Touchscreen : values,unit...

[Arnaud Frigout]

Hello All:

I'm porting Android on an imx51 for a new touchscreen.
I know Android use the touchscreen like an input device but I don't
know what are the values it wants? (X,Y,...) What is the unit? (pixel,
mm...)
Do you know which part of Android read the event file (dev/input/
event) of the touchscreen?
Where can I find a documentattion on this item?

Best regards,

Arnaud Frigout

[Deva R]

> I know Android use the touchscreen like an input device but I don't
> know what are the values it wants? (X,Y,...) What is the unit? (pixel,
> mm...)

It will be (x,y) co-ordinates, where (0,0) being the top-left of the
screen and (max-x, max-y) being the bottom of the screen.

how it works:
- when user taps touch screen, it generates an interrupt and its the
trigger for touch screen driver to read the (x,y) co-ordinate from
touch-screen controller.
touch screen controller returns samples that its h/w calculated. (can
be resistive/capacitive).

Once, x,y coordinates are ready, driver publishes using input_report_abs calls.
its still a black box for me, how OS takes (x,y) from this user event,
maps to a framebuffer locaiton, and do some stuff..

u can refer a sample touch screen driver at
http://git.omapzoom.org/?p=kernel/omap.git;a=blob;f=drivers/input/touchscreen/tsc2007.c

>> Do you know which part of Android read the event file (dev/input/event) of the touchscreen?

EventHub.., "Grand Central Station for events" - as called by android team ;P
./frameworks/base/libs/ui/EventHub.cpp
Link - http://git.omapzoom.org/?p=platform/frameworks/base.git;a=blob;f=libs/ui/EventHub.cpp

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[Dianne Hackborn]

KeyInputQueue.java uses JNI calls to ready the events via EventHub.h.  The KeyInputQueue and associated InputDevice classes do the mapping from raw device coordinates to the screen.

--
Dianne Hackborn
Android framework engineer
hac...@android.com

Note: please don't send private questions to me, as I don't have time to provide private support, and so won't reply to such e-mails.  All such questions should be posted on public forums, where I and others can see and answer them.

[Arnaud Frigout]

Hi Deva R and Dianne Hackborn,

Thanks for the quick reply.

Deva R :
The driver reports BTN_TOUCH, ABS_X, ABS_Y and ABS_PRESSURE.
I know that BTN_TOUCH, ABS_X, ABS_Y must be reported for Android but
is it obligatory for ABS_PRESSURE ?
What's happen if i don't use the PRESSURE?

On the screen in the landscape mode where are X,Y ?
is it like this?
Y<----------------O
|
|
|
V
X

Dianne Hackborn :

What are the minimum and the maximum accepted by Android? (-32 768 à
32 767)
Does Android have an unit for the touchscreen like for the
accelerometer?

Thank you.

Best Regards,
Arnaud Frigout

[Deva R]

Hi,

> The driver reports BTN_TOUCH, ABS_X, ABS_Y and ABS_PRESSURE.
> I know that BTN_TOUCH, ABS_X, ABS_Y must be reported for Android but
> is it obligatory for ABS_PRESSURE ?
> What's happen if i don't use the PRESSURE?

you can see few drivers in <kernel>/drivers/input updating just ABS_X,
ABS_Y, but not ABS_PRESSURE..
I'm not sure of usage of pressure parameter in kernel, it should be optional..

> On the screen in the landscape mode where are X,Y ?
> is it like this?
> Y<----------------O
> |
> |
> |
> V
> X

In platforms i've seen, touchscreen always should give absolute
physical co-ordinates w.r.t panel.
its the job of OS (window server) to process it based on what mode it
currently it is (landscape or portrait mode)..

[Arnaud Frigout]

Hi Deva R,

Do you know what are the minimum and the maximum accepted by Android?
(min=0?)
Is it 16 bits or 32bits?

Thanks you,

Best Regards,
Arnaud Frigout