Any contour or component can be flagged as a Mask. Mask-flagged elements subtract from the geometry that precedes them in the element order of their layer. The flag lives on the path or component itself, not on a layer, so a single layer — master, background, or helper — can mix mask and non-mask elements freely.
Mask is a design tool. The font formats — TrueType, OpenType, CFF2, UFO — have no representation for a mask flag, so masks are always flattened into plain geometry when the font is exported. Inside the glyph editor, in the FontCreator project file, and in the .glyphs format, the flag is kept and applied non-destructively, so the original masked and non-masked geometry is preserved as you authored it.
Setting the Flag
Toggle the Mask flag from the right-click context menu of the selected contour or component. A mask-flagged element is drawn with a distinct outline in the glyph editor so its role is visible at a glance.
Order Matters
Subtraction follows element order. A mask path subtracts only from the non-mask elements that appear before it in the list. Reordering elements with Bring to Front or Send to Back changes which paths are subtracted from.
Compound Shapes
Consecutive mask-flagged elements are subtracted as a single group. This is what makes a compound mask — for example a ring made of an outer path and an inner path — produce one hole rather than two separate cut-outs. Keep the parts of a compound mask next to each other in the element list and flag both as Mask.
Mask Components
A whole component can be flagged as a Mask, in which case the decomposed shape of the referenced glyph subtracts from the preceding geometry. Per-path Mask flags inside the referenced glyph also survive when the component is decomposed — manually or automatically on export — so a glyph can be designed once with internal mask paths and then reused as a component in other glyphs without losing the subtraction.
Variable Font Compatibility
Masks can make layers incompatible. After mask flattening on export, masters may end up with different point counts if their masks differ in shape between masters — the same caveat that applies to overlap removal. This is mainly important when designing a variable font: check master compatibility before shipping.
Decompose with Mask
Decompose with Mask permanently bakes mask subtraction into the authored geometry of the active layer. The masks are applied, then the Mask flags are removed from the surviving elements — leaving plain outline geometry that no longer relies on subtraction.
The font exporter applies subtraction automatically, so this command is needed only when the authored geometry itself should reflect the post-subtraction shape — for example to simplify a glyph for handoff to a tool that does not understand mask flags.
Available from Glyph → Decompose → Mask in the main menu, and from the right-click context menu in the glyph editor near the Mask toggle. Enabled when the active layer contains at least one mask-flagged element.
