On Tue, Sep 23, 2014 at 09:28:11AM -0700, Dmitry Torokhov 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 the hid-mt behaviour makes sense. Without explicit resolution (and no device sets that anyway, IIRC) any distance value > min tells us only that a tool is within detectable range, but not yet touching. Anything between min/max is only useful as a relative scale, but effectively that [min,max] range could be a metre or a millimeter, we can't know. So a device with a 0/1 range simply has low granularity and is only able to detect whether something is within range or touching the surface. Cheers, Peter > > > > > 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. > > > 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
