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