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

[Jim Gettys <jg@laptop.org>]

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