Re: On the fly input_set_abs_params changes

[Yann Cantin <yann.cantin@laposte.net>]

Hi, Jian-Jhong

Le 16/07/2012 07:17, Jian-Jhong Ding a écrit :
>> I'm wondering if it's ok to change min/max parameters after registration, and how
>> it should be handled by xorg's evdev.
> 
> I am really intrigued why you have to do this. Some specific feature of
> your device? Can you elaborate more on this?

A video projector project a computer screen on a whiteboard and an eBeam device is
placed on the whiteboard anywhere outside the image. A special pointer moved on the
whiteboard should act as a mouse device. The whole thing act like a giant touchscreen,
an interactive whiteboard.

The device send the pointer's coordinates in his own coordinate system (cartesian).
It can be place anywhere on the whiteboard, typically on a corner for the one i have.

Unlike fixed interactive whiteboard, as the eBeam can be placed anywhere, the coordinates
you got aren't mapped to screen coordinates even remotely (scaled, rotated and most of
the time subject to projection deformation : i plan to use a homography to retrieve screen
coordinates).

So, the driver need to be calibrated, and this can only be done when the device is
in place : get raw coordinate, compute transform, start mapping.

The simplest way to do this is to start the driver without coordinates transformation,
(input_set_abs_params set to raw axis, aka 0,0xFFFF, not corresponding to screen axis)
launch a calibration phase in user space, and reset input_set_abs_params to the computed ones.


-- 
Yann Cantin
A4FEB47F
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