Many shapes in a digital font are repeated identically across glyphs. These repeated elements can be turned into components. Components are reusable parts stored as separate glyphs which can be borrowed to form another glyph. For example, the letter é is made of the combination of two components; the base letter e and the acute accent.

Using components instead of copying contours keeps shapes consistent and helps reduce the font file size.

• A glyph made only of components is called a composite.
• A glyph that combines both contours and components is called a mixed composite. Mixed composites are not permitted in the final binary font (exported font) files. As a result, they are usually decomposed during export.
• When a component references another component, it is said to be nested.
• A component is considered as aligned when it is reused in a glyph without transformation.

For design purposes, components can be transformed — shifted (translated), scaled, rotated, skewed, flipped, or mirrored. Transformed components may need to be decomposed, especially if the transformation alters the contour direction (such as mirroring), which can affect its appearance on the pixel grid.

FONT ENGINEERING ADVICE

The component system is a compression strategy used in TrueType fonts to reduce file size by referencing repeated shapes across glyphs. In contrast, PostScript-based fonts (OpenType-CFF flavor, with the .otf extension) use a different space-saving method called subroutines—small sections of path instructions that can be reused. Because subroutines operate at the path level rather than referencing entire glyphs, components are typically decomposed during export so their outlines can be stored and reused within these subroutines.