During lock down I thought I would have some fun in my spare time and see if it was possible to create an LC APNG player. I have found an online APNG decoder and the APNG spec which I was following. However I have had minimal success. I can export the images but they are corrupted. I'm thinking it has something to do with the CRC check. Maybe if you guys with much more experience than me have the time you can correct my mistakes and get it going.
The idea was to break up a APNG file and push it through an image object using the APNG parameters.
If anyone has a little spare time and wants to have a bit of fun please download and have a look. But please don't judge the code I was just experimenting.
Thanks
https://stackoverflow.com/questions/187 ... s-with-php
Code: Select all
on mouseUp pMouseButton
put img "elephant.png" into test1
put empty into tPic
put byte 1 to 8 in test1 into tSig
put 8 into toffset
put the len of test1 into tSize
--hex 76f6b354 7796403
repeat until toffset >= tSize
--error break
add 1 to tcounter
put byte toffset+1 to (toffset+4) in test1 into tLength
add 4 to toffset
put byte toffset+1 to (toffset+4) in test1 into tType
add 4 to toffset
// Unpack the length and read the chunk data including 4 byte CRC
--$ilength = unpack('Nlength', $length); --output binary into array $length (convert decimal to binary array)
--$ilength = $ilength['length']; --put the $length into array $ilength['length']
--$chunk = substr($data, $offset, $ilength+4); --get the frame data $offset(from) (to)=($ilength+4) incl 4 byte CRC (remove first 4 bytes from chunk as it is sequence data)
--$offset += $ilength+4; --adds 4 to the offset (why?)(maybe (maybe CRC)get ready for next chunk?)
breakpoint
put binaryDecode("M",tLength,sLength) into pLength --get the chunk lenght of frame
--put tLength into tLength['length']
if tType contains "fdAT" then
put byte toffset+1 to ((toffset+1)+sLength) in test1 into tChunk --get location of frame and save to chunk
--put byte 1 to 4 in tChunk into tChunkSequence
--put binaryDecode("M",tChunkSequence,tChunkSequence) into pLength
--put return & tChunkSequence after fld "seq"
--breakpoint
put byte +5 to -1 in tChunk into tChunk --remove 4 bytes sequence from start of chunk
put sLength-4 into pLength --remove 4 byte sequnce from decimal length
put byte (toffset+1+sLength) to (toffset+sLength+4) in test1 into tCRCTest --test crc
else
put byte toffset+1 to (toffset+sLength+4) in test1 into tChunk --get location of frame and save to chunk
end if
--add 4 to toffset
put toffset + (sLength+4) into toffset
switch
case tType contains "IHDR"
--header
--$header = $length . $type . $chunk;
put byte -4 to -1 in tChunk into tCRC
put binaryDecode("M",tCRC,sCRC) into pCRC
put tLength & tType & tChunk into tHeader
--breakpoint
break
case tType contains "IDAT"
put tLength & tType & tChunk into tIDAT
break
case tType contains "IEND"
breakpoint
put tLength & tType & tChunk into tIEND
break
case tType contains "fdAT"
--put char toffset to toffset+sLength in test1 into tChunk --just data and type should get a crc generated
put "IDAT" before tChunk
--generate crc
put Crc32Str(tChunk)into scrc --hex
--put "0x" before tcrc
--breakpoint
--put binaryDecode("M",tCRCTest,sCRCTest) into pCRCTest
--breakpoint
--put baseConvert(sCRCTest,10,10) into sCRCTest
put baseConvert(scrc,16,10) into tcrc --hex to decimal
put binaryEncode("M",tcrc) into tcrc --deciaml to binary
--put char 11 to -9 of compress(tcrc) into tcrc
--breakpoint
put tcrc after tChunk
--put char -4 to -1 of tChunk into tChunk --remove crc
if fts is "65" then
breakpoint
end if
put binaryEncode("M",pLength) into pLength --encode new length for file
put pLength & tChunk into tPic --minus 4 from the length then convert to binary
--$length . $type . $chunk; (parts)
--$signature . $header . $parts[$i] . $end; (file)
break
case tType contains "fcTL"
--breakpoint
put byte 9 to 12 of tChunk into tw --width 480
put binaryDecode("M",tw,fw) into ptw
put byte 5 to 8 of tChunk into th --height 400
put binaryDecode("M",th,fh) into pth
put byte 1 to 4 of tChunk into ts --sequence 1
put binaryDecode("M",ts,fts) into pts
if fts is "65" then
--breakpoint
end if
put byte 21 to 22 of tChunk into tfnum
put binaryDecode("m",tfnum,fnum) into pfnum
put byte 23 to 24 of tChunk into tdnum
put binaryDecode("m",tdnum,dnum) into pdnum
break
end switch
if tcounter >= 1000 then
exit repeat
end if
end repeat
breakpoint
--$signature . $header . $parts[$i] . $end;
put tSig & tHeader & tPic & tIEND into sPic
set the text of img "test3" to sPic --into img "test3"
put specialfolderpath("desktop") & "/image.png" into theFilepath
open file theFilepath for binary write ## you might also use 'binary update' here to modify part of file
write sPic to file theFilePath
close file theFilePath
end mouseup 
