FontBook initialization

When the application is started a global FontBook is instanced. During the FontBook's instantiation it will fast-parse each TrueType font in the operating system's font folder.

During the fast-parse the name, OS/2 and optionally other tables are read and then the font files are closed and memory is freed. This fast-parse is designed to be very fast to reduce impact on application startup time.

The following information gleamed during the fast-parse:

• name Preferred Font family name; code-16 if available, otherwise code-1
• name Preferred Font subfamily name: code-17 if available, otherwise code-2
• OS/2 Font weight
• OS/2 Regular/Italic
• OS/2 Serif/Sans-serif
• OS/2 Variable/Monospace
• OS/2 Regular/Condensed
• OS/2 Unicode ranges (as backup the cmap table may be parsed)
• OS/2 The height of x and H (as back the glyf table may be parsed)

Each font family is assigned a FamilyID. Each font is assigned a FontID.

There is a list of fallback font families for well known fonts, in case certain font families are not available on the system.

Each font will be assigned a list of fallback fonts for missing glyph lookup. Priority is given for fonts that start with the same font family name. For example "Arial Arabic" will be prioritized when the current font is "Arial"

Font selection

A FontVariant consists of a FontWeight+serif-flag. This allows a user to select a font family to draw a text with and emphasize fragments of the text using italic and bold.

There are a total of maximum 20 FontVariants for each FontFamilyID.

Selecting a font to render a text is done in several steps:

• A user select a font family name and a FontVariant.
• The font family name is looked up in the FontBook and a FontFamilyID is returned for a font that exists on the system which closely matches the requested family.
• The FontFamilyID + FontVariant is looked up in the FontBook and a FontID is returned for the variant the closely matches the requested variant that is available for that family.
• A grapheme + FontID is looked up in the FontBook and a FontGlyphIDs is returned. The returned FontID may be of another font than requested if the glyphs where not available in the requested fonts.

Text shaping

Features:

• Each character may have a separate text-style.
• Font fallback for characters not found in the selected font/
• Word wrapping. (UAX #14 Unicode line breaking algorithm)
• Multiple paragraph support.
• Bidirectional language handling. (UAX #9 Unicode bidirectional algorithm)
• Horizontal alignment: flush, flush-left, flush-right, centered, justified.
• Resolved paragraph language direction influences the side of alignment.
• True-Type Font kerning.
• Reverse coordinate back to index in text.
• Handle cursor movement in display-order.
• Word and Scentence selection. (UAX #29 Unicode text segmentation)

Text editing

The text-widget is used by almost every widget to draw text. This same widget is also has full capabilities for text editing.

Features:

• Insert and overwrite mode.
• Dead-key visualization, shows the character of the dead-key which will be replaced by the composed character.
• Bidirectional language support.
  • Display-order cursor movement.
  • Cursor keeps track of "current" language direction.
  • Logical-order delete & backspace.
  • Logical-order text selection.
  • Primary/Secondary; LTR/RTL cursors.
• Undo, Redo
• Copy, Cut & Paste