TrueType Hinting tool»

The TrueType Hinting tool (++Cmd-Shift-F7++) is used to create and modify visual TrueType hints and preview the resulting TrueType contours using the real TrueType rasterizer.

To activate the TrueType Hinting tool, select the “TrueTthype Hinting” command from the Tools menu or click on the
button in the Toolbar.

When the TT Hinting tool becomes active you will see that the editing field of the Glyph window has changed. It enters the TrueType Hinting mode:

Once you are in the TrueType Hinting mode, the Property bar changes, and the Waterfall Preview and TrueType Hinting panel appear.

Hinting Property Bar»

The Glyph window Property bar is the main control center of the TrueType Hinting tool. It allows you to see various information layers in the Glyph window and to control all hinting parameters:

Button Description
Use the PPM controls to select one of the predefined values or enter your own value in the edit field. This allows you to see how outlines are rasterized at different sizes.
Opens the TrueType stems dialog box
Opens the TrueType alignment zones dialog box
Other hinting options including text preview sizes and text strings
Switches the pixel preview between black/white and ClearType - the real Windows system rasterizer.
Shows gridlines. Gridlines mark the edges of pixels that will appear in the selected PPM size
Shows centers of pixels. When the outline is filled, all pixels whose centers are on the outline or inside the outline are set black. This layer is very useful for delta hinting
Shows resulting pixel preview. FontLab uses the real TrueType rasterizer to preview a filled glyph at the selected PPM after interpretation of the instruction program
Shows hinted outline. The original, untouched outline of the glyph always appears in the Glyph window in black. The hinted outline, which is the result of the interpretation of the instruction program, appears in blue
Shows off-curve control points
Automatically hints the glyph and builds the instruction program
Local menu with additional useful hinting commands

Waterfall Preview»

The waterfall preview at the top of the glyph shows how it will look when hinting instructions are applied:

Unhinted “B” Hinted “B”

To select a size as PPM, double-click on that size in the waterfall preview. You can also do this by using the PPM controls in the Property bar.

To change the zoom or completely hide the waterfall preview, use the Waterfall Preview submenu in the local menu :

TrueType Hinting Panel»

The TrueType Hinting panel automatically opens every time you select the TrueType Hinting tool. If you close the panel, switch to another tool, and select the TrueType Hinting tool again, the panel will reappear. The panel contains a local toolbar with main hinting tools on top, a waterfall preview of the current character in context on the left, and the code panel with hinting instructions on the right.


With the TrueType Hinting toolbar you can select the hinting direction, the current visual instruction tool, open the code panel, and compile the instructions in it.

The buttons in the local toolbar are for the following operations:

Button Description
Set vertical direction. Sets visual instruction tools to work in the vertical direction. I.e. create vertical links, alignment, interpolation and deltas. Instructions in different directions are independent of each other
Set horizontal direction
Select the edit tool (E key)
Select Align command (A key)
Select Single Link command (S key)
Select Double Link command (D key)
Select Interpolate command (I key)
Select Middle Delta command (M key)
Select Final Delta command (F key)
Open the Code panel
Compile instructions in the Code panel


If you enter any characters in the edit field under preview, you will see these characters appear in the preview window. Use the usual FontLab rules to enter special characters (enter the character name after a slash “/” character or two slashes to enter a slash: “//”).

With the waterfall preview you can quickly select the current PPM. Just double-click on the sample PPM you want to select.

Code panel»

To open the code panel, click on . It contains the code for visual TrueType hinting instructions. You can manually edit the code here and apply changes by clicking on the button.

Alignment Instructions»

Alignment instructions are used to align points to the grid. There are two types of alignment instructions: those linked with alignment zones and those not linked with zones.

Alignment Zones»

Alignment zones define important vertical positions that are common to many font characters. A good example of an alignment zone is a baseline and the bottom position of the ‘O’ character:

Bottom alignment zone

At low PPM sizes you must set the bottom point of the characters ‘O’, ‘C’ and similar characters to the baseline to suppress the bottom overshoot. In this case we have a so-called bottom alignment zone.

Another example of an alignment zone is the top line of the ‘H’ character and the ‘O’ character:

Top alignment zone

Alignment zones are previewed in the Glyph window with a green and blue colors.

