On Wed, Jan 06, 2010 at 09:49:58AM +0900, Joonyoung Shim wrote: > >> First, what is the purpose of ABS_MT_TOUCH_MAJOR event? I wonder how > >> it is used at userspace side. > > > > In a graphical program it can of course be used as is, but in the specific > > application of creating gesture events, the TOUCH and WIDTH parameters can be > > used to, e.g., approximate finger pressure or distinguish between index finger > > and thumb. With the addition of the MINOR parameters, one can also distinguish > > between a sweeping finger and a pointing finger, and with ORIENTATION, one can > > detect twisting of fingers. > > > >> Should the ABS_MT_TOUCH_MAJOR be the mininum set of events for multi > >> touch? I'm not sure whether this question is valid because of first > >> question. > > > > Each finger packet should have an ABS_MT_TOUCH_MAJOR value. In can be computed > > from various types of sensory input, e.g., the size of the contact area or a > > pressure sensor. > > > > Hmm, I think ABS_MT_TOUCH_MAJOR is similar to ABS_PRESSURE, of course it > can be used other purposes. If the device doesn't support the pressure, > the driver doesn't report ABS_PRESSURE, so if the device cannot get a > touching size of the finger, how can the driver report it? Note that ABS_MT_TOUCH_MAJOR complements ABS_PRESSURE but cannot substitute it. The nature of our fingures usually mean that with increasing pressure the touch size increases as the finger flattens. This is only useful as a relative indicator though, as fingers differ greatly in size. 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
