Visual TrueType Instructions

Build a program from a few reliable controls. Establish alignment points, control important distances, interpolate secondary points, and use size-specific deltas only where the broader instructions do not produce a satisfactory result.

The Instruction Set

FontLab's visual tools provide Align, zone alignment, Single Link, Double Link, Interpolate, Middle Delta, and Final Delta operations. Select X or Y deliberately: a command controls the corresponding coordinate direction.

The TrueType Hinting property bar collects the instruction tools and preview controls used during visual hinting.

Alignments and links establish touched points. Interpolation uses controlled references to place another point. Middle deltas can affect the later interpolation of untouched points, while final deltas make a correction after that pass.

For component-only layers, prepare the source glyphs’ instructions, which supply the component hinting route. To author an independent visual program on a resolved host, deliberately decompose a saved copy first. Use the ordinary contour-layer workflow described in The TrueType Hinting Model and Workspace and recall the source/content markers in Font Window Anatomy.

Alignment Instructions

Align establishes a point on the grid. Its rounding choices include nearest grid line, the lower/left line, the upper/right line, a pixel center, and the nearest half-grid step.

Select the Align tool, choose the instruction direction, and click the point. Inspect the resulting instruction and choose its rounding method in the options. Use an alignment that supplies a meaningful reference for subsequent links rather than aligning every point independently.

AlignTop and AlignBottom use named TT zones in the vertical direction. A point inside a suitable zone can receive the corresponding zone alignment; a point outside those zones can instead receive a free alignment. Check which command was created and which zone it names.

The shared setup rounds the zone reference for the current size, and the glyph instruction uses that reference under its alignment rules. Merely moving the source point near a zone is not proof that the program now contains the intended zone-linked command.

Link Instructions

A Single Link places a destination relative to a base point. Select Single Link, click the base and then the destination, or drag from the base to the destination. If the base is not yet touched in that direction, FontLab adds an alignment for it. The distance can use a named standard stem, rounded outline distance, or an unrounded distance.

A Double Link establishes a stem relationship between two points without requiring one to be a previously fixed base. Select Double Link and drag from one of the two points to the other. The blue line with two arrows identifies the resulting relationship. Both points become touched in the instruction direction. It controls the distance more directly than their absolute placement, so check the surrounding alignment when using it to start a chain.

A Smart Link provides stem-adaptive linking. Inspect the actual stem association it selects; its name does not establish that it chose the most useful standard for every design.

The placement modifiers provide these variants:

Tool/modifier	Intended variant
Single Link, no modifier	Connects to a detected standard stem, or uses a rounded distance if no stem matches; no separate destination alignment.
Single Link, Shift	Not connected to a named stem.
Single Link, Alt	Aligned destination with stem connection.
Single Link, Shift+Alt	Aligned destination without named-stem connection.
Single Link, Control	Unrounded distance.
Single Link, Control+Alt	Unrounded-distance variant with destination alignment.
Double Link, no modifier	Connects to a detected standard stem, or uses a rounded distance if no stem matches.
Double Link, Shift	No named-stem connection.
Double Link, Control	Unrounded distance.

Inspect and refine the resulting instruction in its options instead of relying solely on the gesture. Round length and Align destination are alternative controls where the options make them mutually exclusive. Reverse a link or change its type only after checking which point supplies the reference.

The Single Link options expose the distance treatment and stem association. The shown Stem: None is an example state; inspect the association required by your program.

Interpolation Instructions

An Interpolate instruction keeps a point's relative position between two references as those references move under hinting.

Select Interpolate, then click the first reference point, the point to interpolate, and the second reference point. FontLab stores the middle click as the target and the other two as its references. Check the displayed connections, particularly when the points are close together.

Use references whose positions have already been established. Otherwise the program cannot express the intended dependency simply by drawing two connecting lines.

The aligned variant also rounds the interpolated point; Alt selects that variant during placement. Compare it with unaligned interpolation at neighboring sizes, because another rounding step can introduce an unnecessary unevenness.

Delta Instructions

A delta moves a point by a fraction of a pixel at specified PPM sizes. The visual workflow uses eighth-pixel increments. This is a rendered-size correction, not a movement of the source outline in font units.

A Middle Delta runs before the final interpolation of untouched points and can influence nearby points through that later pass. A Final Delta runs afterward and corrects the selected point at the end of the process.

Choose the delta tool, select the intended direction and PPM, and drag the target point by the required adjustment. Inspect the instruction's start/end PPM and shift amount in its options or Code view.

The Final Delta editor keeps the correction values beside the PPM range. Check neighboring sizes as well as the displayed interval after changing a delta.

A delta is active inside its PPM range and inactive outside it. FontLab can merge matching adjustments across adjacent or overlapping ranges; check the resulting range instead of creating several overlapping instructions blindly. Waterfall highlights use cyan for sizes with middle deltas and magenta for sizes with final deltas.

Use deltas after refining zones, stems, alignments, and links. They can fix a particular size but create maintenance work if used to compensate for a poor general program.

The design-time Delta filter is a different feature. Both identify coordinates to move and leave others to follow—the transformed/untouched relation from The Delta Filter. The filter changes the design outline, while a TT delta changes a rendered point at specified pixel sizes.

Managing Instructions and the Code Panel

Select an instruction and delete it through its options or Delete/Backspace. The workspace context menu provides removal by instruction type or for the program. The Remove TT hints Action supplies batch and directional X/Y removal for a selection or the font; see Actions.

The Code panel shows FontLab's editable visual program. Canvas instructions and code lines highlight one another, and newly placed instructions appear in the program. Edit a stem reference or delta range there, then use Compile to apply text changes and inspect the result.

The TrueType Hinting panel places a size preview above the visual instruction list, so you can relate a command to the rendered result.

Arrange Code beside or below the preview according to the space available. Use the waterfall’s PPM field and buttons, or the Less/Greater keys in the hinting context, to choose the problem size; then inspect the points in the magnified glyph view.

Space or Grave provides the pixel-preview view while the tool is active. Compare the pixels with the original and hinted outlines, then return to instruction editing. A program that compiles still needs a size-range proof: inspect the changes before, within, and after every corrected interval.