On Mon, 20 Apr 2015 10:13:34 +0200 Michal Suchanek <hramr...@gmail.com> wrote:
> On 20 April 2015 at 09:36, Pekka Paalanen <ppaala...@gmail.com> wrote: > > On Sun, 19 Apr 2015 09:46:39 +0200 > > Michal Suchanek <hramr...@gmail.com> wrote: > > > >> So the device is always absolute and interpretation varies. > > > > I disagree. > > > > Let's take a mouse, optical or ball, doesn't matter. What you get out > > is a position delta over time. This is also know as velocity. Sampling > > rate affects the scale of the values, and you cannot reasonably define > > a closed range for the possible values. There is no home position. All > > There is a home position. That is when you do not move the mouse. The > reading is then 0. That is not a unique position, hence it cannot be a home position. That is only a unique velocity. By definition, if your measurement is a velocity, it does not directly give you an absolute position. When we talk about absolute, we really mean absolute position. > > A mouse could be an absolute device only if you were never able to lift > > it off the table and move it without it generating motion events. This > > is something you cannot do with an absolute device like a joystick. > > You are too much fixed on the construction of the sensor. Mouse is a > velocity sensor similar to some nunchuck or whatever device with > reasonable precision accelerometer. That you can and do lift it off > the table is only relevant to how you use such sensor in practice. Accelerometers measure acceleration. Acceleration, like velocity, is not a position. It does not give you an absolute position directly. Thanks, pq _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/wayland-devel
