removeOverlaps.py

""" Simplify TrueType glyphs by merging overlapping contours/components.

Requires https://github.com/fonttools/skia-pathops
"""

import itertools
import logging
from typing import Callable, Iterable, Optional, Mapping

from fontTools.misc.roundTools import otRound
from fontTools.ttLib import ttFont
from fontTools.ttLib.tables import _g_l_y_f
from fontTools.ttLib.tables import _h_m_t_x
from fontTools.pens.ttGlyphPen import TTGlyphPen

import pathops


__all__ = ["removeOverlaps"]


class RemoveOverlapsError(Exception):
    pass


log = logging.getLogger("fontTools.ttLib.removeOverlaps")

_TTGlyphMapping = Mapping[str, ttFont._TTGlyph]


def skPathFromGlyph(glyphName: str, glyphSet: _TTGlyphMapping) -> pathops.Path:
    path = pathops.Path()
    pathPen = path.getPen(glyphSet=glyphSet)
    glyphSet[glyphName].draw(pathPen)
    return path


def skPathFromGlyphComponent(
    component: _g_l_y_f.GlyphComponent, glyphSet: _TTGlyphMapping
):
    baseGlyphName, transformation = component.getComponentInfo()
    path = skPathFromGlyph(baseGlyphName, glyphSet)
    return path.transform(*transformation)


def componentsOverlap(glyph: _g_l_y_f.Glyph, glyphSet: _TTGlyphMapping) -> bool:
    if not glyph.isComposite():
        raise ValueError("This method only works with TrueType composite glyphs")
    if len(glyph.components) < 2:
        return False  # single component, no overlaps

    component_paths = {}

    def _get_nth_component_path(index: int) -> pathops.Path:
        if index not in component_paths:
            component_paths[index] = skPathFromGlyphComponent(
                glyph.components[index], glyphSet
            )
        return component_paths[index]

    return any(
        pathops.op(
            _get_nth_component_path(i),
            _get_nth_component_path(j),
            pathops.PathOp.INTERSECTION,
            fix_winding=False,
            keep_starting_points=False,
        )
        for i, j in itertools.combinations(range(len(glyph.components)), 2)
    )


def ttfGlyphFromSkPath(path: pathops.Path) -> _g_l_y_f.Glyph:
    # Skia paths have no 'components', no need for glyphSet
    ttPen = TTGlyphPen(glyphSet=None)
    path.draw(ttPen)
    glyph = ttPen.glyph()
    assert not glyph.isComposite()
    # compute glyph.xMin (glyfTable parameter unused for non composites)
    glyph.recalcBounds(glyfTable=None)
    return glyph


def _round_path(
    path: pathops.Path, round: Callable[[float], float] = otRound
) -> pathops.Path:
    rounded_path = pathops.Path()
    for verb, points in path:
        rounded_path.add(verb, *((round(p[0]), round(p[1])) for p in points))
    return rounded_path


def _simplify(path: pathops.Path, debugGlyphName: str) -> pathops.Path:
    # skia-pathops has a bug where it sometimes fails to simplify paths when there
    # are float coordinates and control points are very close to one another.
    # Rounding coordinates to integers works around the bug.
    # Since we are going to round glyf coordinates later on anyway, here it is
    # ok(-ish) to also round before simplify. Better than failing the whole process
    # for the entire font.
    # https://bugs.chromium.org/p/skia/issues/detail?id=11958
    # https://github.com/google/fonts/issues/3365
    # TODO(anthrotype): remove once this Skia bug is fixed
    try:
        return pathops.simplify(path, clockwise=path.clockwise)
    except pathops.PathOpsError:
        pass

    path = _round_path(path)
    try:
        path = pathops.simplify(path, clockwise=path.clockwise)
        log.debug(
            "skia-pathops failed to simplify '%s' with float coordinates, "
            "but succeded using rounded integer coordinates",
            debugGlyphName,
        )
        return path
    except pathops.PathOpsError as e:
        if log.isEnabledFor(logging.DEBUG):
            path.dump()
        raise RemoveOverlapsError(
            f"Failed to remove overlaps from glyph {debugGlyphName!r}"
        ) from e

