def getc():
c = infile.read(1)
if not c:
if not allow_eof or EOF[0]:
raise png.Error('premature End of file')
else:
# small hack to simulate trailing whitespace at the end of file
EOF[0] = True # but only once
return ' '
return c
def deblock(f):
"""
Decompress a single block from a compressed Plan 9 image file.
Each block starts with 2 decimal strings of 12 bytes each. Yields a
sequence of (row, data) pairs where row is the total number of rows
processed according to the file format and data is the decompressed
data for a set of rows.
"""
row = int(f.read(12))
size = int(f.read(12))
if not (0 <= size <= 6000):
raise 'block has invalid size; not a Plan 9 image file?'
# Since each block is at most 6000 bytes we may as well read it all in
# one go.
d = f.read(size)
i = 0
o = []
while i < size:
x = ord(d[i:i + 1]) # hack to avoid interpreting bytes item as int
i += 1
if x & 0x80:
x = (x & 0x7f) + 1
lit = d[i:i + x]
i += x
o.extend(lit)
continue
# x's high-order bit is 0
l = (x >> 2) + 3
# Offset is made from bottom 2 bits of x and all 8 bits of next
# byte. http://plan9.bell-labs.com/magic/man2html/6/image doesn't
# say whether x's 2 bits are most significant or least significant.
# But it is clear from inspecting a random file,
# http://plan9.bell-labs.com/sources/plan9/sys/games/lib/sokoban/images/cargo.bit
# that x's 2 bit are most significant.
offset = (x & 3) << 8
offset |= ord(d[i:i + 1])
i += 1
# Note: complement operator neatly maps (0 to 1023) to (-1 to
# -1024). Adding len(o) gives a (non-negative) offset into o from
# which to start indexing.
offset = ~offset + len(o)
if offset < 0:
raise png.Error('byte offset indexes off the begininning'
'of the output buffer; not a Plan 9 image file?')
for j in range(l):
o.append(o[offset + j])
try:
res = ''.join(o)
except:
res = bytearray(o)
return row, res
def read_pam_header(infile):
"""
Read (the rest of a) PAM header.
`infile` should be positioned
immediately after the initial 'P7' line (at the beginning of the
second line). Returns are as for `read_pnm_header`.
"""
# Unlike PBM, PGM, and PPM, we can read the header a line at a time.
header = dict()
while True:
l = infile.readline().strip()
if l == png.strtobytes('ENDHDR'):
break
if not l:
raise EOFError('PAM ended prematurely')
if l[0] == png.strtobytes('#'):
continue
l = l.split(None, 1)
if l[0] not in header:
header[l[0]] = l[1]
else:
header[l[0]] += png.strtobytes(' ') + l[1]
required = ['WIDTH', 'HEIGHT', 'DEPTH', 'MAXVAL']
required = [png.strtobytes(x) for x in required]
WIDTH, HEIGHT, DEPTH, MAXVAL = required
present = [x for x in required if x in header]
if len(present) != len(required):
raise png.Error('PAM file must specify '
'WIDTH, HEIGHT, DEPTH, and MAXVAL')
width = int(header[WIDTH])
height = int(header[HEIGHT])
depth = int(header[DEPTH])
maxval = int(header[MAXVAL])
if (width <= 0 or height <= 0 or depth <= 0 or maxval <= 0):
raise png.Error(
'WIDTH, HEIGHT, DEPTH, MAXVAL must all be positive integers')
return 'P7', width, height, depth, maxval
def read_int_tokens(infile, n, allow_eof=False):
"""
Read ASCII integers separated with whitespaces as list of length `n`
Skip comments started with '#' to the end of line
If comment starts right after digit and newline starts with digit
these digits form single number.
"""
result = []
EOF = [False] # Hack to allow modification in nested function
# We may consume less or more than one line, so characters read one by one
def getc():
c = infile.read(1)
if not c:
if not allow_eof or EOF[0]:
raise png.Error('premature End of file')
else:
# small hack to simulate trailing whitespace at the end of file
EOF[0] = True # but only once
return ' '
return c
token = bytes()
while True:
c = getc()
if c.isspace():
if token:
# post-token whitespace, save token
result.append(int(token))
if len(result) == n:
# we get here on last whitespace
break
# and clean for new token
token = bytes()
# Skip whitespace that precedes a token or between tokens.
elif c == png.strtobytes('#'):
# Skip comments to the end of line.
infile.readline()
# If there is no whitespaces after conventional newline
# continue reading token
elif c.isdigit():
token += c
else:
raise png.Error('unexpected character %s found ' % c)
return result