Fontlab Auto Kerning

[Annette Fazzari]

Adjustmetrics and kerning in a text-like editor, by planned phrases and pair lists. Apply tracking, modify widths, sidebearings and kerning globally or for selected glyphs. Automatically or manually build kerning classes and link metrics between glyphs using complex expressions. Auto-calc metrics and kerning, and audit kerning exceptions to find combinations that produce visual conflicts.

In the Metrics mode of the Glyph window, if you drag a sidebearing line or a glyph and n is larger than 1, the change in the metrics is more precise (smaller) than the distance of the dragging on screen. Hold Shift when you drag, and the change in the metrics will be the same as the distance of the dragging.

New If you turn on View > Metrics & Kerning > Spacing Controls and hover over the sidebearings in the editing modes and the Metrics mode, the Glyph window shows a cross at the intersection of the baseline and the sidebearings. This cross is now smaller.

If you want to edit metrics and kerning with your mouse, use Preferences > Spacing > Metrics lines to set the transparency to around 4%, and the spacing controls (sidebearings and the cross) will be barely visible. Also, in the Glyph window sidebar, set a higher linespacing to increase the distance between the baseline and the spacing controls.

Bounding box mode: If View > Metrics Line is turned off, the sidebearing text boxes in the Glyph panel, in the Metrics table and in the Glyph window property bar show sidebearings at the bounding box, calculated using all elements except the elements that are set to Nonspacing.

Metrics line mode: If you turn on View > Metrics Line, the background of the text boxes becomes violet, and the sidebearing values are calculated at the intersection of the Metrics line and the glyph content (excluding Nonspacing elements). Drag the dotted violet guide in the Glyph window to set the Metrics line position for the current master.

New If View > Metrics and Kerning > Spacing Controls is turned on, and if Preferences > Grid, Guides and Hints > Font guide opacity is higher than 50%, the Metrics line now explicitly shows the sidebearings (thick bars and numeric values) on the glyph canvas.

To hide them, move the Preferences > Grid, Guides and Hints > Font guide selector to the left half of the slider. You can also use the slider to generally make the inactive Metrics line (and the font guides) more or less visually subtle.

If you have View > Metrics & Kerning > Spacing Controls turned on, the Glyph window canvas shows the numeric sidebearing values at the bottom of the current glyph in Metrics mode, and also in other Glyph window modes if Preferences > Spacing > Spacing controls show sidebearing values in editing modes is turned on.

New If you choose Set equal to and turn on Use the metrics line, FontLab will apply the new sidebearing value at the intersection of the glyph content and the metrics line, regardless of whether the Metrics line is visible in the Glyph window or not.

New With the new Tools > Actions > Metrics > Remove metrics links action, you can remove all metrics links (expressions) from the specified glyphs and layers, so the sidebearings and widths become simple numerical values. #5578

In the Glyph window, if you tap the ; key (except in Kerning mode), FontLab will automatically calculate the sidebearings for the current glyph. New With Font > Metrics > Auto Space, you can also do it for a Font window selection.

If you have multiple glyphs in your Glyph window, you can use Text > Change Case or the buttons at the top of the Glyph window sidebar to change the case of the text between UPPER CASE, lower case, and New now also Title Case.

In the Kerning mode of the Glyph window, if you drag a glyph and n is larger than 1, the change in the kerning is more precise (smaller) than the distance of the dragging on screen. Hold Shift when you drag, and the change in the kerning will be the same as the distance of the dragging.

If you turn on Preferences > Spacing > Inactive kerning pairs are editable and you turn off View > Show > Spacing Controls, you can rapidly make small kerning changes to all pairs that are part of the current Glyph window text.

If you turn on Preferences > Spacing > Hide cursor while editing kerning, and you drag a kerning pair in the Kerning mode of the Glyph window, FontLab temporarily hides the pointer during the dragging, so it does not obscure your view.

New Click the Auto-kern button in the Pairs & Phrases panel to autokern the selected pairs using the new FontLab K2 autokerning algorithm, or tap ; in the Kerning mode to use K2 to autokern the current pair.

FontLab has a few places where you can edit the kerning class assignment for a glyph: in the Glyph panel, and in the Font window status bar. New By default, the UI arranges the kerning class assignment boxes by the design side similarity of the glyphs, analogically to sidebearings, but you can change this arrangement.

