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59 lines
1.5 KiB
59 lines
1.5 KiB
4 months ago
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"""
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Various round-to-integer helpers.
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"""
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import math
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import functools
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import logging
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log = logging.getLogger(__name__)
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__all__ = [
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"noRound",
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"otRound",
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"maybeRound",
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"roundFunc",
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]
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def noRound(value):
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return value
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def otRound(value):
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"""Round float value to nearest integer towards ``+Infinity``.
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The OpenType spec (in the section on `"normalization" of OpenType Font Variations <https://docs.microsoft.com/en-us/typography/opentype/spec/otvaroverview#coordinate-scales-and-normalization>`_)
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defines the required method for converting floating point values to
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fixed-point. In particular it specifies the following rounding strategy:
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for fractional values of 0.5 and higher, take the next higher integer;
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for other fractional values, truncate.
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This function rounds the floating-point value according to this strategy
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in preparation for conversion to fixed-point.
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Args:
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value (float): The input floating-point value.
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Returns
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float: The rounded value.
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"""
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# See this thread for how we ended up with this implementation:
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# https://github.com/fonttools/fonttools/issues/1248#issuecomment-383198166
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return int(math.floor(value + 0.5))
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def maybeRound(v, tolerance, round=otRound):
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rounded = round(v)
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return rounded if abs(rounded - v) <= tolerance else v
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def roundFunc(tolerance, round=otRound):
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if tolerance < 0:
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raise ValueError("Rounding tolerance must be positive")
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if tolerance == 0:
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return noRound
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if tolerance >= .5:
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return round
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return functools.partial(maybeRound, tolerance=tolerance, round=round)
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