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Use frames count instead of delay to check animated GIFs

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There are GIFs with multiple frames and zero delay, but also GIFs with
a single frame and positive delay. The old algorithm failed for this
kind of images.
This commit is contained in:
Bianca Nenciu 2020-10-28 23:59:57 +02:00
parent e4c198a02c
commit f1628c1539
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1 changed files with 25 additions and 18 deletions
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43
lib/fastimage.rb
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@ -578,38 +578,45 @@ class FastImage
# Checks if a delay between frames exists and if it does, then the GIFs is
# animated
def animated?
delay = 0
frames = 0
@stream.read(10) # "GIF" + version (3) + width (2) + height (2)
# "GIF" + version (3) + width (2) + height (2)
@stream.skip(10)
fields = @stream.read(3).unpack("C")[0] # fields (1) + bg color (1) + pixel ratio (1)
# Skip Global Color Table if it exists
if fields & 0x80
# fields (1) + bg color (1) + pixel ratio (1)
fields = @stream.read(3).unpack("CCC")[0]
if fields & 0x80 # Global Color Table
# 2 * (depth + 1) colors, each occupying 3 bytes (RGB)
@stream.skip(3 * 2 ** ((fields & 0x7) + 1))
end
loop do
block_type = @stream.read(1).unpack("C")[0]
if block_type == 0x21
extension_type = @stream.read(1).unpack("C")[0]
size = @stream.read(1).unpack("C")[0]
if extension_type == 0xF9
delay = @stream.read(4).unpack("CSC")[1] # fields (1) + delay (2) + transparent index (1)
break
elsif extension_type == 0xFF
@stream.skip(size) # application ID (8) + version (3)
else
return # unrecognized extension
if block_type == 0x21 # Graphic Control Extension
# extension type (1) + size (1)
size = @stream.read(2).unpack("CC")[1]
@stream.skip(size)
skip_sub_blocks
elsif block_type == 0x2C # Image Descriptor
frames += 1
return true if frames > 1
# left position (2) + top position (2) + width (2) + height (2) + fields (1)
fields = @stream.read(9).unpack("SSSSC")[4]
if fields & 0x80 != 0 # Local Color Table
# 2 * (depth + 1) colors, each occupying 3 bytes (RGB)
@stream.skip(3 * 2 ** ((fields & 0x7) + 1))
end
@stream.skip(1) # LZW min code size (1)
skip_sub_blocks
else
return # unrecognized block
break # unrecognized block
end
end
delay > 0
false
end
private