Week 5&6: Krita hackfest

I’m writing this blogpost from Boud’s kitchen. After 10 days of the Krita hackfest I feel quite dizzy. What I was doing?

According the action plan, this two weeks could be spent on some unfinished business. So we decided to work futher on the Adobe Photoshop brush integration. I fixed the type of the brush internally. Photoshop brushes for Krita consist of the alpha-map and the presets of the Photoshop’s brush engine. I ported the GIMP plug-in which loads the bitmaps in the abr brush. But the presets were not parsed.

Frob wrote the python script which I mentioned previously in my blogpost. Frob and Alexandre Prokoudine are working on reverse engineering of the Photoshop’s resources like brushes and gradients. And their work includes also parsing of the brush engines presets. So I ported the script from python to Qt/C++ for Krita. The last step is to integrate the script. That was not done yet.

Then I arrived to Deventer, the Netherlands. Dmitry Kazakov was waiting for me at the airport and we went together to Deventer from Amsterdam. The weekend was gone so fast. We discussed a lot of issues together with Peter Sikking, interaction designer. That was very very interesting for me. I also met other Krita hackers I haven’t met yet like Adam or Vera. It is nice to be together, because you can be very productive.Together with Dmitry we fixed a bug in few minutes. It would take much more time if we would do it like a Report Bug -> Assign -> Fix.

Week 6 was the hackfest for me, Sven, Cyrille and Boud here in Deventer. We decided to give a try to 1/4 computation of the brush mask to have faster painting. This time it was implemented correctly. Before I tried to copy the 1/4 of the mask to the other parts of the mask. This time I decided to compute the brush mask with bi-linear interpolation. I spent 2 days on it fixing some artefacts that started to occur. Final measurements showed that the 1/4 computation is more expensive then the function itself as this time the arctan2 was not involved. Also other benchmark with arctan2 involved showed that the code is equally fast as the version without the interpolation. Maybe some bigger brushes will be faster but I need to investigate. The code is in trunk, we just need to find it’s usage.

Another optimization was for flood fill tool. Write benchmark, valgrind, identify the bottlenecks, try to fix them, do it few times and I was done. Cyrille helped me a lot, he is very good developer and he had always some good advices how to get the speedup. Finally I managed to make flood fill run 3.5 times faster.
Here is table and you can see how time dropped:

Start of the optimization
1. 5,921 msec
2. 5,752 msec
3. 5,574 msec
4. 3,581 msec
5. 1,711 msec
End of the optimization

The flood fill is still quite slow in the Krita. I tested on 4096×4096 pixel image. The performance problem now is that there is difference function used in the flood fill algorithm and the function convert the pixels to LAB. I suppose that in GIMP it is probably done on RGB 8-bit colorspace. But in Krita there are many colorspaces and the best way to do the difference is on L channel in LAB as Cyrille told me.

Then we were in Amsterdam in the Blender studios. We met Ton Roosendaal and the Durian project team. It was exciting for us. I managed to talk with Angela, the Durian artist from Canada. I had nice chat with her, lovely person. I also managed to talk with Ben, the artist who tried Krita and he also produced some art with it. I was in Amsterdam for the first time. I managed to see arrogant Amsterdam bikers, nice architecture and the cannal. We had long but nice walk around the town.

At the hackfest we discovered more performance issues. So I spent some time on smudge brush. I started with simple fixes and I started to work on some complicated issues. I’m writing bitBlt function for our fixed device. Fixed device is used for brush masks and it is faster then using paint device with tiles as the brush masks are usually small and they does not require tiles and undo. We need more function for bitBlt when the selection is stored in fixed device. So far I  the smudge is 1.42x faster.

Krita guys also started to work on various stuff that Peter Sikking proposed, e.g. we have a new widget and scratch box so I had to fix paintops also. Also I rewrote the deform brush. I’m trying to unify the brush engines in Krita and I wanted to add some new features to old brush engines, so rewrite was needed. The code was almost one and a half year old. I did a lot of work on brush engines also. Usually many fixes etc, but that is for other blogpost maybe later.

I would like to thank Boudewijn and Irina for taking care of us. The home-made food was “best thing ever” as Vera would say. I had nice time with the Krita team at Rempt’s house. Thank you for inviting me!

Busy week, I’m really tired and I’m looking forward for some rest and my home.