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Improve behaviour of numerial precision reduction

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* Previously all calculations were immediately done with the precision specified by the user, resulting in accumulation of numerical errors and in some cases very discernible abberations from the initial image (e.g. #80)
* Now all calculations are done with default precision (the module "decimal" uses a whopping 28 signifigant digits initially!) and only at the very end coordinates are rounded to the desired precision.
This commit is contained in:
Eduard Braun 2016-08-31 00:04:19 +02:00
parent 3929426a5a
commit 9e4b9d6f5e
1 changed files with 11 additions and 8 deletions
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19
scour/scour.py
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@ -64,12 +64,7 @@ import optparse
from scour.yocto_css import parseCssString from scour.yocto_css import parseCssString
import six import six
from six.moves import range from six.moves import range
from decimal import Context, Decimal, InvalidOperation, getcontext
# Python 2.3- did not have Decimal
try:
from decimal import Decimal, InvalidOperation, getcontext
except ImportError:
sys.stderr.write("Scour requires at least Python 2.7 or Python 3.3+.")
# select the most precise walltime measurement function available on the platform # select the most precise walltime measurement function available on the platform
if sys.platform.startswith('win'): if sys.platform.startswith('win'):
@ -2474,9 +2469,13 @@ def scourUnitlessLength(length, needsRendererWorkaround=False): # length is of a
This is faster than scourLength on elements guaranteed not to This is faster than scourLength on elements guaranteed not to
contain units. contain units.
""" """
# reduce to the proper number of digits
if not isinstance(length, Decimal): if not isinstance(length, Decimal):
length = getcontext().create_decimal(str(length)) length = getcontext().create_decimal(str(length))
# reduce numeric precision
# plus() corresponds to the unary prefix plus operator and applies context precision and rounding
length = scouringContext.plus(length)
# if the value is an integer, it may still have .0[...] attached to it for some reason # if the value is an integer, it may still have .0[...] attached to it for some reason
# remove those # remove those
if int(length) == length: if int(length) == length:
@ -3068,7 +3067,11 @@ def scourString(in_string, options=None):
# sanitize options (take missing attributes from defaults, discard unknown attributes) # sanitize options (take missing attributes from defaults, discard unknown attributes)
options = sanitizeOptions(options) options = sanitizeOptions(options)
getcontext().prec = options.digits # create decimal context with reduced precision for scouring numbers
# calculations should be done in the default context (precision defaults to 28 significant digits) to minimize errors
global scouringContext
scouringContext = Context(prec = options.digits)
global numAttrsRemoved global numAttrsRemoved
global numStylePropsFixed global numStylePropsFixed
global numElemsRemoved global numElemsRemoved