender, into a point
size specification, which is related (via YSizeFactor)
to a nominal character height.
o OT_SpaceWidth is used as the width of the space character.
The following is used only during AvailFonts:
o OT_AvailSizes is used to generate a list of sizes
available for the font.


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