Source code for fontTools.cu2qu.ufo

# Copyright 2015 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


"""Converts cubic bezier curves to quadratic splines.

Conversion is performed such that the quadratic splines keep the same end-curve
tangents as the original cubics. The approach is iterative, increasing the
number of segments for a spline until the error gets below a bound.

Respective curves from multiple fonts will be converted at once to ensure that
the resulting splines are interpolation-compatible.
"""

import logging
from fontTools.pens.basePen import AbstractPen
from fontTools.pens.pointPen import PointToSegmentPen
from fontTools.pens.reverseContourPen import ReverseContourPen

from . import curves_to_quadratic
from .errors import (
    UnequalZipLengthsError, IncompatibleSegmentNumberError,
    IncompatibleSegmentTypesError, IncompatibleGlyphsError,
    IncompatibleFontsError)


__all__ = ['fonts_to_quadratic', 'font_to_quadratic']

# The default approximation error below is a relative value (1/1000 of the EM square).
# Later on, we convert it to absolute font units by multiplying it by a font's UPEM
# (see fonts_to_quadratic).
DEFAULT_MAX_ERR = 0.001
CURVE_TYPE_LIB_KEY = "com.github.googlei18n.cu2qu.curve_type"

logger = logging.getLogger(__name__)


_zip = zip
def zip(*args):
    """Ensure each argument to zip has the same length. Also make sure a list is
    returned for python 2/3 compatibility.
    """

    if len(set(len(a) for a in args)) != 1:
        raise UnequalZipLengthsError(*args)
    return list(_zip(*args))


class GetSegmentsPen(AbstractPen):
    """Pen to collect segments into lists of points for conversion.

    Curves always include their initial on-curve point, so some points are
    duplicated between segments.
    """

    def __init__(self):
        self._last_pt = None
        self.segments = []

    def _add_segment(self, tag, *args):
        if tag in ['move', 'line', 'qcurve', 'curve']:
            self._last_pt = args[-1]
        self.segments.append((tag, args))

    def moveTo(self, pt):
        self._add_segment('move', pt)

    def lineTo(self, pt):
        self._add_segment('line', pt)

    def qCurveTo(self, *points):
        self._add_segment('qcurve', self._last_pt, *points)

    def curveTo(self, *points):
        self._add_segment('curve', self._last_pt, *points)

    def closePath(self):
        self._add_segment('close')

    def endPath(self):
        self._add_segment('end')

    def addComponent(self, glyphName, transformation):
        pass


def _get_segments(glyph):
    """Get a glyph's segments as extracted by GetSegmentsPen."""

    pen = GetSegmentsPen()
    # glyph.draw(pen)
    # We can't simply draw the glyph with the pen, but we must initialize the
    # PointToSegmentPen explicitly with outputImpliedClosingLine=True.
    # By default PointToSegmentPen does not outputImpliedClosingLine -- unless
    # last and first point on closed contour are duplicated. Because we are
    # converting multiple glyphs at the same time, we want to make sure
    # this function returns the same number of segments, whether or not
    # the last and first point overlap.
    # https://github.com/googlefonts/fontmake/issues/572
    # https://github.com/fonttools/fonttools/pull/1720
    pointPen = PointToSegmentPen(pen, outputImpliedClosingLine=True)
    glyph.drawPoints(pointPen)
    return pen.segments


def _set_segments(glyph, segments, reverse_direction):
    """Draw segments as extracted by GetSegmentsPen back to a glyph."""

    glyph.clearContours()
    pen = glyph.getPen()
    if reverse_direction:
        pen = ReverseContourPen(pen)
    for tag, args in segments:
        if tag == 'move':
            pen.moveTo(*args)
        elif tag == 'line':
            pen.lineTo(*args)
        elif tag == 'curve':
            pen.curveTo(*args[1:])
        elif tag == 'qcurve':
            pen.qCurveTo(*args[1:])
        elif tag == 'close':
            pen.closePath()
        elif tag == 'end':
            pen.endPath()
        else:
            raise AssertionError('Unhandled segment type "%s"' % tag)


def _segments_to_quadratic(segments, max_err, stats):
    """Return quadratic approximations of cubic segments."""

    assert all(s[0] == 'curve' for s in segments), 'Non-cubic given to convert'

    new_points = curves_to_quadratic([s[1] for s in segments], max_err)
    n = len(new_points[0])
    assert all(len(s) == n for s in new_points[1:]), 'Converted incompatibly'

    spline_length = str(n - 2)
    stats[spline_length] = stats.get(spline_length, 0) + 1

    return [('qcurve', p) for p in new_points]


def _glyphs_to_quadratic(glyphs, max_err, reverse_direction, stats):
    """Do the actual conversion of a set of compatible glyphs, after arguments
    have been set up.

