Re: ABS_MT_TOUCH_MAJOR metric

[Henrik Rydberg <rydberg@euromail.se>]

Ferruh,

> I understand this works for Dmitry ABS_X, ABS_Y,
> touchscreen reports between 0..A, screen resolution is 0..B, a mapping
> can be done 0..A -> 0..B
> 
> But for ABS_MT_TOUCH_MAJOR how this scaling can be done,
> touchscreen reports between 0..A, do we know the min/max values for
> application side?

You are right to be confused here. The axes you refer to are, in a way,
meaningless because both TOUCH_MAJOR and TOUCH_MINOR (and the corresponding
WIDTH_MAJOR and WIDTH_MINOR) are assumed to be measured in surface coordinates,
i.e., of the same scale as ABS_X and ABS_Y.

Historically, these axes have had specific values anyways, as an indication of
how large a touch area can be a the specific device. This is how userland MT
applications interpret the data. Strictly speaking, this is incorrect, but
that's how it is.

Henrik