Krita: transactions, swapping and new fastBitBlt for tiled data manager

It was almost two weeks ago when I blogged last time. It was very tough those weeks because I had to merge two processes at the same time: preparations for an examination at the university and coding on Krita. But nevertheless, I'm glad announce much progress in my project for Krita!

Transactions refactoring

I've finally commited my patchset for transactions in Krita [1]. So now there is almost nothing common between Qt's QUndoCommand and Krita's KisTransaction (from the public side :)). It was needed to allow pooler (and upcoming swapper) threads to work efficiently. Now every transaction has the beginning and the end. So when you end a stroke on the canvas you finish a transaction as well. The pooler recognizes this signal and starts doing his routine job to optimize your next stroke (while you are still thinking about it ;)).

There are big changes from a developer point of view as well. Now you can create a transaction in a stack instead of a heap, that makes the code much simplier. And the most curious artefact of Krita's past was removed. There was a "global variable" in every KisDoc2 that used to disable saving undo information while loading the document. This variable had to be checked thoughout all the code of Krita: in every tool, in every action. Now it has gone. New tile engine does initial document loading in a cheap and fast way.

If you are interested in details of the new transactions system you can read a design document here. Examples are given!

Region() interface for paint devices

After finishing with transaction I continued my work on preparation to Filter API redesign. I've added a feature to a paint device for getting a QRegion of non-transparent (non-default) pixels. Of course it is based on tiles, and the region is rounded by 64. It is intended to be used as optimization of filter's application. You can read the details in Filter API Discussion Notes, that happend between Cyrille Berger and me in Deventer.

FastBitBlt interface for paint devices

This is part of Filter API redesign as well. The interface simply shares tiles between different paint devices. It allows us to create clones of devices really fast! It is intended to be used in layer merging subsystem and during filter application. There are limitation in this interface as well: it cannot be used when paint devices are shifted and when their color spaces do not coincide.

Framework for tile compression

After some discussion with Cyrille and his experiments with LZF algorithm, I started implementing tile compression framework inside the tile engine (Cyrille has already added nessecary features into KoStore to allow delegating compression to it). I'm going to kill two rabbits with one shoot, by doing this. The first "rabbit": Krita will be able to work with various formats of saved tiles. It means that we will be able to modernize the tile format without losing back compatibility. And the second: this framework will be the first stone in the swapper subsystem's building!