Composite and Auto Glyphs»
In FontLab VI, glyph drawings exist on each layer separately. So in this context, when we say glyphs we are, in fact, talking about glyph layers. It is important to understand that a glyph can be simple in one layer, and composite or auto in another layer.
Based on how they are constructed and what kind of elements they are made up of, glyphs in FontLab VI can be classified into three categories:
A simple glyph consists of one simple element — either a set of contours or an image. If the glyph has a contour element, it has a simple black fill, no stroke, no element-level transformation and is not referenced anywhere else in the font. Such a glyph can be created using FontLab’s vector drawing tools, and will be natively exported into common font formats. If the simple glyph is made up of an image, it will be exported into bitmap-based color font formats. In either case, a simple glyph can contain anchors as well as other objects, which are not included in the common exported font formats, such as glyph guides and stickers.
A composite glyph consists of multiple simple or compound elements. Each of these elements can be manually added, removed or positioned; and element-level transformation can be applied to them. In a composite glyph, constituent elements can also be references. If you try to edit an element reference, depending on whether it is locked or not, either its original (or primary) version will open for editing or you’ll be able to edit it in place. Remember that in both cases, the changes you make to the element reference will be propagated across the font because it is linked to references in other glyphs. In a composite glyph, glyph guides, anchors, advance width and sidebearings are all independent of any element references it might contain.
If a composite glyph contains only locked references, it works like a composite glyph in TrueType-flavored OpenType, FontLab VFB or UFO fonts.
An auto glyph is an “automatic composite glyph”, which is generated automatically from predefined recipes. It contains components, i.e. references to primary glyphs, and is updated automatically whenever you change the contours, element positions, anchors or metrics in any primary glyph. An auto glyph also inherits its advance width and sidebearings from its components.
You cannot manually add or remove the contents of an auto glyph, only provide a custom recipe that tells FontLab how to generate it. To manually edit the elements in an auto glyph, you need to convert it to a composite glyph.
When you export a font into the OpenType TT, VFB or UFO format, FontLab tries to transform its composite and auto glyphs into composite glyphs suitable for that format. When you export into OpenType PS format, FontLab will use composite glyphs for CFF subroutine compression. Composite glyphs may also contain bitmap color images or SVG images that can be exported to Font Formats that support color glyphs.