What is Font Gadgets?

This is a package that adds more methods to FontParts and defcon objects using monkey patching. It's one way of adding more high level functions to these packages without having to modify their code directly. Some methods and attributes are already added using this package like glyph.features for finding glyph related substitutions and some other methods to make it easier to change kerning groups. Also you can use font.scale to scale the whole font or font.subset to subset the font to a smaller glyph set.

Usage

Add your own methods to FontParts/Defcon objects by simply defining a function. The first argument of the function should be a name of a defcon object, like font, glyph, etc. Before the function definition, use one of the decorators from this package:

font_method: to add the function as a method to a defcon/fontParts class

font_cached_method: to add the function as a cached method to a defcon/fontParts class. You need to pass destructive notifications to this decorator. See the example below.

font_property: to add the function as a dynamic attribute (property) to a defcon/fontParts class.

font_cached_property: to add the function as a cached dynamic attribute (property) to a defcon/fontParts class. You need to pass destructive notifications to this decorator. See the example below.

When you define a function with one of these decorators, fontgadgets first adds it the defcon package and then also to fontParts. You can explicitly ask fontgadgets to an object using type hints. More details below.

Examples

Adding a dynamic attribute (property)

Define a new dynamic attribute (property) for glyph object:

from fontgadgets.decorators import font_property

@font_property
def isComposite(glyph):
    return len(glyph.contours) == 0 and len(glyph.components) > 0

Please note that the first argument is a glyph. This will tell fontgadgets to register this method for defcon.Glyph and fontParts.fontshell.RGlyph objects.

>>> glyph.isComposite
True

Adding a cached method

You can also define a method that can be more efficient if the code is performance heavy. Make sure the argument types are immutable (e.g. int, str, etc.):

from fontgadgets.decorators import font_cached_method
from drawBot import BezierPath
from defcon import Glyph
from fontTools.pens.cocoaPen import CocoaPen

@font_cached_method("Glyph.ContoursChanged", "Glyph.ComponentsChanged", "Component.BaseGlyphChanged")
def getStroked(glyph, strokeWidth):
    """
    Returns a stroked copy of the glyph with the defined stroked width. The `strokeWidth` is an integer.
    """
    print('One more time!')
    pen = CocoaPen(glyph.font)
    glyph.draw(pen)
    bezierPath = BezierPath(pen.path)
    bezierPath.removeOverlap()
    newPath = bezierPath.expandStroke(strokeWidth).removeOverlap()
    union = newPath.union(bezierPath)
    result = Glyph()
    p = result.getPen()
    union.drawToPen(p)
    return result

g = CurrentGlyph()
g.getStroked(10)

This new method will only be executed if any of the destructive notifications from the font_cached_method have been posted from changes. This makes it faster to fetch the result if you want to call it over and over. In the above example if you run the code in RoboFont, you can see that in the output 'One more time' will be printed only when you run the code first time. The other times the function body is not executed and only the result is returned.

The cached result is kept until there are changes in the glyph object. These changes should be passed to the font_cached_method and they're from defcon package. This way we have more explicit way of observing changes and what causes the cached result to become obsolete.

Choosing which package/object to add the method to

By default the defined functions will be added to defcon and if there is an equivalent object in fontParts, the fontParts object will also get the new methid. But these packages are not same and sometimes there are object in one package that doesn't exist in another. You can ask fontgadgets to add the function to only one package using type hints.

Just pass the target object as the type hint to the first argument:

from fontgadgets.decorators import font_method

@font_method
def myFunction(segment: RSegment):
    # do stuff on an instance of RSegment object
    pass

Return type

Since fontgadgets to by default adds the method to defcon, if there is a return type, it is also a defcon type of object. The problem is when this method is also added to a fontParts object. Then it will also return the defcon object not the fontParts one.

If you want the equivalent fontParts object to return the fontParts object instead of defcon, you need to use type hints on the return type:

from fontgadgets.decorators import font_method

@font_method
def subset(font) -> defcon.Font:
    # subset the font and return a new font
    return font

Here we are hinting fontgadgets that return type is a defcon.Font object. Since there are no type hints for the first font argument, this method will be added first to defcon and then fontParts font object. When fontgadgets registers the function for fontParts.fontshell.RFont object it will make sure the return type of the method will be wrapped in an RFont object to make the method consistent with its package.

Warning

This package is in active development and while being stable enough to add methods to font objects, it is currently in alpha stage. This means that occasionally the public interface will change (for example names of options or functions added to the objects by this package). Please report any problems in the issues section of the repo, I try to fix them as soon as I can.