Hi all! It's been a few weeks of GSOC and here is what I've been doing.
I spent some time exploring how the current document comparison function works as well as its implementation. It's about a pretty straight forward algorithm seemingly working well in some cases but being not quite satisfactory in other. My initial intention was to deal directly with the algorithm but I was suggested a rather different approach using the rsid (revision save id) functionallity.
Rsid is a unique number attached to each edit session of a document. It helps tracking changes and merging documents and will give an opportunity for a different comparison algorithm. (more info about rsid)
Viewing the rsid as a char attribute (e.g. "bold") I implemented an SvxRsidItem class (like SvxWeightItem for "bold" ) which extends the SfxUInt32Item.
Every time a document is opened/created, the SwDoc constructor initializes the session number (I added a member of the class to store that - nRsid) to a random number. The idea is to use that number every time the content of the document is changed. Currently, I do that in the SwDoc::Insert() method which is called every time new text is inserted. However, this method is called with the last character of every paragraph when a document is opened, which is a bit of a problem but I hope I will resolve that soon. Also, as far as I noticed, it isn't called when text is copy/pasted from the same document...
Currently I am working on saving the rsids in a an ODF document.