Custom parameters

With custom parameters, you can set your Font Info more precisely, you can trigger filters at export time, and do other cool stuff, batch-processing a font at export. That way, you can work non-destructively.

Adding and managing custom parameters

You add custom parameters in File > Font Info, in either of the Font, Masters and Exports tabs. To add a parameter, click on the plus button next to the Custom Parameters section of the respective tab, and a dialog containing inline documentation will fly out. The dialog lists names of possible parameters. You can search and scroll through them, and when you click on a name, its description will be displayed on the right:

Confirm your selection of a parameter with a double click or the Return key. A new line will appear, with the name of the parameter and its value:

The left-most checkbox enables the parameter. Turning the checkbox off will make Glyphs act as if it had not been added in the first place. That means that either the setting in question will fallback to its default, or not be written into the font file at all.
To the right of the name is the value. You will usually be able to select and edit it directly in the line. Some parameters will bring up a dialog after you click on the value, such as the Rename Glyphs and TTF Autohint Options parameters:

Select a parameter by clicking on its name. Shift- and Cmd-click to select many parameters at once. You can also copy and paste them between Glyphs files. You can drag to rearrange the parameters. Usually, the order does not matter, but it does for Filter parameters (see below).

Parameters in Font Info > Font count for the whole font, but are overridden by parameters with the same name in the Exports tab.

Almost all parameters in Font Info > Masters are number values, because they get interpolated in a Multiple Master setup. If you use parameters here, make sure they are compatible between the masters. Otherwise, Glyphs will not be able to interpolate. Many vertical metric values can be controlled here. Like font parameters, a master parameter will be overridden by an instance parameter with the same name.

Parameters in the Exports tab directly apply only to the respective font instance that is being exported. Instance parameters override master and font parameters.

Purpose

Custom parameters serve various purposes. Most of them give you the option to set (or help calculate) a value in the final OpenType font, and are applied at export. E.g., glyphOrder influences the ordering of glyphs in the exported font file.

Some parameters only influence the appearance of the font in an Edit tab. For instance, EditView Line Height in Font Info > Font lets you set the line distance for multiline editing in an Edit tab.

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All the custom parameters are documented inside the dialog that adds them. Read carefully through the possible options to make the most of it.

Same but different: properties

Similar to parameters, you will find a section called General at the top of Font Info > Font and Exports. For the most part, they list naming properties, most of which directly influence the OpenType name table in font exports.

Yes there is also a General section in Font Info > Masters, but that one is only for setting the master icon and master name inside the Glyphs UI. They are just there for your viewing and sorting and categorizing pleasure, and have no influence whatsoever on the exported fonts.

The best thing about properties is that you can localize them. Add a localizable property via the plus button in the General section. Then, for each language, add an entry by clicking on the plus button next to the first entry:

If you want to get rid of the first entry, hold down the Opt key and the plus will turn into a minus button.

One of my personal favorites is the optional sample text that can be stored inside an OpenType font. To add one to your font, go into File > Font Info > Font (Cmd-I), add a property by clicking on the plus button in the General section. Pick Sample texts from the dialog that pops up and confirm your entry by pressing the Return or Enter key. As value, you can type in some funny sentence. After you export the font, open it in Font Book, and you are presented with the familiar installation dialog, showing the sample text you just entered:

Take a minute and scrub through the possible general properties. All documentation is presented within the dialog.

Filters

You know how to use the filters from the Filters menu. Sometimes, it is a better idea to not apply them at once, but to put them into a custom parameter and have them executed automatically when the font is exported. The easiest way to get them as a parameter is to open them from the Filters menu, and, instead of applying them to your current glyph selection, open the gear menu in the lower left corner:

Then, click Cancel to get rid of the dialog. (Exactly, do not apply the filter.) Open File > Font Info > Exports (Cmd-I), pick one or more instances, and paste. The filter will show up as a custom parameter:

Yes, you guessed it. You do not always need to copy the custom parameter from the dialog. Rather, you can edit the value directly in the parameter. There are even some functions that can be triggered with a custom parameter but do not even have a dialog with a gear menu. The inline documentation lists AddExtremes and RemoveOverlap.

All built-in and third-party filters accept an additional include: or exclude: parameter at the end of the line, followed by a comma-separated list of glyph names, e.g.:

Transformations; LSB:-20; RSB:+20; include:A,B,C

This example will decrease the left sidebearing by 20, and increase the right sidebearing by the same amount, effectively shifting the glyph to the left. But it will do so only for A, B and C.

Filter vs. PreFilter

Further above, I told you that filters are applied at export. That was not the whole truth, I must admit. To really be precise Filters are applied after decomposition (either in a CFF or overlapping components in a TTF) and overlap removal (if selected in the export dialog). If you want a filter to apply before decomposition and overlap removal, add a PreFilter instead. The values are the same as for the Filter.

Needless to say, both Filter and PreFilter parameters only makes sense in a static font export. They are not available in a variable font because they jeopardize outline compatibility.

Copying and pasting parameters

You can copy and paste parameters between masters, instances, or fonts simply with Cmd-C and Cmd-V. You can paste in multiple masters or multiple instances at once. To do that, just Shift- or Cmd-click on the masters or instances listed in the sidebar on the left, and paste.

You can even paste a parameter into a text editor. You’ll get something like this:

{
    customParameters = (
        {
            name = InterpolationWeightY;
            value = 80;
        },
        {
            name = Filter;
            value = "OffsetCurve;35;35;1;0.5;cap:2;";
        },
        {
            name = "Scale to UPM";
            value = 800;
        }
    );
}

You can see where this is going. If you are handy with your editor and find it tedious to tab through all the parameters in the window, you can quickly batch edit your custom parameters in your editor, or have them calculated by a script etc. In the end, you just copy and paste them back.

Update 2022-08-12: updated title, related articles, minor formatting.