On 01/30/2012 01:23 PM, Jussi Pakkanen wrote:

On 01/30/2012 10:35 AM, Henrik Rydberg wrote:

quoted

+INPUT_PROP_SEMI_MT:
+------------------
+Some touchpads, most common between 2008 and 2011, can detect the presence
+of multiple contacts without resolving the individual positions; only the
+number of contacts and the corresponding bounding box is known. For such
+touchpads, the semi-mt property should be set.

A "corresponding bounding box" usually means "a bounding box that 
contains all touches on the touchpad". I've been told (though I have not 
checked it myself) that there are devices that don't do this. They only 
report a bounding box for some subset of touches. If this is the case, 
it should be documented here.

Yeah, I thought Henrik's definition was correct for a long time, but
when Derek Foreman (I think) proposed some patches for the latest
synaptics devices I took a closer look at my semi-mt synaptics trackpad.
The coordinates it gave were locations based on two of the touches. When
three touches are on the touchpad, it gave a bounding box of two of the
touches, and there's no way to tell which two.

-- Chase