    raise AssertionError("Unreachable")


def removeTTGlyphOverlaps(
    glyphName: str,
    glyphSet: _TTGlyphMapping,
    glyfTable: _g_l_y_f.table__g_l_y_f,
    hmtxTable: _h_m_t_x.table__h_m_t_x,
    removeHinting: bool = True,
) -> bool:
    glyph = glyfTable[glyphName]
    # decompose composite glyphs only if components overlap each other
    if (
        glyph.numberOfContours > 0
        or glyph.isComposite()
        and componentsOverlap(glyph, glyphSet)
    ):
        path = skPathFromGlyph(glyphName, glyphSet)

        # remove overlaps
        path2 = _simplify(path, glyphName)

        # replace TTGlyph if simplified path is different (ignoring contour order)
        if {tuple(c) for c in path.contours} != {tuple(c) for c in path2.contours}:
            glyfTable[glyphName] = glyph = ttfGlyphFromSkPath(path2)
            # simplified glyph is always unhinted
            assert not glyph.program
            # also ensure hmtx LSB == glyph.xMin so glyph origin is at x=0
            width, lsb = hmtxTable[glyphName]
            if lsb != glyph.xMin:
                hmtxTable[glyphName] = (width, glyph.xMin)
            return True

    if removeHinting:
        glyph.removeHinting()
    return False


def removeOverlaps(
    font: ttFont.TTFont,
    glyphNames: Optional[Iterable[str]] = None,
    removeHinting: bool = True,
    ignoreErrors=False,
) -> None:
    """Simplify glyphs in TTFont by merging overlapping contours.

    Overlapping components are first decomposed to simple contours, then merged.

    Currently this only works with TrueType fonts with 'glyf' table.
    Raises NotImplementedError if 'glyf' table is absent.

    Note that removing overlaps invalidates the hinting. By default we drop hinting
    from all glyphs whether or not overlaps are removed from a given one, as it would
    look weird if only some glyphs are left (un)hinted.

    Args:
        font: input TTFont object, modified in place.
        glyphNames: optional iterable of glyph names (str) to remove overlaps from.
            By default, all glyphs in the font are processed.
        removeHinting (bool): set to False to keep hinting for unmodified glyphs.
        ignoreErrors (bool): set to True to ignore errors while removing overlaps,
            thus keeping the tricky glyphs unchanged (fonttools/fonttools#2363).
    """
    try:
        glyfTable = font["glyf"]
    except KeyError:
        raise NotImplementedError("removeOverlaps currently only works with TTFs")

    hmtxTable = font["hmtx"]
    # wraps the underlying glyf Glyphs, takes care of interfacing with drawing pens
    glyphSet = font.getGlyphSet()

    if glyphNames is None:
        glyphNames = font.getGlyphOrder()

    # process all simple glyphs first, then composites with increasing component depth,
    # so that by the time we test for component intersections the respective base glyphs
    # have already been simplified
    glyphNames = sorted(
        glyphNames,
        key=lambda name: (
            glyfTable[name].getCompositeMaxpValues(glyfTable).maxComponentDepth
            if glyfTable[name].isComposite()
            else 0,
            name,
        ),
    )
    modified = set()
    for glyphName in glyphNames:
        try:
            if removeTTGlyphOverlaps(
                glyphName, glyphSet, glyfTable, hmtxTable, removeHinting
            ):
                modified.add(glyphName)
        except RemoveOverlapsError:
            if not ignoreErrors:
                raise
            log.error("Failed to remove overlaps for '%s'", glyphName)

    log.debug("Removed overlaps for %s glyphs:\n%s", len(modified), " ".join(modified))


def main(args=None):
    import sys

    if args is None:
        args = sys.argv[1:]

    if len(args) < 2:
        print(
            f"usage: fonttools ttLib.removeOverlaps INPUT.ttf OUTPUT.ttf [GLYPHS ...]"
        )
        sys.exit(1)

    src = args[0]
    dst = args[1]
    glyphNames = args[2:] or None

    with ttFont.TTFont(src) as f:
        removeOverlaps(f, glyphNames)
        f.save(dst)


if __name__ == "__main__":
    main()