hairetsu ~i2d08

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<img src="hairetsu.png" alt="NuMem" style="height: 50%; max-height: 512px; width: auto;">

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Rendered with Hairetsu using Noto Sans JP

Hairetsu

Hairetsu (配列 /haiɾetsɯ/, sequence/arrangement in Japanese) provides cross-platform text lookup, shaping and rasterization with plans for complex text layout and bidi in the pipeline.

Hairetsu is built around reference counted types built ontop of numem; despite this the types provided by hairetsu should be usable in a GC context.

Enumerating System Fonts

Hairetsu has a subsystem for enumerating fonts on the system and their capabilities. To facilitate this, Hairetsu provides "collections". Collections cover fonts and their variants.

You can get a collection of all fonts that the OS is aware of by calling FontCollection.createFromSystem, this function will only list fonts which Hairetsu can realize to actual font objects and will omit non-realizable fonts.

For example, to select the first font that supports a given unicode code point, you can use FontFamily.getFirstFaceWith to query each face in the collection for a UTF-32 character.

FontFaceInfo's can be realised to their font file using FontFaceInfo.realize; some fonts might not be realizable. Use FontFaceInfo.isRealizable to query this.

// Note:  You can pass in a boolean to tell Hairetsu whether to ask the OS
//        to reindex its font list.
FontCollection systemFonts = FontCollection.createFromSystem();
FontFile selectedFont;
foreach(family; systemFonts.families) {
    if (FontFaceInfo face = family.getFirstFaceWith('あ')) {
        selectedFont = face.realize();
        break;
    }
}

NOTE

This will only work on systems where a backend is implemented; otherwise you will get an empty collection.

Loading Fonts

Hairetsu includes its own font reading and rendering mechanism, to load a font you first create a FontFile instance. A couple of convenience functions are provided to do this.

Font Files are the top level object of Hairetsu's font ownership hirearchy; ownership is managed internally by hairetsu, as such you should not attempt to manually destroy objects unless the documentation tells you to.

From these font files you can create Font objects, which represent the logical font within a font file container, some containers can contain multiple fonts within a single file, such as TTC containers.

FontFile myFile = FontFile.fromFile("notosans.ttf");
Font myFont = myFile.fonts[0]; // Gets the first font within the file.

writeln(myFont.type, " ", myFile.type); // Likely would print "TrueType SFNT"

Looking up glyphs

Generally you should refer to a text shaper to find glyph IDs for your target language, but Hairetsu does provide the essentials for looking up glyphs by character, however this will be without substitutions unless you write code to fetch those.

A CharMap is provided by fonts which allows looking up glyph indices from eg. the CMAP table in TTF and OTF fonts. If a font does not contain a glyph for the given character code, the .notdef glyph index will be returned instead, a convenience GLYPH_MISSING enum is provided to help you check this case.

GlyphIndex i = myFont.charMap.getGlyphIndex('あ');

Faces

When using a font it's often desired to be able to configure properties about the font without needing to repeatedly reload a font to do so; the FontFace facilitates this by being a type which refers back in to the parent font that created it.

This allows you to, for example, set style, sizing, hinting requirements, etc. for the glyph data you wish to fetch from the font. You can have as many font faces loaded at a time as you want.

// Create a font face, scaled to half of the base size.
FontFace myFace = myFont.createFace();
myFace.scale.x = 0.5;
myFace.scale.y = 0.5;

Acknowledgements

Language tag mapping is based on the map table created by jclark.

https://github.com/jclark/lang-ietf-opentype

Some inspiration has been taken from various renderers, such as fontdue, canvas_ity and others. The glyph rendering algorithm is more or less an amalgamation of them all, with smaller tweaks, using signed converage masks (note; NOT SDFs) to effectively render glyphs.