Created
January 12, 2021 20:49
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Monkey patch for python-docx to enable EMF support
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# encoding: utf-8 | |
# This module monkey patches the docx library to add support for Windows Enhanced Metafile images (EMF) | |
# Put in a local folder and "import docx_emf_patch" to enable EMF support. | |
from __future__ import absolute_import, division, print_function | |
import docx | |
from docx.image.exceptions import UnrecognizedImageError | |
from docx.image.constants import MIME_TYPE | |
from docx.image.exceptions import InvalidImageStreamError | |
from docx.image.helpers import BIG_ENDIAN, StreamReader | |
from docx.image.image import BaseImageHeader | |
import struct | |
def _ImageHeaderFactory(stream): | |
""" | |
Return a |BaseImageHeader| subclass instance that knows how to parse the | |
headers of the image in *stream*. | |
""" | |
from docx.image import SIGNATURES | |
def read_64(stream): | |
stream.seek(0) | |
return stream.read(64) | |
header = read_64(stream) | |
for cls, offset, signature_bytes in SIGNATURES: | |
end = offset + len(signature_bytes) | |
found_bytes = header[offset:end] | |
if found_bytes == signature_bytes: | |
return cls.from_stream(stream) | |
raise UnrecognizedImageError | |
class Emf(BaseImageHeader): | |
""" | |
Image header parser for EMF images | |
""" | |
@property | |
def content_type(self): | |
""" | |
MIME content type for this image, unconditionally `image/emf` for | |
EMF images. | |
""" | |
return MIME_TYPE.EMF | |
@property | |
def default_ext(self): | |
""" | |
Default filename extension, always 'emf' for EMF images. | |
""" | |
return 'emf' | |
@classmethod | |
def from_stream(cls, stream,filename=None): | |
""" | |
Return a |Emf| instance having header properties parsed from image in | |
*stream*. | |
""" | |
""" | |
@0 DWORD iType; // fixed | |
@4 DWORD nSize; // var | |
@8 RECTL rclBounds; | |
@24 RECTL rclFrame; // .01 millimeter units L T R B | |
@40 DWORD dSignature; // ENHMETA_SIGNATURE = 0x464D4520 | |
DWORD nVersion; | |
DWORD nBytes; | |
DWORD nRecords; | |
WORD nHandles; | |
WORD sReserved; | |
DWORD nDescription; | |
DWORD offDescription; | |
DWORD nPalEntries; | |
SIZEL szlDevice; | |
SIZEL szlMillimeters; | |
""" | |
stream.seek(0) | |
x = stream.read(40) | |
stream.seek(0) | |
iType,nSize = struct.unpack("ii",x[0:8]) | |
rclBounds = struct.unpack("iiii",x[8:24]) | |
rclFrame = struct.unpack("iiii",x[24:40]) | |
dpi = 300 | |
horz_dpi = dpi | |
vert_dpi = dpi | |
mmwidth = (rclFrame[2]-rclFrame[0])/100.0 | |
mmheight = (rclFrame[3]-rclFrame[1])/100.0 | |
px_width = int(mmwidth*dpi*0.03937008) | |
px_height = int(mmheight*dpi*0.03937008) | |
#1 dot/inch = 0.03937008 pixel/millimeter | |
return cls(px_width,px_height,horz_dpi,vert_dpi) | |
docx.image.Emf = Emf | |
docx.image.constants.MIME_TYPE.EMF = 'image/emf' | |
docx.image.SIGNATURES = tuple(list(docx.image.SIGNATURES) + [(Emf, 40, b' EMF')]) | |
docx.image.image._ImageHeaderFactory = _ImageHeaderFactory |
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