# ----------------------------------------------------------------------------
# pyglet
# Copyright (c) 2006-2008 Alex Holkner
# All rights reserved.
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# modification, are permitted provided that the following conditions
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# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# ----------------------------------------------------------------------------
'''Read GIF control data.
http://www.w3.org/Graphics/GIF/spec-gif89a.txt
'''
__docformat__ = 'restructuredtext'
__version__ = '$Id: gif.py 2496 2009-08-19 01:17:30Z benjamin.coder.smith $'
import struct
from pyglet.image.codecs import ImageDecodeException
class GIFStream(object):
def __init__(self):
self.images = []
class GIFImage(object):
delay = None
class GraphicsScope(object):
delay = None
# Appendix A.
LABEL_EXTENSION_INTRODUCER = 0x21
LABEL_GRAPHIC_CONTROL_EXTENSION = 0xf9
LABEL_IMAGE_DESCRIPTOR = 0x2c
LABEL_TRAILER = 0x3b
def unpack(format, file):
size = struct.calcsize(format)
data = file.read(size)
if len(data) < size:
raise ImageDecodeException('Unexpected EOF')
return struct.unpack(format, data)
def read_byte(file):
data = file.read(1)
if not len(data):
raise ImageDecodeException('Unexpected EOF')
return ord(data)
def read(file):
'''Read a GIF file stream.
:rtype: GIFStream
'''
# 17. Header
signature = file.read(3)
version = file.read(3)
if signature != 'GIF':
raise ImageDecodeException('Not a GIF stream')
stream = GIFStream()
# 18. Logical screen descriptor
(logical_screen_width,
logical_screen_height,
fields,
background_color_index,
pixel_aspect_ratio) = unpack('HHBBB', file)
global_color_table_flag = fields & 0x80
global_color_table_size = fields & 0x7
# 19. Global color table
if global_color_table_flag:
global_color_table = file.read(6 << global_color_table_size)
# <Data>*
graphics_scope = GraphicsScope()
block_type = read_byte(file)
while block_type != LABEL_TRAILER:
if block_type == LABEL_IMAGE_DESCRIPTOR:
read_table_based_image(file, stream, graphics_scope)
graphics_scope = GraphicsScope()
elif block_type == LABEL_EXTENSION_INTRODUCER:
extension_block_type = read_byte(file)
if extension_block_type == LABEL_GRAPHIC_CONTROL_EXTENSION:
read_graphic_control_extension(file, stream, graphics_scope)
else:
skip_data_sub_blocks(file)
else:
# Skip bytes until a valid start character is found
print block_type
pass
block_type = read_byte(file)
return stream
def skip_data_sub_blocks(file):
# 15. Data sub-blocks
block_size = read_byte(file)
while block_size != 0:
data = file.read(block_size)
block_size = read_byte(file)
def read_table_based_image(file, stream, graphics_scope):
gif_image = GIFImage()
stream.images.append(gif_image)
gif_image.delay = graphics_scope.delay
# 20. Image descriptor
(image_left_position,
image_top_position,
image_width,
image_height,
fields) = unpack('HHHHB', file)
local_color_table_flag = fields & 0x80
local_color_table_size = fields & 0x7
# 21. Local color table
if local_color_table_flag:
local_color_table = file.read(6 << local_color_table_size)
# 22. Table based image data
lzw_code_size = file.read(1)
skip_data_sub_blocks(file)
def read_graphic_control_extension(file, stream, graphics_scope):
# 23. Graphic control extension
(block_size,
fields,
delay_time,
transparent_color_index,
terminator) = unpack('BBHBB', file)
if block_size != 4:
raise ImageDecodeException('Incorrect block size')
if delay_time:
# Follow Firefox/Mac behaviour: use 100ms delay for any delay
# less than 10ms.
if delay_time <= 1:
delay_time = 10
graphics_scope.delay = float(delay_time) / 100
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