AMIGA FONTS 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. OUTLINE TYPEFACES 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. OTAG SPECIFICATION EXAMPLE 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 handle. 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. DISKFONT USE OF OTAG ENTRIES 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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