Initial commit.

pngs2apng.py

@@ -0,0 +1,121 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# pngs2apng is python library/executable used for converting multiple pngs
+# into single apng file. It uses only standard python library.
+# Copyright (C) 2016  Pavel Holica, Jiří Kortus
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+
+import sys
+import struct
+import zlib
+
+PNG_HEADER = "".join([chr(x) for x in (137, 80, 78, 71, 13, 10, 26, 10)])
+PNG_HEADER_SIZE = 8
+PNG_IHDR_SIZE = 25 # including length and CRC
+PNG_IEND = "".join([chr(x) for x in (73, 69, 78, 68)])
+PNG_IEND_SIZE = 4
+
+def seek_IDAT(fo):
+    while True:
+        (size, ) = struct.unpack("!I", fo.read(4))
+        frame_type = fo.read(4)
+        if frame_type == "IDAT":
+            return size
+        if frame_type == "IEND":
+            return 0
+        fo.seek(size+4, 1)
+
+def main(target, *inpaths):
+    outfile = open(target, 'w')
+    # write PNG HEADER
+    outfile.write(PNG_HEADER)
+    # copy PNG IHDR from first file
+    with open(inpaths[0]) as first:
+        first.seek(PNG_HEADER_SIZE)
+        outfile.write(first.read(PNG_IHDR_SIZE))
+    # write APNG acTL structure
+    outfile.write(struct.pack("!I", 8)) # size
+    chunk = "acTL"
+    chunk += struct.pack("!I", len(inpaths))
+    chunk += struct.pack("!I", 0)
+    outfile.write(chunk)
+    # CRC
+    outfile.write(struct.pack("!i", zlib.crc32(chunk)))
+    # write frames
+    frame_num = 0
+    for inpath in inpaths:
+        # write APNG fcTL structure
+        outfile.write(struct.pack("!I", 26))
+        chunk = "fcTL"
+        chunk += struct.pack("!I", frame_num)
+        # write frame data from PNG
+        with open(inpath) as infile:
+            # width, height
+            infile.seek(PNG_HEADER_SIZE)
+            ihdr = infile.read(PNG_IHDR_SIZE)
+            size_start = 8
+            size_end = 16
+            chunk += ihdr[size_start:size_end]
+            # x_offset, y_offset
+            chunk += struct.pack("!I", 0)
+            chunk += struct.pack("!I", 0)
+            # delay_num, delay_den
+            chunk += struct.pack("!H", 1000)
+            chunk += struct.pack("!H", 1000)
+            # dispose_op, blend_op
+            chunk += struct.pack("!b", 0)
+            chunk += struct.pack("!b", 0)
+            outfile.write(chunk)
+            outfile.write(struct.pack("!i", zlib.crc32(chunk)))
+            # sequence num + data
+            data_len = 0
+            if frame_num == 0:
+                chunk = "IDAT"
+                while True:
+                    size = seek_IDAT(infile)
+                    if size == 0:
+                        outfile.write(struct.pack("!I", data_len))
+                        outfile.write(chunk)
+                        outfile.write(struct.pack("!i", zlib.crc32(chunk)))
+                        break
+                    chunk += infile.read(size)
+                    data_len += size
+                    infile.seek(4, 1)
+                frame_num += 1
+            else:
+                chunk = 'fdAT'
+                chunk += struct.pack("!I", frame_num+1)
+                while True:
+                    length = seek_IDAT(infile)
+                    if length == 0:
+                        outfile.write(struct.pack("!I", data_len+4))
+                        outfile.write(chunk)
+                        outfile.write(struct.pack("!i", zlib.crc32(chunk)))
+                        break
+                    chunk += infile.read(length)
+                    data_len += length
+                    infile.seek(4, 1)
+                frame_num += 2
+    # write PNG IEND
+    outfile.write(struct.pack("!I", 0))
+    chunk = PNG_IEND
+    outfile.write(chunk)
+    outfile.write(struct.pack("!i", zlib.crc32(chunk)))
+    outfile.close()
+
+if __name__ == "__main__":
+    sys.exit(main(*sys.argv[1:]))