On Mon, Feb 22, 2016 at 08:35:31AM -0800, Charles Mooney wrote: > On Sun, Feb 21, 2016 at 2:04 PM Peter Hutterer <peter.hutterer@xxxxxxxxx> wrote: > > > > On Thu, Feb 18, 2016 at 10:19:30AM -0800, Dmitry Torokhov wrote: > > > On Tue, Feb 09, 2016 at 01:56:05PM -0800, Charles Mooney wrote: > > > > Hello all, > > > > > > > > I'm currently working with a touchpad vendor with a new device that > > > > supports a limited form of hover detection. Their sensor is able to > > > > detect the presence or absence of a finger/hand/palm hovering over the > > > > sensor without touching it, but is unable to report any more details > > > > about it. This is a more limited form of hover detection than some > > > > devices which attach a hover state to each finger they see, and can > > > > even report x/y coordinates to hovering finger. > > > > > > > > Instead of using ABS_MT_DISTANCE, it appears that the correct event to > > > > use would be ABS_DISTANCE, since the value is not tied to a specific > > > > finger. I would like to check with you all about how this value is > > > > intended to be used, because it's not quite as obvious to me as I > > > > first thought. > > > > > > > > We need to handle three basic states: > > > > 1. At least one finger is touching the pad. > > > > 2. Something is hovering, but nothing is actually touching. > > > > 3. Nothing is touching the pad and nothing is detected hovering over it either > > > > > > > > It's seems clear to me that an ABS_DISTANCE of zero should indicate > > > > state #1 and that any other legal positive value should indicate state > > > > #2, but I'm less clear on what the best way to handle state #3 is. > > > > Currently, I think the best strategy would be to use a value of > > > > ABS_DISTANCE = -1 to indicate that there are no fingers seen (hovering > > > > or otherwise), does that make sense? > > > > > > > > If not this, how else would you suggest that this ought to be done? > > > > > > As we discussed in person, I believe that reporting an "out of bounds" > > > value for ABS_DISTANCE when we have to use single-touch mode and thus do > > > not have a good way to invalidate a contact, is the easiest option. > > > Alternative would be to invent another SYN event, which I'd rather not. > > > > > > So for devices that support hovering but can not report individual > > > hovering contacts we should declare 0..N as ABS_DISTANCE range and report > > > following values: > > > > > > - 0 when a finger is actually touching > > > - 1..N for hovering fingers > > > - return X < 0 or X > N when no fingers are detected at all; in > > > practice I think we should simply report -1 in this case. > > > > > > Benjamin, Peter, Henrik, any concerns? > > > > on the touchpads that support hovering we're already using BTN_TOOL_FINGER > > together with ABS_DISTANCE, without needing out-of-range reports. > > BTN_TOUCH is the signal when a finger is physically touching (or ABS_PRESSURE > > if it exists and clients care about it). > > > > So the sequence Charles should send is: > > > > 3) <nothing> :) > > 2) > > EV_ABS ABS_DISTANCE <d> # for d > 0 > > EV_KEY BTN_TOOL_FINGER 1 > > EV_SYN SYN_REPORT 0 > > 1) > > EV_ABS ABS_DISTANCE 0 > > EV_ABS ABS_X <x> > > EV_ABS ABS_Y <y> > > ... > > EV_KEY BTN_TOUCH 1 > > EV_SYN SYN_REPORT 0 > > 2) > > EV_ABS ABS_DISTANCE <d> # for d > 0 > > EV_KEY BTN_TOUCH 0 > > EV_SYN SYN_REPORT 0 > > 3) > > EV_KEY BTN_TOOL_FINGER 0 > > EV_SYN SYN_REPORT 0 > > > > This should work with at least libinput, though I have to check what happens > > when you don't send x/y on the first event. I think this would need a patch > > in libinput, but that's doable. And it's the same sequence we also use for > > e.g. pen tools that support hovering as well. > > > > Cheers, > > Peter > > Hi Peter, > > It looks like you're suggesting to use "BTN_TOOL_FINGER" as a signal > as to weather or not the value in "ABS_DISTANCE" is valid or not. > > 1. No finger detected anywhere: > BTN_TOOL_FINGER = 0 > ABS_DISTANCE = n/a > 2. Finger seen hovering but not touching: > BTN_TOOL_FINGER = 1 > ABS_DISTANCE > 0 > 2. Finger touching: > BTN_TOOL_FINGER = 1 > ABS_DISTANCE = 0 you should set BTN_TOUCH here. This can be done based on some magic pressure threshold if you have pressure, otherwise just unconditionally set it whenever distance is 0. > > Am I understanding that correctly? yes, but IMO better to think it this way: BTN_TOOL_FINGER signals whether a finger is detected by the device. everything else is just axis information if and when it becomes available. likewise, BTN_TOUCH signals whether the current tool (could be something other than finger) logically touches the surface. Cheers, Peter -- 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