    Return True if the glyphs were modified, else return False.
    """

    try:
        segments_by_location = zip(*[_get_segments(g) for g in glyphs])
    except UnequalZipLengthsError:
        raise IncompatibleSegmentNumberError(glyphs)
    if not any(segments_by_location):
        return False

    # always modify input glyphs if reverse_direction is True
    glyphs_modified = reverse_direction

    new_segments_by_location = []
    incompatible = {}
    for i, segments in enumerate(segments_by_location):
        tag = segments[0][0]
        if not all(s[0] == tag for s in segments[1:]):
            incompatible[i] = [s[0] for s in segments]
        elif tag == 'curve':
            segments = _segments_to_quadratic(segments, max_err, stats)
            glyphs_modified = True
        new_segments_by_location.append(segments)

    if glyphs_modified:
        new_segments_by_glyph = zip(*new_segments_by_location)
        for glyph, new_segments in zip(glyphs, new_segments_by_glyph):
            _set_segments(glyph, new_segments, reverse_direction)

    if incompatible:
        raise IncompatibleSegmentTypesError(glyphs, segments=incompatible)
    return glyphs_modified


def glyphs_to_quadratic(
        glyphs, max_err=None, reverse_direction=False, stats=None):
    """Convert the curves of a set of compatible of glyphs to quadratic.

    All curves will be converted to quadratic at once, ensuring interpolation
    compatibility. If this is not required, calling glyphs_to_quadratic with one
    glyph at a time may yield slightly more optimized results.

    Return True if glyphs were modified, else return False.

    Raises IncompatibleGlyphsError if glyphs have non-interpolatable outlines.
    """
    if stats is None:
        stats = {}

    if not max_err:
        # assume 1000 is the default UPEM
        max_err = DEFAULT_MAX_ERR * 1000

    if isinstance(max_err, (list, tuple)):
        max_errors = max_err
    else:
        max_errors = [max_err] * len(glyphs)
    assert len(max_errors) == len(glyphs)

    return _glyphs_to_quadratic(glyphs, max_errors, reverse_direction, stats)


[docs]def fonts_to_quadratic( fonts, max_err_em=None, max_err=None, reverse_direction=False, stats=None, dump_stats=False, remember_curve_type=True): """Convert the curves of a collection of fonts to quadratic. All curves will be converted to quadratic at once, ensuring interpolation compatibility. If this is not required, calling fonts_to_quadratic with one font at a time may yield slightly more optimized results. Return True if fonts were modified, else return False. By default, cu2qu stores the curve type in the fonts' lib, under a private key "com.github.googlei18n.cu2qu.curve_type", and will not try to convert them again if the curve type is already set to "quadratic". Setting 'remember_curve_type' to False disables this optimization. Raises IncompatibleFontsError if same-named glyphs from different fonts have non-interpolatable outlines. """ if remember_curve_type: curve_types = {f.lib.get(CURVE_TYPE_LIB_KEY, "cubic") for f in fonts} if len(curve_types) == 1: curve_type = next(iter(curve_types)) if curve_type == "quadratic": logger.info("Curves already converted to quadratic") return False elif curve_type == "cubic": pass # keep converting else: raise NotImplementedError(curve_type) elif len(curve_types) > 1: # going to crash later if they do differ logger.warning("fonts may contain different curve types") if stats is None: stats = {} if max_err_em and max_err: raise TypeError('Only one of max_err and max_err_em can be specified.') if not (max_err_em or max_err): max_err_em = DEFAULT_MAX_ERR if isinstance(max_err, (list, tuple)): assert len(max_err) == len(fonts) max_errors = max_err elif max_err: max_errors = [max_err] * len(fonts) if isinstance(max_err_em, (list, tuple)): assert len(fonts) == len(max_err_em) max_errors = [f.info.unitsPerEm * e for f, e in zip(fonts, max_err_em)] elif max_err_em: max_errors = [f.info.unitsPerEm * max_err_em for f in fonts] modified = False glyph_errors = {} for name in set().union(*(f.keys() for f in fonts)): glyphs = [] cur_max_errors = [] for font, error in zip(fonts, max_errors): if name in font: glyphs.append(font[name]) cur_max_errors.append(error) try: modified |= _glyphs_to_quadratic( glyphs, cur_max_errors, reverse_direction, stats) except IncompatibleGlyphsError as exc: logger.error(exc) glyph_errors[name] = exc if glyph_errors: raise IncompatibleFontsError(glyph_errors) if modified and dump_stats: spline_lengths = sorted(stats.keys()) logger.info('New spline lengths: %s' % (', '.join( '%s: %d' % (l, stats[l]) for l in spline_lengths))) if remember_curve_type: for font in fonts: curve_type = font.lib.get(CURVE_TYPE_LIB_KEY, "cubic") if curve_type != "quadratic": font.lib[CURVE_TYPE_LIB_KEY] = "quadratic" modified = True return modified
def glyph_to_quadratic(glyph, **kwargs): """Convenience wrapper around glyphs_to_quadratic, for just one glyph. Return True if the glyph was modified, else return False. """ return glyphs_to_quadratic([glyph], **kwargs)
[docs]def font_to_quadratic(font, **kwargs): """Convenience wrapper around fonts_to_quadratic, for just one font. Return True if the font was modified, else return False. """ return fonts_to_quadratic([font], **kwargs)