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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 17:25:40 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 17:25:40 +0000 |
commit | cf7da1843c45a4c2df7a749f7886a2d2ba0ee92a (patch) | |
tree | 18dcde1a8d1f5570a77cd0c361de3b490d02c789 /sphinx/util/png.py | |
parent | Initial commit. (diff) | |
download | sphinx-cf7da1843c45a4c2df7a749f7886a2d2ba0ee92a.tar.xz sphinx-cf7da1843c45a4c2df7a749f7886a2d2ba0ee92a.zip |
Adding upstream version 7.2.6.upstream/7.2.6
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'sphinx/util/png.py')
-rw-r--r-- | sphinx/util/png.py | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/sphinx/util/png.py b/sphinx/util/png.py new file mode 100644 index 0000000..6c94219 --- /dev/null +++ b/sphinx/util/png.py @@ -0,0 +1,43 @@ +"""PNG image manipulation helpers.""" + +from __future__ import annotations + +import binascii +import struct + +LEN_IEND = 12 +LEN_DEPTH = 22 + +DEPTH_CHUNK_LEN = struct.pack('!i', 10) +DEPTH_CHUNK_START = b'tEXtDepth\x00' +IEND_CHUNK = b'\x00\x00\x00\x00IEND\xAE\x42\x60\x82' + + +def read_png_depth(filename: str) -> int | None: + """Read the special tEXt chunk indicating the depth from a PNG file.""" + with open(filename, 'rb') as f: + f.seek(- (LEN_IEND + LEN_DEPTH), 2) + depthchunk = f.read(LEN_DEPTH) + if not depthchunk.startswith(DEPTH_CHUNK_LEN + DEPTH_CHUNK_START): + # either not a PNG file or not containing the depth chunk + return None + else: + return struct.unpack('!i', depthchunk[14:18])[0] + + +def write_png_depth(filename: str, depth: int) -> None: + """Write the special tEXt chunk indicating the depth to a PNG file. + + The chunk is placed immediately before the special IEND chunk. + """ + data = struct.pack('!i', depth) + with open(filename, 'r+b') as f: + # seek to the beginning of the IEND chunk + f.seek(-LEN_IEND, 2) + # overwrite it with the depth chunk + f.write(DEPTH_CHUNK_LEN + DEPTH_CHUNK_START + data) + # calculate the checksum over chunk name and data + crc = binascii.crc32(DEPTH_CHUNK_START + data) & 0xffffffff + f.write(struct.pack('!I', crc)) + # replace the IEND chunk + f.write(IEND_CHUNK) |