254 lines
9.2 KiB
Python
254 lines
9.2 KiB
Python
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from __future__ import annotations
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import re
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from functools import lru_cache
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from itertools import chain, count
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from typing import Dict, Iterable, Iterator, List, Optional, Set, Tuple
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try:
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from lxml import etree
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except ImportError:
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# lxml is required for subsetting SVG, but we prefer to delay the import error
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# until subset_glyphs() is called (i.e. if font to subset has an 'SVG ' table)
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etree = None
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from fontTools import ttLib
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from fontTools.subset.util import _add_method
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from fontTools.ttLib.tables.S_V_G_ import SVGDocument
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__all__ = ["subset_glyphs"]
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GID_RE = re.compile(r"^glyph(\d+)$")
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NAMESPACES = {
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"svg": "http://www.w3.org/2000/svg",
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"xlink": "http://www.w3.org/1999/xlink",
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}
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XLINK_HREF = f'{{{NAMESPACES["xlink"]}}}href'
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# TODO(antrotype): Replace with functools.cache once we are 3.9+
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@lru_cache(maxsize=None)
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def xpath(path):
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# compile XPath upfront, caching result to reuse on multiple elements
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return etree.XPath(path, namespaces=NAMESPACES)
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def group_elements_by_id(tree: etree.Element) -> Dict[str, etree.Element]:
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# select all svg elements with 'id' attribute no matter where they are
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# including the root element itself:
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# https://github.com/fonttools/fonttools/issues/2548
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return {el.attrib["id"]: el for el in xpath("//svg:*[@id]")(tree)}
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def parse_css_declarations(style_attr: str) -> Dict[str, str]:
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# https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/style
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# https://developer.mozilla.org/en-US/docs/Web/CSS/Syntax#css_declarations
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result = {}
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for declaration in style_attr.split(";"):
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if declaration.count(":") == 1:
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property_name, value = declaration.split(":")
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property_name = property_name.strip()
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result[property_name] = value.strip()
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elif declaration.strip():
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raise ValueError(f"Invalid CSS declaration syntax: {declaration}")
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return result
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def iter_referenced_ids(tree: etree.Element) -> Iterator[str]:
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# Yield all the ids that can be reached via references from this element tree.
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# We currently support xlink:href (as used by <use> and gradient templates),
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# and local url(#...) links found in fill or clip-path attributes
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# TODO(anthrotype): Check we aren't missing other supported kinds of reference
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find_svg_elements_with_references = xpath(
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".//svg:*[ "
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"starts-with(@xlink:href, '#') "
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"or starts-with(@fill, 'url(#') "
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"or starts-with(@clip-path, 'url(#') "
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"or contains(@style, ':url(#') "
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"]",
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)
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for el in chain([tree], find_svg_elements_with_references(tree)):
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ref_id = href_local_target(el)
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if ref_id is not None:
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yield ref_id
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attrs = el.attrib
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if "style" in attrs:
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attrs = {**dict(attrs), **parse_css_declarations(el.attrib["style"])}
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for attr in ("fill", "clip-path"):
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if attr in attrs:
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value = attrs[attr]
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if value.startswith("url(#") and value.endswith(")"):
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ref_id = value[5:-1]
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assert ref_id
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yield ref_id
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def closure_element_ids(
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elements: Dict[str, etree.Element], element_ids: Set[str]
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) -> None:
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# Expand the initial subset of element ids to include ids that can be reached
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# via references from the initial set.
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unvisited = element_ids
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while unvisited:
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referenced: Set[str] = set()
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for el_id in unvisited:
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if el_id not in elements:
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# ignore dangling reference; not our job to validate svg
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continue
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referenced.update(iter_referenced_ids(elements[el_id]))
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referenced -= element_ids
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element_ids.update(referenced)
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unvisited = referenced
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def subset_elements(el: etree.Element, retained_ids: Set[str]) -> bool:
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# Keep elements if their id is in the subset, or any of their children's id is.
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# Drop elements whose id is not in the subset, and either have no children,
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# or all their children are being dropped.
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if el.attrib.get("id") in retained_ids:
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# if id is in the set, don't recurse; keep whole subtree
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return True
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# recursively subset all the children; we use a list comprehension instead
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# of a parentheses-less generator expression because we don't want any() to
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# short-circuit, as our function has a side effect of dropping empty elements.
