On Sun, Apr 19, 2015 at 12:45 AM, Michal Suchanek <hramr...@gmail.com> wrote: > On 18 April 2015 at 16:58, x414e54 <x414...@linux.com> wrote: >>> Hi, >>> >>> then actually mice are absolute not relative. They have two axis that >>> measure absolute ball rotation speed in two directions just like >>> joystick has two axis that measure absolute stick excentricity. >>> >>> Thanks >>> >>> Michal >> >> This is not really constructive to the api but: >> >> Mice are not absolute because they are just measuring movement of a >> surface relative to itself, when you are not moving the mouse there is >> no axis value. > > There is: the value is 0. Which is the same as with properly > calibrated joystick - when you release it it returns to the position > where reading of both axis is 0. > > And that is the interface expected when using a grabbed mouse with > hidden cursor most of the time. > > There is even parallel for removing springs from a joystick in the > mouse world - there were Russian trackballs with really big metal ball > which would keep spinning due to its momentum until stopped. > > You could take the ball out and turn it over and put it >> back in the absolute position of the ball has changed but the mouse >> axis has not. For some ball mice the rollers measure the movement of a > > That's because it measures speed of the ball not its position. When > you roll the ball outside of the mouse it cannot measure it. > >> wheel with small holes inside it, when it moves it breaks the >> connection the chip registers this and uses it to calculate the delta >> for that axis. Optical mice are just taking small images of the >> surface and using that information to calculate a distance moved, >> again relative motion. > > However, the reported value is absolute speed of the mouse as measured > against the surface. There is no more relativity than with measurement > of excentricity of a stick relative to a central position. > >> >> A joystick does not necessarily have 2 axis and in most cases yes they >> are reporting an absolute position of the axis in the driver but it >> does not necessarily mean that the the hardware is absolute. For >> example if a joystick is using the same slotted optical system as the >> ball mice then this would be measuring relative motion and using it to >> calculate the absolute axis value, under some circumstances the >> position could become out of sync until re-calibrated by moving to the >> joystick to the maximum and minimum values for all axes or having it >> automatically re-center. >> >> >> USB HID specifications define a pointer and a mouse as two completely >> different inputs. A mouse can be a used as a pointer because it is >> pushing the cursor around but the pointer points at a specific >> location. > > And there is no practical way to point with a mouse to a specific > location. Nor is there for most joysticks because they are not precise > enough but you technically could map the stick excentricity to screen > coordinates. Similarly a small touchpad has no practical mapping of > touch coordinates to screen coordinates but for a big graphics tablet > or touchscreen surface this can be done. > > The device is never relative, only interpretation of the obtained data is. > > Thanks > > Michal
Rather than waste time on this I will just direct you over the the universal teacher Google. "relative device" is probably the best search term. _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/wayland-devel
