108 lines
4.3 KiB
Python
108 lines
4.3 KiB
Python
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# Copyright 2015 Google, Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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#
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# Google Author(s): Doug Felt
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import svg_cleaner
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class SvgBuilder(object):
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"""Modifies a font to add SVG glyphs from a document or string. Once built you
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can call add_from_filename or add_from_doc multiple times to add SVG
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documents, which should contain a single root svg element representing the glyph.
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This element must have width and height attributes (in px), these are used to
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determine how to scale the glyph. The svg should be designed to fit inside
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this bounds and have its origin at the top left. Adding the svg generates a
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transform to scale and position the glyph, so the svg element should not have
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a transform attribute since it will be overwritten. Any id attribute on the
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glyph is also overwritten.
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Adding a glyph can generate additional default glyphs for components of a
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ligature that are not already present.
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It is possible to add SVG images to a font that already has corresponding
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glyphs. If a glyph exists already, then its hmtx advance is assumed valid.
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Otherwise we will generate an advance based on the image's width and scale
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factor. Callers should ensure that glyphs for components of ligatures are
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added before the ligatures themselves, otherwise glyphs generated for missing
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ligature components will be assigned zero metrics metrics that will not be
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overridden later."""
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def __init__(self, font_builder):
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font_builder.init_svg()
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self.font_builder = font_builder
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self.cleaner = svg_cleaner.SvgCleaner()
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font = font_builder.font
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self.font_ascent = font['hhea'].ascent
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self.font_height = self.font_ascent - font['hhea'].descent
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self.font_upem = font['head'].unitsPerEm
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def add_from_filename(self, ustr, filename):
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with open(filename, "r") as fp:
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return self.add_from_doc(ustr, fp.read())
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def _get_int_px(self, val):
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if not val.lower().endswith('px'):
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raise "expected width or height ending in 'px' but got: %s" % val
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return int(val[:-2])
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def add_from_doc(self, ustr, svgdoc):
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"""Cleans the svg doc, tweaks the root svg element's
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attributes, then updates the font. ustr is the character or ligature
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string, svgdoc is the svg document xml. The doc must have a single
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svg root element."""
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# The svg element must have an id attribute of the form 'glyphNNN' where NNN
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# is the glyph id. We capture the index of the glyph we're adding and write
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# it into the svg.
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#
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# We generate a transform that places the origin at the top left of the
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# ascent and uniformly scales it to fit both the font height (ascent -
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# descent) and glyph advance if it is already present. The width and height
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# attributes are not used by rendering, so they are removed from the element
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# once we're done with them.
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cleaner = self.cleaner
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fbuilder = self.font_builder
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tree = cleaner.tree_from_text(svgdoc)
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cleaner.clean_tree(tree)
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name, index, exists = fbuilder.add_components_and_ligature(ustr)
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tree.attrs['id'] = 'glyph%s' % index
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image_width = self._get_int_px(tree.attrs.pop('width'))
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image_height = self._get_int_px(tree.attrs.pop('height'))
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scale = float(self.font_height) / image_height;
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if exists:
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width = fbuilder.hmtx[name][0]
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# Special case for preexisting zero advance, we scale to height.
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if width > 0:
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hscale = float(width) / image_width;
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if hscale < scale:
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scale = hscale
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transform = 'translate(0, -%s) scale(%s)' % (self.font_ascent, scale)
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tree.attrs['transform'] = transform
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svgdoc = cleaner.tree_to_text(tree)
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hmetrics = None
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if not exists:
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# horiz advance and lsb
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hmetrics = [int(round(image_width * scale)), 0]
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fbuilder.add_svg(svgdoc, hmetrics, name, index)
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