Source code for pyface.font

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# license included in LICENSE.txt and may be redistributed only under
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""" Toolkit-independent font utilities.

Pyface fonts are intended to be generic, but able to be mapped fairly well
to most backend toolkit font descriptions.  In most cases we can describe
fonts along the common dimensions that are used by CSS, Wx, and Qt.  However
when it comes to actually working with a font, the toolkit needs to take the
description and produce something that is as close as possible to the
specification, but within the constraints of the toolkit, operating system
and available fonts on the machine where this is being executed.

Because of this inherent ambiguity in font specification, this system tries to
be flexible in what it accepts as a font specification, rather than trying to
specify a unique canoncial form.

Font Properties
---------------

The properties that fonts have are:

Font Family
    A list of font family names in order of preference, such as "Helvetica"
    or "Comic Sans".  In the case of a font that has been selected by the
    toolkit this list will have one value which is the actual font family name.

    There are several generic font family names that can be used as fall-backs
    in case all preferred fonts are unavailable.  The allowed values are:

    "default"
        The application's default system font.

    "fantasy"
        A primarily decorative font, but with recognisable characters.

    "decorative"
        A synonym for "fantasy".

    "serif"
        A proportional serif font, such as Times New Roman or Garamond.

    "roman"
        A synonym for "serif".

    "cursive"
        A font which resembles hand-written cursive text, such as Zapf
        Chancery.

    "script"
        A synonym for "cursive".

    "sans-serif"
        A proportional sans-serif font, such as Helvetica or Arial.

    "swiss"
        A synonym for "sans-serif".

    "monospace"
        A fixed-pitch sans-serif font, such as Source Code Pro or Roboto Mono.
        Commonly used for display of code.

    "modern"
        A synonym for "monospace".

    "typewriter"
        A fixed-pitch serif font which resembles typewritten text, such as
        Courier.  Commonly used for display of code.

    "teletype"
        A synonym for "typewriter".

    These special names will be converted into appropriate toolkit flags which
    correspond to these generic font specifications.

Weight
    How thick or dark the font glyphs are.  These can be given as a number
    from 1 (lightest) to 999 (darkest), but are typically specified by a
    multiple of 100 from 100 to 900, with a number of synonyms such as 'light'
    and 'bold' available for those values.

Stretch
    The amount of horizontal compression or expansion to apply to the glyphs.
    These can be given as a percentage between 50% and 200%, or by strings
    such as 'condensed' and 'expanded' that correspond to those values.

Style
    This selects either 'oblique' or 'italic' variants typefaces of the given
    font family.  If neither is wanted, the value is 'normal'.

Size
    The overall size of the glyphs. This can be expressed either as the
    numeric size in points, or as a string such as "small" or "large".

Variants
    A set of additional font style specifiers, such as "small-caps",
    "strikethrough", "underline" or "overline", where supported by the
    underlying toolkit.

Font Specificiation Class
-------------------------

The Pyface Font class is a HasStrictTraits class which specifies a requested
font.  It has methods that convert the Font class to and from a toolkit Font
class.

"""
from traits.api import (
    BaseCFloat, CList, CSet, Enum, HasStrictTraits, Map, Str,
)
from traits.trait_type import NoDefaultSpecified


