Re: [PATCH] input: Add a detailed multi-touch finger data report protocol

Jim Gettys
2008-11-19T16:55:34Z

On Wed, 2008-11-19 at 11:37 -0500, Dmitry Torokhov wrote:
> Hi Henrik,
>
> On Fri, Nov 07, 2008 at 12:15:29PM +0100, Henrik Rydberg wrote:
> > In order to utilize the full power of the new multi-touch devices, a
> > way to report detailed finger data to user space is needed. This patch
> > adds a multi-touch (MT) protocol which allows drivers to report details
> > for an arbitrary number of fingers.
> >
> > BTN_MT_REPORT_PACKET
> >
> > The driver presses this button to indicate the start of a packet of
> > finger data. The button is released after the whole packet has been
> > reported.
> >
> > BTN_MT_REPORT_FINGER
> >
> > The driver presses this button to indicate the start of a new
> > finger. The button is released when the finger has been reported.
> >
> > In order to stay compatible with existing applications, the data
> > reported in a finger packet must not be recognized as single-touch
> > events. Therefore, a specific set of ABS_MT events is used instead.
> >
> > Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
> > ---
> > include/linux/input.h | 12 ++++++++++++
> > 1 files changed, 12 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/input.h b/include/linux/input.h
> > index b86fb55..c82dd42 100644
> > --- a/include/linux/input.h
> > +++ b/include/linux/input.h
> > @@ -590,6 +590,9 @@ struct input_absinfo {
> > #define KEY_NUMERIC_STAR 0x20a
> > #define KEY_NUMERIC_POUND 0x20b
> >
> > +#define BTN_MT_REPORT_PACKET 0x210 /* report multitouch packet data */
> > +#define BTN_MT_REPORT_FINGER 0x211 /* report multitouch finger data */
> > +
> > /* We avoid low common keys in module aliases so they don't get huge. */
> > #define KEY_MIN_INTERESTING KEY_MUTE
> > #define KEY_MAX 0x2ff
> > @@ -642,6 +645,15 @@ struct input_absinfo {
> > #define ABS_TOOL_WIDTH 0x1c
> > #define ABS_VOLUME 0x20
> > #define ABS_MISC 0x28
> > +#define ABS_MT_TOUCH 0x30 /* Diameter of touching circle */
> > +#define ABS_MT_TOUCH_MAJOR 0x30 /* Major axis of touching ellipse */
> > +#define ABS_MT_TOUCH_MINOR 0x31 /* Minor axis of touching ellipse */
> > +#define ABS_MT_WIDTH 0x32 /* Diameter of approaching circle */
> > +#define ABS_MT_WIDTH_MAJOR 0x32 /* Major axis of approaching ellipse */
> > +#define ABS_MT_WIDTH_MINOR 0x33 /* Minor axis of approaching ellipse */
> > +#define ABS_MT_ORIENTATION 0x34 /* Ellipse orientation */
> > +#define ABS_MT_POSITION_X 0x35 /* Center X ellipse position */
> > +#define ABS_MT_POSITION_Y 0x36 /* Center Y ellipse position */
> > #define ABS_MAX 0x3f
> > #define ABS_CNT (ABS_MAX+1)
> >
>
> Sorry for the long silence. I don't think utilizing button events for
> this is a good idea. I'd rather just start reporting extended touch
> events for a finger and signal end of sub-packet with something like
> EV_SYN/SYN_MT_REPORT.

I agree.

Also, I'm still concerned about using elipses. I doubt very much any
hardware will ever be reporting elipses; more likely are parallelograms,
or trapezoids, other simple geometric figures, rather than a center with
size and orientation.

There are reasons Cairo uses aligned traps internally when tessellating
figures....
- Jim

>
--
Jim Gettys <jg@laptop.org>
One Laptop Per Child