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# Copyright 2018 The pybadge Authors
#
# 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
#
# https://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.
"""Measure the width, in pixels, of a string rendered using DejaVu Sans 110pt.
Uses a precalculated set of metrics to calculate the string length.
"""
import io
import json
import pkg_resources
from typing import cast, Mapping, TextIO, Type
from pybadges import text_measurer
class PrecalculatedTextMeasurer(text_measurer.TextMeasurer):
"""Measures the width of a string using a precalculated set of tables."""
_default_cache = None
def __init__(self, default_character_width: float,
char_to_width: Mapping[str, float],
pair_to_kern: Mapping[str, float]):
"""Initializer for PrecalculatedTextMeasurer.
Args:
default_character_width: the average width, in pixels, of a
character in DejaVu Sans 110pt.
char_to_width: a mapping between a character and it's width,
in pixels, in DejaVu Sans 110pt.
pair_to_kern: a mapping between pairs of characters and the kerning
distance between them e.g. text_width("IJ") =>
(char_to_width["I"] + char_to_width["J"]
- pair_to_kern.get("IJ", 0))
"""
self._default_character_width = default_character_width
self._char_to_width = char_to_width
self._pair_to_kern = pair_to_kern
def text_width(self, text: str) -> float:
"""Returns the width, in pixels, of a string in DejaVu Sans 110pt."""
width = 0
for index, c in enumerate(text):
width += self._char_to_width.get(c, self._default_character_width)
width -= self._pair_to_kern.get(text[index:index + 2], 0)
return width
@staticmethod
def from_json(f: TextIO) -> 'PrecalculatedTextMeasurer':
"""Return a PrecalculatedTextMeasurer given a JSON stream.
See precalculate_text.py for details on the required format.
"""
o = json.load(f)
return PrecalculatedTextMeasurer(o['mean-character-length'],
o['character-lengths'],
o['kerning-pairs'])
@classmethod
def default(cls) -> 'PrecalculatedTextMeasurer':
"""Returns a reasonable default PrecalculatedTextMeasurer."""
if cls._default_cache is not None:
return cls._default_cache
if pkg_resources.resource_exists(__name__, 'default-widths.json.xz'):
import lzma
with pkg_resources.resource_stream(__name__,
'default-widths.json.xz') as f:
with lzma.open(f, "rt") as g:
cls._default_cache = PrecalculatedTextMeasurer.from_json(
cast(TextIO, g))
return cls._default_cache
elif pkg_resources.resource_exists(__name__, 'default-widths.json'):
with pkg_resources.resource_stream(__name__,
'default-widths.json') as f:
cls._default_cache = PrecalculatedTextMeasurer.from_json(
io.TextIOWrapper(f, encoding='utf-8'))
return cls._default_cache
else:
raise ValueError('could not load default-widths.json')
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