Filters, Strokes, and Brushes under Variation

A live construction can look correct in every master and still produce unsuitable geometry between them. Check both its editable inputs and the resolved outline that the intended output needs.

Keeping Filtered Elements Compatible

While a filter remains live, the varying inputs are its stored base content and supported per-master parameters; expansion or export resolves generated outlines. Start with corresponding source content. Each master should contain the intended counterpart of an element, its contour structure, and the compatible construction applied to it. Keep the order and role of filters consistent when they are meant to participate in one varying design.

Some filter settings are numeric and can vary; others choose an operation or construction type. A radius and a choice between subtraction and intersection are not the same kind of parameter. Do not assume that every filter configuration has a meaningful continuous blend merely because its controls remain editable.

A useful check has two stages:

Preview the live construction through the actual designspace, including combined-axis locations.
On a duplicate source, resolve representative results and compare the contour structures needed for the intended output.

Check contour and node counts, segment types, order, direction, and start points. Also inspect disappearing regions, tiny contours, and changing intersections. A Boolean operation can change topology as its inputs move, even when those inputs have compatible source nodes.

Smart Corners need the same care. Rounded-corner construction retains useful structure in some zero-radius and adjacent-corner cases, but a rounded corner and an ink trap do not universally expand to the same two-node structure. Ink traps can include additional notch and transition geometry. Keep corresponding treatments aligned and inspect the resolved results.

Expanding only one source master can replace an editable filter construction with a different structure from the remaining masters. If you decide to work with resolved contours, make that transition deliberately across the relevant sources and match the results afterward.

A successful live preview is valuable evidence about the current editor state. It does not establish that every export route preserves the same editable filters or produces interpolation-compatible resolved outlines. Keep the native source while checking the actual output you intend to deliver.

Copying Deltas across Masters

The Delta filter's property bar provides Copy to masters, with choices for all compatible masters or only visible masters. This copies the correction construction to corresponding content; it is not a global copy of every filter in the font.

Before copying, check that the target layer structures match and that the corresponding element occupies the intended structural position. The operation relies on compatibility and element correspondence. Similar-looking drawings in differently organized layers are not a sufficient basis.

To reuse a correction:

Finish the Delta adjustment on the current source and inspect it at full and reduced progress.
Check the other masters' compatible source elements.
Choose the copy-to-masters scope in the Delta controls.
Inspect each affected master, including its filter nesting and adjusted outline.
Preview between the masters again.

Copying a delta does not decide that its amount is optically suitable in every master. A correction useful in a heavy source can need a different amount in a light one. Avoid repeatedly applying the copy operation without checking whether a target already contains a corresponding filter construction.

A sparse Delta construction can instead keep its base geometry shared. For example, suppose an Ascender axis has Regular and Tall masters, and only selected glyphs need a separately adjusted tall construction:

Work on a saved source and open h in its Regular layer.
Prepare the Tall layer destination; preserve any existing Tall drawing before replacing it.
Option/Alt-click Duplicate layer in Layers & Masters to create a layer whose element references Regular's geometry.
Name the new layer Tall so it corresponds to that master.
Apply Element > Add Filter > Delta and raise the ascending strokes while attaching positions that should stay fixed.
Edit the Regular source and inspect Tall: the shared base changes, with the Delta adjustment applied on top.

This pattern preserves a live relationship to the base rather than making an unrelated copy of an interpolated outline. Check the shared element, delta, and intermediate results after changes. Use the sparse construction only for glyphs that need it; do not replace satisfactory independent master drawings without a design reason.

Strokes and Brushes across Masters

For skeleton-built forms, establish compatible paths before varying their visible body. Keep corresponding skeleton nodes and contour directions, then use supported per-master stroke or brush settings to describe the weight and contrast changes.

For strokes, the Thickness tool modulations are per-master values. Their skeleton nodes must correspond across masters; see The Thickness Tool. Compare thickness, side distribution, caps, joins, and those local values. A cap-type change is a discrete choice, and a miter can change its resolved shape when it crosses its limit. Neither should be treated as an ordinary scalar transition without checking the result.

For Power Brush, compare the element nib and local size, angle, and roundness overrides. Corresponding modulation nodes need to represent the same design locations. Adding a local override at one arbitrary node without a counterpart makes the intended progression harder to control.

A practical sequence is:

Make the skeletons correspond and inspect their interpolation without relying on a thick envelope to hide problems.
Establish a consistent stroke or brush construction in the source masters.
Set the element-wide parameters for each design.
Add corresponding local modulation where the form needs it.
Inspect live intermediates and resolved outline structures, then test the intended export.

Thickness can carry much of a weight change, but it cannot automatically correct every counter, join, or spacing relationship. Adjust the skeleton where its path must change too.

Brush expansion can create different outline structures as the nib and path change. Stroke expansion also depends on joins, caps, and intersections. Do not assume a constant output node count from the number of skeleton nodes alone.

Keep source and output decisions separate. A live construction remains useful for designing static instances even when it needs additional work before it can supply compatible outlines for a variable font. Retain the editable version and resolve or redesign only the parts that the output requires.