On Tue, Sep 23, 2014 at 9:28 AM, Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> wrote: > Hi Benjamin, > > On Tue, Sep 23, 2014 at 10:59:16AM -0400, Benjamin Tissoires wrote: >> Hi Andrew, >> >> On Sep 23 2014 or thereabouts, Andrew de los Reyes wrote: >> > Hi folks, >> > >> > More and more we're seeing touch input devices that support detection of >> > fingers that are above the surface and not touching. We were thinking of >> > writing a kernel patch for one such device. Normally we would indicate >> > distance with ABS_MT_DISTANCE, but we ran into the problem that sometimes >> > the hardware will not be able to report a distance (or will stop reporting >> > a distance when it's too great a number), and we had the (bad) idea to >> > simply report a value or 1 or 255 or something like that when distance is >> > unknown. >> >> FWIW, hid-multitouch already support those devices. >> ABS_MT_DISTANCE is set with a min/max of 0/1 when we detect win8 >> certified panels with hovering capability. By default the spec does not >> provide the distance IIRC, and you only have one byte: InRange. > > Hmm, I missed that and this is unfortunate. The ABS capabilities > advertised by the devices should match their real capabilities. If > device can't properly report distance it should not be using > ABS_MT_DISTANCE/ABS_DISTANCE... > >> >> I think Xorg can deal with that (the touch emulation discards the >> ABS_MT_DISTANCE, but the xorg-evdev driver should be smart enough to not >> take BTN_TOUCH into account). >> >> > >> > Dmitry warned that a similar thing happened with PRESSURE a while ago, and >> > it was a mess as different drivers did different things. >> >> As I said, IIRC, xorg-evdev is fine with that. For generic desktop, we >> have to make sure libinput is aware, and then you only have to handle >> your own xorg chromebook driver. This is not something which scares me >> that much, especially given that this is what hid-multitouch reports >> since the v3.9 kernel. >> libinput is based on a per slot device information, so it is really easy >> to implement if it is not already in place. xorg-Synaptics and xorg-Wacom >> should not be ported to wayland from what I understood, so the mess with >> several implementations can be solved easily. >> >> > >> > We are now wondering if we should come up with a standard way to indicate >> > hover with or without distance (or with distance being optional). Dmitry >> > had the idea for a new tool type, HOVER; FINGER would be for touches that >> > are actually touching. >> >> The tool is still the finger. > > Do we reliably know that it is a finger and not a pen or eraser or some > other tool? If we do then obviously introducing new tool will not fly. On a capacitive sensor, I think we do know, at least for finger vs active stylus. To be fair, I do not spend much time working with styluses, so I may not have the most info. > >> So I am not very happy with having a new >> tool. In the end, it may also disturb older clients which will not know >> what to do with HOVER. >> And the ABS_MT_DISTANCE approach used to be fully retro-compatible >> (assuming that the hovering distance is small enough for the user not to >> detect it). > > Except that if we start getting devices that can actually tell the > distance we'd need special casing 0/1 handling, no? > > Thanks. > > -- > Dmitry > -- > To unsubscribe from this list: send the line "unsubscribe linux-input" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
