Re: [PATCH v2] Documented input device properties.

Dmitry Torokhov [off-list ref] writes:

quoted

+INPUT_PROP_POINTER:
+------------------
+There is a one to one mapping between the device coordinates and
+screen coordinates.

This is not correct as touchpads fall firmly into INPUT_PROP_POINTER
land and certainly do not have 1:1 relationship between on-screen and
device coordinates.

quoted

This property only has meaning for non-touch based
+input such as a pen or an eraser. A drawing tablet would have this property
+set.

Wacom Bamboo touch can be said is touch based but still is a pointer
device. Basically pointer device is one that requires use of an
on-screen pointer to reflect user's movement while with direct devices
touching object itself serves as a pointer to the user.

So, does the above mean something like this?

device         I_P_POINTER  I_P_DIRECT  1:1
===========================================
tablet           present     present    yes
touchpad         present     missing    no
touchscreen      missing     present    yes
<impossible>     missing     missing    no

Jussi Pakkanen [off-list ref] writes:

+INPUT_PROP_POINTER:
+------------------
+
+There does not exist a one to one mapping between the device
+coordinates and screen coordinates.

If I understood Dmitry right, the existence of a 1:1 mapping has nothing
to do with a device being I_P_POINTER: the presence of this property
means that an on-screen pointer is required to reflect the user's
movement.  (In practice, non direct devices probably always require a
pointer, or maybe I just lack imagination.)

This property only has meaning for non-touch based input such as a pen
or an eraser.

And what's its meaning then?  Sorry, maybe it's just me, but I don't
understand such sentences.  In my understanding, a device either carries
a property or not; the meaning of a given property is always the same,
and it's the very role of the documentation to define these meanings.

+INPUT_PROP_DIRECT:
+------------------
+
+The device coordinates can be directly mapped to screen coordinates

Cool.

+(i.e. the opposite of INPUT_PROP_POINTER)

Not cool, according to my interpretation of Dmitry's previous review:
see above.

This property only has meaning for touch-based input.

See my other paragraph above.

Jussi, please don't take this personal!  I'm no expert of this, and I'm
not a native English speaker.  Still I think documentation should be
clear even for such dummies like me, that's why I chimed in.  Hopefully
it isn't considered bikeshedding.
-- 
Thanks,
Feri.