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if any([subset_elements(e, retained_ids) for e in el]):
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return True
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assert len(el) == 0
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parent = el.getparent()
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if parent is not None:
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parent.remove(el)
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return False
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def remap_glyph_ids(
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svg: etree.Element, glyph_index_map: Dict[int, int]
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) -> Dict[str, str]:
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# Given {old_gid: new_gid} map, rename all elements containing id="glyph{gid}"
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# special attributes
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elements = group_elements_by_id(svg)
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id_map = {}
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for el_id, el in elements.items():
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m = GID_RE.match(el_id)
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if not m:
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continue
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old_index = int(m.group(1))
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new_index = glyph_index_map.get(old_index)
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if new_index is not None:
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if old_index == new_index:
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continue
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new_id = f"glyph{new_index}"
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else:
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# If the old index is missing, the element correspond to a glyph that was
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# excluded from the font's subset.
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# We rename it to avoid clashes with the new GIDs or other element ids.
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new_id = f".{el_id}"
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n = count(1)
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while new_id in elements:
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new_id = f"{new_id}.{next(n)}"
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id_map[el_id] = new_id
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el.attrib["id"] = new_id
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return id_map
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def href_local_target(el: etree.Element) -> Optional[str]:
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if XLINK_HREF in el.attrib:
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href = el.attrib[XLINK_HREF]
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if href.startswith("#") and len(href) > 1:
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return href[1:] # drop the leading #
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return None
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def update_glyph_href_links(svg: etree.Element, id_map: Dict[str, str]) -> None:
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# update all xlink:href="#glyph..." attributes to point to the new glyph ids
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for el in xpath(".//svg:*[starts-with(@xlink:href, '#glyph')]")(svg):
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old_id = href_local_target(el)
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assert old_id is not None
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if old_id in id_map:
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new_id = id_map[old_id]
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el.attrib[XLINK_HREF] = f"#{new_id}"
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def ranges(ints: Iterable[int]) -> Iterator[Tuple[int, int]]:
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# Yield sorted, non-overlapping (min, max) ranges of consecutive integers
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sorted_ints = iter(sorted(set(ints)))
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try:
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start = end = next(sorted_ints)
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except StopIteration:
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return
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for v in sorted_ints:
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if v - 1 == end:
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end = v
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else:
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yield (start, end)
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start = end = v
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yield (start, end)
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@_add_method(ttLib.getTableClass("SVG "))
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def subset_glyphs(self, s) -> bool:
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if etree is None:
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raise ImportError("No module named 'lxml', required to subset SVG")
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# glyph names (before subsetting)
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glyph_order: List[str] = s.orig_glyph_order
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# map from glyph names to original glyph indices
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rev_orig_glyph_map: Dict[str, int] = s.reverseOrigGlyphMap
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# map from original to new glyph indices (after subsetting)
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glyph_index_map: Dict[int, int] = s.glyph_index_map
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new_docs: List[SVGDocument] = []
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for doc in self.docList:
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glyphs = {
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glyph_order[i] for i in range(doc.startGlyphID, doc.endGlyphID + 1)
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}.intersection(s.glyphs)
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if not glyphs:
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# no intersection: we can drop the whole record
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continue
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svg = etree.fromstring(
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# encode because fromstring dislikes xml encoding decl if input is str.
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# SVG xml encoding must be utf-8 as per OT spec.
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doc.data.encode("utf-8"),
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parser=etree.XMLParser(
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# Disable libxml2 security restrictions to support very deep trees.
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# Without this we would get an error like this:
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# `lxml.etree.XMLSyntaxError: internal error: Huge input lookup`
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# when parsing big fonts e.g. noto-emoji-picosvg.ttf.
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huge_tree=True,
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# ignore blank text as it's not meaningful in OT-SVG; it also prevents
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# dangling tail text after removing an element when pretty_print=True
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remove_blank_text=True,
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# don't replace entities; we don't expect any in OT-SVG and they may
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# be abused for XXE attacks
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resolve_entities=False,
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),
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)
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elements = group_elements_by_id(svg)
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gids = {rev_orig_glyph_map[g] for g in glyphs}
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element_ids = {f"glyph{i}" for i in gids}
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closure_element_ids(elements, element_ids)
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if not subset_elements(svg, element_ids):
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continue
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if not s.options.retain_gids:
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id_map = remap_glyph_ids(svg, glyph_index_map)
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update_glyph_href_links(svg, id_map)
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new_doc = etree.tostring(svg, pretty_print=s.options.pretty_svg).decode("utf-8")
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new_gids = (glyph_index_map[i] for i in gids)
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for start, end in ranges(new_gids):
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new_docs.append(SVGDocument(new_doc, start, end, doc.compressed))
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self.docList = new_docs
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return bool(self.docList)
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