#: Font weight synonyms.
#: These are alternate convenience names for font weights.
#: The intent is to allow a developer to use a common name (eg. "bold") instead
#: of having to remember the corresponding number (eg. 700).
#: These come from:
#: - the OpenType specification: https://docs.microsoft.com/en-us/typography/opentype/spec/os2#usweightclass
#: - QFont weights: https://doc.qt.io/qt-5/qfont.html#Weight-enum
#: - WxPython font weights: https://wxpython.org/Phoenix/docs/html/wx.FontWeight.enumeration.html
#: - CSS Common weight name mapping: https://developer.mozilla.org/en-US/docs/Web/CSS/font-weight#common_weight_name_mapping
#: - values used by Enable: https://github.com/enthought/enable/blob/78d2e494097fac71cc5c73efef5fb464963fb4db/kiva/fonttools/_constants.py#L90-L105
#: See also: https://gist.github.com/lukaszgrolik/5849599
WEIGHTS = {str(i): i for i in range(100, 1001, 100)}
WEIGHTS.update({
    'thin': 100,
    'hairline': 100,
    'extra-light': 200,
    'ultra-light': 200,
    'ultralight': 200,
    'light': 300,
    'normal': 400,
    'regular': 400,
    'book': 400,
    'medium': 500,
    'roman': 500,
    'semi-bold': 600,
    'demi-bold': 600,
    'demi': 600,
    'bold': 700,
    'extra-bold': 800,
    'ultra-bold': 800,
    'extra bold': 800,
    'black': 900,
    'heavy': 900,
    'extra-heavy': 1000,
})

#: Font stretch synonyms.
#: These are alternate convenience names for font stretch/width values.
#: The intent is to allow a developer to use a common name (eg. "expanded")
#: instead of having to remember the corresponding number (eg. 125).
#: These come from:
#: - the OpenType specification: https://docs.microsoft.com/en-us/typography/opentype/spec/os2#uswidthclass
#: - QFont stetch: https://doc.qt.io/qt-5/qfont.html#Stretch-enum
#: - CSS font-stretch: https://developer.mozilla.org/en-US/docs/Web/CSS/font-stretch
#: - values used by Enable: https://github.com/enthought/enable/blob/78d2e494097fac71cc5c73efef5fb464963fb4db/kiva/fonttools/_constants.py#L78-L88
STRETCHES = {
    'ultra-condensed': 50,
    'extra-condensed': 62.5,
    'condensed': 75,
    'semi-condensed': 87.5,
    'normal': 100,
    'semi-expanded': 112.5,
    'expanded': 125,
    'extra-expanded': 150,
    'ultra-expanded': 200,
}

#: Font size synonyms.
#: These are alternate convenience names for font size values.
#: The intent is to allow a developer to use a common name (eg. "small")
#: instead of having to remember the corresponding number (eg. 10).
#: These come from CSS font-size: https://developer.mozilla.org/en-US/docs/Web/CSS/font-size
SIZES = {
    'xx-small': 7.0,
    'x-small': 9.0,
    'small': 10.0,
    'medium': 12.0,
    'large': 14.0,
    'x-large': 18.0,
    'xx-large': 20.0,
}

STYLES = ('normal', 'italic', 'oblique')

#: Font variants. Currently only small caps variants are exposed in Qt, and
#: nothing in Wx.  In the future this could include things like swashes,
#: numeric variants, and so on, as exposed in the toolkit.
VARIANTS = ['small-caps']

#: Additional markings on or around the glyphs of the font that are not part
#: of the glyphs themselves.  Currently Qt and Wx support underline and
#: strikethrough, and Qt supports overline.  In the future overlines and other
#: decorations may be supported, as exposed in the toolkit.
DECORATIONS = ['underline', 'strikethrough', 'overline']

#: A trait for font families.
FontFamily = CList(Str, ['default'])

#: A trait for font weights.
FontWeight = Map(WEIGHTS, default_value='normal')

#: A trait for font styles.
FontStyle = Enum(STYLES)

#: A trait for font variant properties.
FontVariants = CSet(Enum(VARIANTS))

#: A trait for font decorator properties.
FontDecorations = CSet(Enum(DECORATIONS))


