On Wed, May 21, 2014 at 10:17 PM, Chandler Paul <[email protected]> wrote: > Hi! Sorry this took so long to write, I've been spending a lot of my > time recently trying to understand the libinput code and all of that > good stuff, and I wanted to make sure I had a decent understanding of it > before I actually wrote up a response. > > On Mon, 2014-04-21 at 19:11 +0200, Carlos Garnacho wrote: >> Hey there!, >> >> Here's a few patches to have libinput handle events from tablets, >> these devices are basically pointer devices, with a varying range >> of extra buttons (either stylus or "pad" buttons), and extra ABS_* >> axes. These devices also often offer information about the stylus >> in use, and its BTN_TOOL_* codes. >> >> So I've gone for reusing and extending libinput_event_pointer, adding >> extra libinput_pointer_axis values, and adding an "axis_frame" event >> to mark the end of a set of simultaneous axis changes, and a "tool_update" >> event to mark tool changes (and delimit proximity). These features are >> only triggered if a new LIBINPUT_DEVICE_CAP_STYLUS capability is set. > I'm with Peter on splitting these up. It seems kind of inconsistent with > the rest of libinput (with what I've gathered, anyway). A > tablet-specific event sounds interesting too, but I feel like > compressing all of the axis changes into. For now I'm going to work on > having all the axis changes reported as separate POINTER_AXIS events. > >> >> Caveats: >> >> * Many of these devices have also tactile strips or wheels, but these are >> unhandled so far... On the devices I've got available for testing, current >> kernel support seems varyingly inconsistent: >> >> - One device has 2 strips, which report on ABS_RX/RY (radial??). Min/max >> are 0..4096, but the reported values are 1,2,4,8,16... So effectively >> a log2 scale, or more graphically a bit shifting over a bunch of 0s, >> which is somewhat more resembling to the physical action on the strip. > Since I'm on a deadline for this and making changes to this in the > kernel would take too long, I don't think I'm going to advocate for > changing this behavior right now. Although I do agree that eventually it > should be changed. Graphically, a bit moving across a field like that > makes sense, but I think that would be a difficult value to make > practical use of in an application without changing it to a simple 1-13 > value. If I get far enough that I can start implementing support for > tactile strips and all those other fancy features some of these tablets > have I might have it convert the values for tactile strips like that to > something more usable by default and leave the other axes as-is. I'm > curious to hear Ping and Jason's opinion on this though, and what kind > of advantages > >> - Another device has one wheel, reported through ABS_WHEEL. Even though >> min/max are reported as [0..1023], on interaction it goes [0..71] (funky >> range too) >> >> We could just forward this as-is, but seems hindering enough to do anything >> useful with those unless that behavior is corrected. >> >> When supported, IMO it'd make sense to have those axes behave similar to >> scroll axes, so the axis value increments or decrements depending on the >> direction. I'm not sure if there would be cases where the absolute value >> matters here? >> >> * One thing worth noting is that axes are currently normalized, to [-1..1] >> for stylus tilt, and [0..1] for everything else. I remember Peter's >> tablet wayland protocol proposal basically forwarded input_absinfo, this >> might not be fully compatible with that, although TBH I'm unsure >> clamping/normalization should take place so high in the stack... > I'm with Peter on this actually. If the axes were used for something > else I might approve of normalization in libinput but I think having > absolute values fits more of the use cases for the extra axes found on > many tablets, especially since Ping said that some of Wacom's in-house > applications actually need these. I do think however, that maybe we > should consider clamping axis values with libinput even if we don't > normalize the axes by default. > > I've forked libinput and I have a branch where I'm fixing up the patches > Carlos sent in based on the feedback from Peter. You can find it here: > > https://github.com/Lyude1337/libinput/tree/carlos_cleanup > > The history is messy on this, but once this is ready to get sent in as > actual patches I'll be rebasing the history. > > Right now I've removed normalization from my branch, but if someone > brings up a good reason to actually have libinput handle that then I can > revert the change. > > Another thing I'm considering regarding this is just having libinput > provide functions/macros for normalizing the values so applications can > normalize the values easily if they want. > > The way I see it is that we want to allow all of the axes to be used how > they were meant used. If Wacom isn't normalizing the values in their > in-house applications I don't think we should either. Again though, I'm > curious to hear Ping and Jason's take on the reasoning for their tablets > sending it's data like this.
I am not an application/toolkit developer. I do not know what kind of values, normalized or not, a Linux toolkit developer would like to receive. Carlos has many years of Gnome/Gtk/Gimp development experience. If he prefers normalizing the values, I think we should consider it. Also, Jason is a big fan of normalization. I trust they both have valid reasons. Ping P.S., the in-house I mentioned before is not Wacom in-house. They are customer in-house applications. Those comments only apply to strips/wheels, not normalization in general. I'll get to the detail in my reply to Carlos. > > Cheers, > Lyude > (a.k.a. Stephen Chandler Paul) > >> * No filtering/hysteresis of coords is done yet. >> >> Cheers, >> Carlos >> >> _______________________________________________ >> wayland-devel mailing list >> [email protected] >> http://lists.freedesktop.org/mailman/listinfo/wayland-devel > _______________________________________________ wayland-devel mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/wayland-devel
