The details of a FLI file are moderately complex, but the idea behind it is simple: don't bother storing the parts of a frame that are the same as the last frame. Not only does this save space, but it's very quick. It's faster to leave a pixel alone than to set it.
A FLI file has a 128-byte header followed by a sequence of frames. The first frame is compressed using a bytewise run-length compression scheme. Subsequent frames are stored as the difference from the previous frame. (Occasionally the first frame and/or subsequent frames are uncompressed.) There is one extra frame at the end of a FLI which contains the difference between the last frame and the first frame.
byte size name meaning offset 0 4 size Length of file, for programs that want to read the FLI all at once if possible. 4 2 magic Set to hex AF11. Please use another value here if you change format (even to a different resolution) so Autodesk Animator won't crash trying to read it. 6 2 frames Number of frames in FLI. FLI files have a maxium length of 4000 frames. 8 2 width Screen width (320). 10 2 height Screen height (200). 12 2 depth Depth of a pixel (8). 14 2 flags Must be 0. 16 2 speed Number of video ticks between frames. 18 4 next Set to 0. 22 4 frit Set to 0. 26 102 expand All zeroes -- for future enhancement.Next are the frames, each of which has a header:
byte size name meaning offset 0 4 size Bytes in this frame. Autodesk Animator demands that this be less than 64K. 4 2 magic Always hexadecimal F1FA 6 2 chunks Number of 'chunks' in frame. 8 8 expand Space for future enhancements. All zeros.After the frame header come the chunks that make up the frame. First comes a color chunk if the color map has changed from the last frame. Then comes a pixel chunk if the pixels have changed. If the frame is absolutely identical to the last frame there will be no chunks at all.
A chunk itself has a header, followed by the data. The chunk header is:
byte size name meaning offset 0 4 size Bytes in this chunk. 4 2 type Type of chunk (see below).There are currently five types of chunks you'll see in a FLI file.
number name meaning 11 FLI_COLOR Compressed color map 12 FLI_LC Line compressed -- the most common type of compression for any but the first frame. Describes the pixel difference from the previous frame. 13 FLI_BLACK Set whole screen to color 0 (only occurs on the first frame). 15 FLI_BRUN Bytewise run-length compression -- first frame only 16 FLI_COPY Indicates uncompressed 64000 bytes soon to follow. For those times when compression just doesn't work!The compression schemes are all byte-oriented. If the compressed data ends up being an odd length a single pad byte is inserted so that the FLI_COPY's always start at an even address for faster DMA.
The first byte of a compressed line is the number of packets in this line. If the line is unchanged from the last frame this is zero. The format of an individual packet is:
skip_count size_count dataThe skip count is a single byte. If more than 255 pixels are to be skipped it must be broken into 2 packets. The size count is also a byte. If it is positive, that many bytes of data follow and are to be copied to the screen. If it's negative a single byte follows, and is repeated -skip_count times.
In the worst case a FLI_LC frame can be about 70K. If it comes out to be 60000 bytes or more Autodesk Animator decides compression isn't worthwhile and saves the frame as FLI_COPY.
size_count dataIf size_count is positive the data consists of a single byte which is repeated size_count times. If size_count is negative there are -size_count bytes of data which are copied to the screen. In Autodesk Animator if the "compressed" data shows signs of exceeding 60000 bytes the frame is stored as FLI_COPY instead.
The following is an attempt at describing the newer chunks and frames that are not described in the Turbo C FLI library documentation.
Chunk type Chunk ID ---------- ----------- FLI_DELTA 7 (decimal)First WORD (16 bits) is the number of compressed lines to follow. Next is the data for the changing lines themselves, always starting with the first line. Each line is compressed individually.
The first WORD (16 bits) of a compressed line is the number of packets in the line. If the number of packets is a negative skip -packets lines. If the number of packets is positive, decode the packets. The format of an individual packet is:
skip_count size_count dataThe skip count is a single byte. If more than 255 pixels are to be skipped, it must be broken into 2 packets. The size_count is also a byte. If it is positive, that many WORDS of data follow and are to be copied to the screen. If it is negative, a single WORDS value follows, and is to be repeated -size_count times.
Chunk type Chunk ID ---------- ----------- FLI_256_COLOR 4 (decimal)The first WORD is the number of packets in this chunk. This is followed directly by the packets. The first byte of a packet is how many colors to skip. The next byte is how many colors to change. If this number is 0, (zero), it means 256. Next follow 3 bytes for each color to change. (One each for red, green and blue).
The only difference between a FLI_256_COLOR chunk (type 4 decimal) and a FLI_COLOR chunk (type 11 decimal) is that the values in the type 4 chunk range from 0 to 255, and the values in a type 11 chunk range from 0 to 63.
NOTE: WORD refers to a 16 bit int in INTEL (Little Endian) format. WORDS refer to two-bytes (16 bits) of consecutive data. (Big Endian)
Chunk type Chunk ID ---------- ----------- FLI_MINI 18 (decimal) 12 (Hex)From what I understand, this is a miniture 64 x 32 version of the first frame in FLI_BRUN format, used as an button for selecting flc's from within Animator Pro. Simply do nothing with this chunk.
NOTE: When reading the FLI header on the newer FLI and FLC files, the FLI signature bytes are AF12 instead of AF11 used in the older FLI files. Also, you cannot ignore the screen width and height they may not be 320 x 200.
Allowable screen sizes include 320x200, 640x480, 800x600, and 1280x1024.
NOTE: The delay value between frames appears to be in 1000th's of second instead of 70th's.