[docs]class FontStretch(BaseCFloat): """ Trait type for font stretches. The is a CFloat trait which holds floating point values between 50 and 200, inclusive. In addition to values which can be converted to floats, this trait also accepts named synonyms for sizes which are converted to the associated commonly accepted weights: - 'ultra-condensed': 50 - 'extra-condensed': 62.5 - 'condensed': 75 - 'semi-condensed': 87.5 - 'normal': 100 - 'semi-expanded': 112.5 - 'expanded': 125 - 'extra-expanded': 150 - 'ultra-expanded': 200 """ #: The default value for the trait. default_value = 100.0 def __init__(self, default_value=NoDefaultSpecified, **metadata): if default_value != NoDefaultSpecified: default_value = self.validate(None, None, default_value) super().__init__(default_value, **metadata)
[docs] def validate(self, object, name, value): if isinstance(value, str) and value.endswith('%'): value = value[:-1] value = STRETCHES.get(value, value) value = super().validate(object, name, value) if not 50 <= value <= 200: self.error(object, name, value) return value
[docs] def info(self): info = ( "a float from 50 to 200, " "a value that can convert to a float from 50 to 200, " ) info += ', '.join(repr(key) for key in SIZES) info += ( " or a string with a float value from 50 to 200 followed by '%'" ) return info
[docs]class FontSize(BaseCFloat): """ Trait type for font sizes. The is a CFloat trait which also allows values which are keys of the size dictionary, and also ignores trailing 'pt' ot 'px' annotation in string values. The value stored is a float. """ #: The default value for the trait. default_value = 12.0 def __init__(self, default_value=NoDefaultSpecified, **metadata): if default_value != NoDefaultSpecified: default_value = self.validate(None, None, default_value) super().__init__(default_value, **metadata)
[docs] def validate(self, object, name, value): if ( isinstance(value, str) and (value.endswith('pt') or value.endswith('px')) ): value = value[:-2] value = SIZES.get(value, value) value = super().validate(object, name, value) if value <= 0: self.error(object, name, value) return value
[docs] def info(self): info = ( "a positive float, a value that can convert to a positive float, " ) info += ', '.join(repr(key) for key in SIZES) info += ( " or a string with a positive float value followed by 'pt' or 'px'" ) return info
[docs]class Font(HasStrictTraits): """A toolkit-independent font specification. This class represents a *request* for a font with certain characteristics, not a concrete font that can be used for drawing. Font objects returned from the toolkit may or may not match what was requested, depending on the capabilities of the toolkit, OS, and the fonts installed on a particular computer. """ #: The preferred font families. family = FontFamily() #: The weight of the font. weight = FontWeight() #: How much the font is expanded or compressed. stretch = FontStretch() #: The style of the font. style = FontStyle() #: The size of the font. size = FontSize() #: The font variants. variants = FontVariants() #: The font decorations. decorations = FontDecorations()
[docs] @classmethod def from_toolkit(cls, toolkit_font): """ Create a Font from a toolkit font object. Parameters ---------- toolkit_font : any A toolkit font to be converted to a corresponding class instance, within the limitations of the options supported by the class. """ from pyface.toolkit import toolkit_object toolkit_font_to_properties = toolkit_object( 'font:toolkit_font_to_properties') return cls(**toolkit_font_to_properties(toolkit_font))
[docs] def to_toolkit(self): """ Create a toolkit font object from the Font instance. Returns ------- toolkit_font : any A toolkit font which matches the property of the font as closely as possible given the constraints of the toolkit. """ from pyface.toolkit import toolkit_object font_to_toolkit_font = toolkit_object('font:font_to_toolkit_font') return font_to_toolkit_font(self)
def __str__(self): """ Produce a CSS2-style representation of the font. """ terms = [] if self.style != 'normal': terms.append(self.style) terms.extend( variant for variant in VARIANTS if variant in self.variants ) terms.extend( decoration for decoration in DECORATIONS if decoration in self.decorations ) if self.weight != 'normal': terms.append(self.weight) if self.stretch != 100: terms.append("{:g}%".format(self.stretch)) size = self.size # if size is an integer we want "12pt" not "12.pt" if int(size) == size: size = int(size) terms.append("{}pt".format(size)) terms.append( ', '.join( repr(family) if ' ' in family else family for family in self.family ) ) return ' '.join(terms) def __repr__(self): traits = self.trait_get(self.editable_traits()) trait_args = ', '.join( "{}={!r}".format(name, value) for name, value in traits.items() ) return "{}({})".format(self.__class__.__name__, trait_args)