SwiftTrueTypeFont

Pure-Swift reading of the True Type Font (.ttf) file format, and conformance to SwiftGraphicsCore's Font.

This is a work in progress. The TrueType / OpenType font specs are massive, https://docs.microsoft.com/en-us/typography/opentype/spec/otff,https://developer.apple.com/fonts/TrueType-Reference-Manual/RM05/Chap5.html#FDEF.

For users:

Read a .ttf file

import SwiftGraphicsCore
import SwiftTrueTypeFont
let data:Data = ... //read data from a *.ttf or *.otf file.
let trueTypeFont:TrueTypeFont? = try? TrueTypeFont(data:data)

Rendering a font

TrueTypeFont comforms to SwiftGraphicsCore's Font, which means that in order to render it, you have to provide values for the options. In particular, you need to provide an option value for the size in order to obtain a RenderingFont. Only a RenderingFont can make glyphs directly.

Here's an example of getting a rendering font with size 14.0 from the font.

let font:Font = trueTypeFont
let values:[FontOptionValue] = font.options.compactMap({ option in
        guard option.name == String.FontOptionNameSize else { return nil }
        return option.value(14.0)
	})
guard let renderingFont:RenderingFont = font.rendering(options:values) else { /* fail */ } 

The rendering font can then be used with the drawText( method on any GraphicsContext.

Getting the PostScript name of the font, suitable for use in UIFont(name:... in iOS.

let name:String? = font.postScriptName

For developers

Conveniences for reading MSBs from Data are in Data+MSB.swift

Feel free to contribute; I'm a stickler for making things "Swifty", because I love Swift as a language. Any functions you write should feature two paths: a detailed path suitable for introspection and throw errors meaningful to a developer who wants to examine the validity of the font, and a simple path that gets a font user quick access to things they want.

Progress

Name

• ☑ Post script name in English
• ☐ other names in other languages

Glyph/path conversion

• ☑ Simple Glyphs
• ☑ Compound glyphs (tested super-simple transformations, haven't tested point-matching offsets)
• ☑ Modify fill algorithms in SwiftGraphicsCore to support winding number logic & wrench down tight the intersection algorithms.
• ☐ Non-outline glyphs

Character Maps

Currently cmap formats 0, 4, 6 and 12 are supported.

I don't plan to support format 2 because it only supports mixed 8/16-bit encodings directly, and we're getting the utf-8 byte stream after the multi-byte encodings have been flattened.

I don't plan to support formats 8 or 10 because their use is very rare.

I don't plan to support 13 because I don't plan to support "last resort" fonts, but maybe that will change.

I don't plan to support 14 because I don't plan to support variation sequences.

Recognized Encodings

• ☑ Unicode 2.0+ encodings
• ☑ Windows UCS-2 encoding
• ☐ other character encodings on other platforms as a fall back?

Variations

• ☐ fvar table
• ☐ gvar table

Instructing

(Instucting cannot be activated until all instructions are correctly interpretted)

• ☑ procedural, logical, and arithmetic operators except if/else
• ☐ geometry commands
• ☐ CVT / storage commands