xref: /aosp_15_r20/external/fonttools/Lib/fontTools/cu2qu/ufo.py (revision e1fe3e4ad2793916b15cccdc4a7da52a7e1dd0e9)

# 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, all_quadratic=True):
    """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, all_quadratic)
    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

    if all_quadratic or n == 3:
        return [("qcurve", p) for p in new_points]
    else:
        return [("curve", p) for p in new_points]


def _glyphs_to_quadratic(glyphs, max_err, reverse_direction, stats, all_quadratic=True):
    """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":
            new_segments = _segments_to_quadratic(
                segments, max_err, stats, all_quadratic
            )
            if all_quadratic or new_segments != segments:
                glyphs_modified = True
            segments = new_segments
        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, all_quadratic=True
):
    """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, all_quadratic
    )


def fonts_to_quadratic(
    fonts,
    max_err_em=None,
    max_err=None,
    reverse_direction=False,
    stats=None,
    dump_stats=False,
    remember_curve_type=True,
    all_quadratic=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 in ("quadratic", "mixed"):
                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, all_quadratic
            )
        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")
            new_curve_type = "quadratic" if all_quadratic else "mixed"
            if curve_type != new_curve_type:
                font.lib[CURVE_TYPE_LIB_KEY] = new_curve_type
                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)


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)