Tablet woes...
For months, everything seemed fine in tablet-on-linux-with-Qt land. Or relatively fine. I could sketch with impunity using Krita 1.x and Krita trunk (unless I tried to paint outside the image itself, that is). A first gentle reminder of the state of tablet support under Linux/X11 came when Naomi wanted to try the Gimp for a change and she noticed that there was an offset of about a hundred pixels between her pointer on screen and where the drawing went. I shrugged and told her she'd better use Krita then.
Then Krita started crashing whenever I tried to use the stylus on my tablet notebook. Lukas Tvrdy suddenly lost tablet support. Cyrille Berger went on to investigate and discovered that we were getting spurious mouse events between the tablet events. Now KOffice is pretty smart in that it tries to map every input device, every individual wacom stylus, art pen or whatever the user has to its own tool. Spurious events that belong to another input device mean that tools started switching in mid-drawing, which in turn deletes the brush engine we were drawing with before we are done drawing. Ouch. A workaround is possible, of course, but workarounds have a nasty habit of coming back to bite the developer in the fleshy parts.
But plain painting with a tablet at least used to work without crashing -- and I have no idea what has changed. And, unfortunately, there is a host of issues with Qt's tablet support anyway: ranging from being hard-coded to certain names in X11.org (stylus and eraser, cursor isn't supported at all), which means Qt effectively doesn't have tablet support on OpenSUSE, to event compression (which means that we don't get all tablet events, which in turn means ugly lines because we cannot track exactly the artist's hand movement.
For reference, these are the Qt issues we're dealing with:
- 193856 - Allow disabling of compression for mouse/tablet events
- 160626 - Tablet events are incorrect when leaving the QWidget
- 187372 - Qt does not recognize all input devices on X11
- 210132 - Qt expects hardcoded wacom device identifiers from xorg.conf
- 207389 - When the tablet device changes after the application has been started, QTabletEvent::device() still refers to the old one
- 193475 - Mac; Graphire 2 tablet stylus device not detected properly
None of them seem close to being closed. The last one is for OS X -- I'm not sure how good the support for tablets on Windows is since I cannot test Krita on Windows with my tablet due to Microsoft messing up their upgrades. (In order to have a Windows in a virtual machine, I first need a Windows installer, and those are not free.)
So... What now? We have basically two choices: try to improve Qt's tablet support and submit a patch to Trolltech (or try to get paid for improving it?), or re-instate our old Krita 1.x tablet code. It had the same problems with detecting devices that aren't called "stylus" and "eraser", but at least we handled the "cursor" device and we managed to handle the event compression very well. Detecting when a user had changed between tablet and mouse was quite buggy, though, in 1.6. And if we resurrect our old code, we can do so for just Krita, or for all of KOffice. Or we could disable the code that maps an input device to a tool instance, but that would suck big time for artists who have gotten used to pan with the mouse and paint with the pen (like me).