Boolean Assembly: Fusion, Clipping, and the Fill Tool
A glyph can remain a collection of editable shapes while displaying their combined outline. Fusion lets you choose how stacked elements combine. The Fill tool lets you choose the solid and hollow regions directly on the canvas.
The Fusion Filter
Fusion performs live Boolean operations between elements. Unlike a contour-level Boolean operation, it does not require you to combine the participating contours into one ordinary element and immediately replace their geometry.
The element carrying the Fusion operation is the fusor. It acts on the fused elements below it in the construction's stacking order. FontLab places the participating content in a Fusion group, which computes the combined result. Elements above a fusor are not cut by that fusor.
The front/back operands selected explicitly in Overlaps and Boolean Operations are determined here by element stacking order. That order therefore determines more than appearance. A subtracting rectangle below a letter cannot perform the same job as that rectangle above the letter. Inspect the Elements panel when a result affects the wrong shapes.
Choose the operation
| Fusion type | Result |
|---|---|
| Add | Keeps the combined filled area and removes internal overlaps. |
| Subtract | Cuts the fusor's area out of the content below it. |
| Intersect | Keeps the area shared by the fusor and the content below it. |
| Exclude | Keeps the areas that do not overlap; shared areas become hollow. |
Add is the live counterpart of removing overlaps. Subtract makes a cutter. Intersect makes a clipping mask. Exclude is useful when the overlap itself should become negative space.
Make a live cut
Start with only the intended participating shapes. Applying Fusion can gather other elements into the construction, so check the glyph’s element list before beginning.
- Put the body and cutter in separate elements in the same glyph layer.
- Use the Elements panel or Element > Arrange commands to place the cutter above the body.
- With the Element tool, make the cutter current.
- Choose Element > Fusion > Subtract.
- Move or reshape the cutter and inspect the changing cut.
The same menu provides Add, Intersect, and Exclude. You can change the operation after applying it. The Element tool's context menu and Fusion controls provide additional access.
The element operation menu distinguishes Add, Subtract, Intersect, and Exclude from None. Check the chosen operation when assembling live geometry.
After applying Fusion, examine the construction’s contents in the Elements panel before adding further operations. Within that construction, reorder elements to change which content falls below a fusor. You can also edit the participating elements individually without combining their source contours.
If you apply Fusion from a contour selection, FontLab can separate that selected contour content into an element first. Expect the element structure to change even though the resulting Boolean operation remains live.
Finish or discard the construction
Use Element > Expand Filters on the Fusion construction when you want its calculated result as editable contours. Choose Element > Remove Filter to expose the participating source elements without the construction. To stop one element acting as a fusor while retaining the surrounding structure, set its Fusion operation to None.
Fusion also works with components. Export resolves the Boolean result into the final outline as required, including constructions involving scaled or variable components. Fusion can therefore require decomposition at export even when the source components do not visibly overlap. Retain the native source if you need to preserve the reusable construction.
After changing stacking order or the cutter's shape, inspect small regions and counters in a filled view. An unintended sliver may be hard to notice while the source outlines are visible.
The Clipping Group
A Clipping Group is the older clipping construction available through Element > Make Clipping Group. With the intended elements selected, the topmost element acts as a mask for the combined content beneath it. A patterned rectangle under a letter-shaped mask, for example, produces a pattern confined to the letter.
The result serves the same design purpose as Fusion's Intersect operation. Prefer Fusion for new work: it provides union, subtraction, intersection, and exclusion in one construction model. Recognize Clipping Groups when editing existing files: their source shapes remain part of the construction and the clipping result can be expanded into contours.
The Fill Tool
The Fill tool chooses which enclosed regions are solid or hollow. It does not assign a stroke width or turn a skeleton into a stroked outline.
Press F to activate it. Hover over an enclosed region and inspect the highlight, then click to fill that region or Alt-click to make it hollow. Repeat for each region you want to change. Holding F temporarily accesses the tool; releasing it returns to the previous tool.
The tool chooses its mechanism according to the geometry. With simple, non-overlapping contours, it can reverse a contour's direction without creating a filter. With overlapping contours, it can create a live Fill filter, preserving the source contours and calculating the chosen regions from their arrangement.
For a straightforward counter, such as the inside of an O, use Reverse Contour when direction is the only issue. Reserve a Fill construction for regions formed by more complex overlaps, where selecting the desired areas is easier than specifying a sequence of Boolean operations.
Shift-click with the Fill tool reverses one contour's direction directly. This is useful when you already know which contour needs reversal and want to work on the canvas.
Fill across several elements
The Fill tool normally works within one element. For regions formed across separate elements, group those elements first. Use ordinary contour elements or element references; convert components with Element > Reference > Component to Reference before using this workflow.
To make a transparent letter inside a solid disc:
- Use Element > Reference > Add Reference… to add the disc and the letter as element references.
- Position and size them so that the letter fits within the disc.
- Select both with the Element tool and choose Element > Group.
- Make the group current and activate the Fill tool.
- Alt-click the letter's regions to hollow them, checking each highlighted area before clicking.
Check the letter's counters as well as its main strokes. The tool applies a choice to a region; it does not infer a complete inverted alphabet from one click.
Edit a Fill construction
You can continue changing the source contours while the filter is live. However, a fill choice depends on the regions formed by their arrangement. Moving contours apart and then back together can require you to choose the regions again. Recheck the result after a structural edit, especially when a previously enclosed region opens or splits.
Use Element > Expand Filters to turn a completed Fill construction into ordinary contours, or Element > Remove Filter to discard it. If no filter was created because the tool only reversed a contour, undo or reverse that contour again to restore its direction.
A Fill construction is a different way of specifying a Boolean result: Fusion starts with the operation and stacking order; Fill starts with the areas you want to keep or remove. For a design with several masters, check those areas in each master and between them. An overlap arrangement that changes during interpolation can change the regions available to the filter.