.CDR File Format – Compressed lists

CorelDRAW drawing

Later RIFF CorelDRAW files keep most of the drawing in a list of type cmpr. Its chunks are compressed together as one zlib stream, and their lengths are moved out into a second one. This page follows libcdr’s reader; the version that started using it is not given there.

Layout

Offsets count from the start of the LIST chunk. Numbers are little-endian.

  1. 0LIST and its length8 bytes
  2. 8List type cmpr4 bytes
  3. 12Compressed size the size of the first zlib stream4 bytes
  4. 16Unknown three 32-bit numbers libcdr steps over12 bytes
  5. 28Signature CPng4 bytes
  6. 32Two numbers 16-bit 1 and 16-bit 4; libcdr checks both4 bytes
  7. 36Chunks a zlib stream of the compressed sizevaries
  8. …Block lengths a zlib stream, to the end of the listvaries
A compressed list. The three unknown numbers may be the sizes of the inflated chunks and of the two forms of the block lengths; the explorer says so when one of them matches.

Block lengths

The second stream inflates to a table of unsigned 32-bit numbers. Inside the first stream every chunk has the usual eight-byte header, but its length field is an index into this table: a chunk whose length field is n is as long as entry n. libcdr uses the field as it is when it is not a valid index. The length fields of lists inside the compressed list are indexes too.

So the inflated chunks cannot be read on their own: a reader needs both streams. The explorer shows the compressed list’s header and both zlib streams, block by block, and opens the chunks with their table of lengths as a file of their own.