Editing TrueType Alignment Zones»

To add new TrueType zones or edit existing zones, click on the Zones button on the local toolbar.

You will see the Alignment Zones dialog:

The dialog contains a toolbar, two lists of zones and a pair of buttons: Apply and Cancel. The left list stores all information about the top zones (where alignment happens in top-to-bottom direction) and the right list – about the bottom zones.

For each zone you may specify its name, position of the “snap to” line, the zone width and the tag.

To change settings for a zone, simply double-click on the value in the list.

There is a toolbar above zones lists. Use it to call following commands:

Button Description
Add new top or bottom zone, respectively
Remove selected top or bottom zone
Automatically build zones
Reset zones

AlignTop and AlignBottom Instructions»

These instructions are available only when the vertical hinting direction is selected.

To add AlignTop or AlignBottom commands:

  1. Select the Align tool .
  2. Position the cursor over the point that you want to align and click the mouse button.
  3. If the selected point was in one of the alignment zones, an AlignTop or AlignBottom command will be added to the hinting program. If the selected point is not in the zone, the “free” Align command will be added.

The AlignTop command appears as:

The AlignBottom command is similar to the AlignTop command.

How AlignTop and AlignBottom Commands Work

  1. In the prep program (this program interprets every time the PPM is changed) all alignment zones (stored in the cvt table) are aligned to the closest integer position.
  2. When the glyph program interprets, the position of the point aligned to the zone by the AlignTop or AlignBottom command is set equal to the aligned position of the zone if the scaled distance between it and the zone is no more than 16/17 pixels.

The AlignTop and AlignBottom commands have two arguments: the name of the point that is aligned by the command and the name of the zone. In the Code panel these commands appear as:

alignt at01 "T: 1447"
alignb ab01 "B: 0"

where at01 and ab01 are point names and “T: 1447“ and ”B: 0” are names of the top and bottom zones, respectively.

Hinting Alignment Zones»

By default the position of the alignment zones is scaled linearly. Sometimes this may not be satisfactory and you may need to exactly specify the position of the alignment zones at some PPMs.

With FontLab VI you can adjust the position of the zones around the linearly scaled position.

Every alignment zone has a blue or green icon at the left:

You can drag this icon up or down to adjust the position of the zone at the current PPM:

If you move the icon you will see all glyphs that have align commands applied to that zone changed their shape.
You may find this feature useful when you have to add glyphs to an already hinted TrueType font. New glyphs often have a different height at some PPMs and you can correct that with the zone alignment command and zone hinting.

Align Instruction»

Use the Align command when it’s not necessary (or possible – you can’t align points to horizontal alignment zones) to align a point to an alignment zone but you want to align the point’s position to the grid. The Align command is available in both directions.

The Align command allows you to directly control how point coordinates are rounded.

To set an alignment command on the outline:

  1. Select the Align tool .
  2. Position the mouse cursor on the point that you want to align.
  3. Click the mouse button. Hold the Shift key if you are setting vertical commands and the point is inside an alignment zone.

In the Code panel the Align command appears as:

alignv av01 round
alignh ah02 round

where av01 and ah02 are point names and round is the code of the alignment rounding method as shown in the table below.

To select a rounding method, click on the Align instruction (blue circle with anchor) and the Options panel will appear:

Select the align destination and close the panel to apply changes. You will see the code of the alignment rounding method will change in the Code panel.

Here is a graphical description of the various rounding methods:

Rounding Code Description
round Aligns to the closest grid line
left Aligns to the left or bottom grid line
right Aligns to the right or top grid line
center Aligns to the closest center of pixel
double Aligns to closest edge of pixel or center of pixel

Align commands are the very first commands in any hinting program. They do not have base points and affect only one point.


Most of the time, the align and linking commands are enough to hint most characters, but in some cases a very different kind of command is necessary. Look at the enlarged middle-right region of the character B in the vertical direction:

You can see that point iv02 in the original outline in the vertical direction is set exactly between points iv01 and iv03. But because these points are aligned and point iv02 is not controlled it becomes too close to point iv03.

In this and similar cases you can use the interpolate command. This command sets the position of a point in the same proportion between two other points as it was in the original outline.

Or the intermediate point could be aligned to he grid and serve as the starting point for a single link or another interpolation command.