The new default layout is decidedly glyph-centric. The class kerning fields are located at the side that corresponds to the side of the glyph which is similar to other glyphs in the same kerning class.

If you create a new left kerning class, you cannot create a new right kerning class that has the same name, and vice-versa. Therefore, we recommend that you use a consistent naming scheme for your left and right kerning classes, for example L_A for the left class that groups A and glyphs that are similar on the right side, and R_A for the right class.

The kerning class fields in the Font window status bar only show kerning class assignments for the current glyph. The fields in the Glyph panel can show kerning class assignments for multiple glyphs that are selected in the Font window, and you can assign all selected glyphs to the same class in one go.

Since both glyphs belong to a kerning class, the AY pair that you see in the window represents the potential class-to-class kerning pair: @A @Y. In other words, the A glyph in the text represents the @A class, and the Y glyph represents the @Y class.

For all glyph combinations in all or the selected class pairs of the current master, FontLab will check if the smallest horizontal distance between the contours of both glyphs of the combination is less than the threshold. If FontLab finds any such combinations, it opens the Audit Kerning Exceptions dialog.

If you choose Add exceptions in the dialog, FontLab creates the new kerning exceptions and sets each kerning value so that the smallest horizontal distance between the contours of both glyphs is equal to the threshold.

Select pairs or phrases in the Pairs & Phrases panel, Cmd/Ctrl-click the Auto button in the panel, and in the Kern to Distance dialog, specify the distance. FontLab will add or change the kerning value so that the smallest horizontal distance between the contours of both glyphs of the pair is equal to the specified distance. A negative value means that the glyphs may overlap by the specified amount.

OpenType fonts store kerning in GPOS table lookups. Each lookup for horizontal kerning has a flag that specifies the writing direction of the kerning pairs: left-to-right (LTR) or right-to-left (RTL).

Scripts that use the same writing direction may store kerning in the same lookup or in separate lookups. For example kerning for LTR scripts like Latin, Cyrillic and Greek may be stored in just one lookup. But kerning for RTL scripts like Arabic and Hebrew may not be stored in that same lookup, and needs a separate lookup that has the lookupflag RightToLeft enabled.

Kerning for scripts that use the same writing direction may be split into multiple lookups, each having the appropriate flag, but kerning for scripts that use different directions must not be mixed within one lookup.

In Unicode, only some characters are associated with just one writing direction: Latin letters are always LTR, and Hebrew letters are always RTL, but digits or punctuation signs may be used in either direction.

New If you open files in .glyphs 3 format, FontLab converts the RTL pairs (stored in the kerningRTL key) from logical to visual order. If the same visual pair is defined in both LTR and RTL .glyphs storage, FontLab favors the LTR pairs.

New If you export files into .glyphs 3 format, FontLab converts applies heuristics to determine which pairs are RTL, converts them from visual to logical order and stores them in the RTL .glyphs 3 storage.

In late 2022, the topic was widely discussed among font technology professionals. The majority agreed that visual order is more predictable and easier to handle, especially for glyphs representing characters with weak and neutral directionality type.

New If you turn on Text > Right to Left, FontLab will perform a live on-the-fly reversal of the Glyph window text, so the input text will be shown in the right-to-left order. This is independent of the script of the text: if you enter the text TYPO and turn on Right to Left, the Glyph window will show OPYT, and if you turn Right to Left off, the window will show TYPO.

The Glyph window and the Kerning panel display the pairs in visual order. The left side of a pair always shows the glyph or class that will be visually on the left side in typeset text, and the right side of the pair shows the visually right glyph or class.

If you have a font that has kerning for scripts that run in different horizontal directions, and you export it into OpenType, FontLab will produce two kerning lookups: one for left-to-right and one for right-to-left. If you export the font into other formats like .glyphs or UFO, FontLab will export the right-to-left kerning in the most suitable form for the format.

To set the line edges in a more visually pleasing way, glyphs in a font can optionally have two additional margins, called optical bounds. These margins are intended to be used if a glyph is the first or last in a line. The optical bounds are usually much tighter than sidebearings. In OpenType, optical bounds are realized through the lfbd (left bounds) and rtbd (right bounds) features, which subtract a define distance from the sidebearing.

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