This command has two base points (iv01 and iv03 in our sample) and one affected point (iv02).

To set the interpolate command:

  1. Select the interpolate tool .
  2. Click on the first base point.
  3. Click on the point to interpolate.
  4. Click on the second base point.

Hold down the Alt key if you want to create the aligned interpolate command.

In the Glyph window the interpolate command appears as two green directed lines from the interpolated point to base points.

In the Code panel the interpolate command appears as:

interpolatev iv02 iv01, iv03 

where iv02 is the interpolated point and iv01 and iv03 are the base points.

To delete the command, click on the green interpolation line and then click on Delete in the Options panel.

The Align Destination option is the same that you can see in the Align command’s Options panel and allows to align the destination point to the grid.

Delta Instructions»

Now you know all about the visual hinting commands that can be applied to an outline at all PPMs. In addition to these commands the TrueType hinting language lets you set special commands that will work only at specific PPM sizes. These commands are called delta instructions.

There are two delta instructions for each hinting direction: middle delta instructions and final delta instructions.

Middle Delta Instructions»

A middle delta instruction can move outline points like any other instruction. It can move any outline point in ⅛-pixel increments from one pixel left (or bottom) to one pixel right (or top):

Movement space of delta instruction

Middle delta instructions are interpreted like other commands in the hinting program. They are automatically inserted between “normal” instructions that move points and so can be used to modify the normal interpretation of the hinting program:

In the example above, the vertical stem is moved one pixel to the left when the middle delta instruction is applied.

A middle delta instruction may be applied to a touched or untouched point and the point becomes touched afterwards.

It’s a good idea to use middle delta instructions to correct the rounding direction on some PPMs, like on the character ‘e’ at small PPM sizes.

Another good application of middle delta instructions is the correction of diagonal hints. A middle delta instruction “touches” the point to which it is applied, so any other point between two delta instructions will be interpolated in the final interpolation routine.

To set a middle delta instruction:

  1. Select the Middle Delta tool .
  2. Move the cursor to the point at which you want to set the delta instruction, press the left mouse button and drag to the needed direction.

The middle delta instruction has 4 arguments: point to move, PPM0, PPM1 (the PPM range in which this instruction works), and the shift distance in eighths of pixels. In the Code panel this instruction looks like:

mdeltav mv01 18-20 -6

where mv01 is the point name, 18–20 is the PPM range, -6 is the distance to move (in this case – move down by ¾ of a pixel). This means that point mv01 will be moved down ¾ of a pixel when PPM is 18, 19 or 20.

By default the PPM range is equal to the current PPM. You can edit the middle delta instruction right in the code or in its Options panel:

Active and Inactive Delta Instructions»

Delta instructions may be active or inactive. When the current PPM is within the PPM range of the delta instruction the instruction is active. Otherwise it is inactive.

Active delta instruction (shift down)
Inactive delta instruction


If you set a new middle delta instruction at a point where a delta instruction is already set and is active the old instruction will be replaced by the new one. If you set delta instructions for the same point and with the same shift distance but for different PPM ranges FontLab will try to combine PPM ranges and unite delta instructions where it is possible.

Final Delta Instructions»

Final delta instructions are applied after the final interpolation of all untouched points. They are used as a last resort to shift points to remove or add pixels at PPM sizes where it is still necessary after application of zones, stems and all other hints:

Hinted character at 12 PPM without delta instructions Same character with delta instruction

The sequence of interpretation is the only difference between middle and final delta instructions. They work exactly the same way. To set final delta instructions, select the final delta tool and follow the same instructions as above for middle deltas.

Some recommendations:

  1. Delta hinting is a very time-consuming operation because you have to check the rendering results at many PPMs. So always try first to get the best possible results from normal, linear hinting.
  2. Use the waterfall preview in the TrueType Hinting panel to see where delta hinting is necessary.
  3. Try to set as few delta instructions as possible. They increase font size and complexity.
  4. It’s better to set one delta instruction with a larger range than two less comprehensive delta instructions.

Removing Instructions»

You can remove hinting instructions using three methods:

  1. Select the instruction in the Code panel and press the Del key.
  2. Click on the instruction and then on Delete in the instruction’s Options panel.
  3. Right-click in the Glyph window when the TTH tool is active and choose one of the commands in the context pop-up menu: