[PATCHv3] dix: add 3x3 transformation matrix xinput property for multi-head handling

[Peter Hutterer]

On Tue, May 25, 2010 at 11:03:28AM +0200, Peter Korsgaard wrote:
> For absolute input devices (E.G. touchscreens) in multi-head setups,
> we need a way to bind the device to an randr output. This adds the
> infrastructure to the server to allow us to do so.
> 
> positionSprite() scales input coordinates to the dimensions of the shared
> (total) screen frame buffer, so to restrict motion to an output we need to
> scale/rotate/translate device coordinates to a subset of the frame buffer
> before passing them on to positionSprite.
> 
> This is done here using a 3x3 transformation matrix, which is applied to
> the device coordinates using homogeneous coordinates, E.G.:
> 
> [ c0 c1 c2 ]   [ x ]
> [ c3 c4 c5 ] * [ y ]
> [ c6 c7 c8 ]   [ 1 ]
> 
> Notice: As input devices have varying input ranges, the coordinates are
> first scaled to the [0..1] range for generality, and afterwards scaled
> back up.
> 
> E.G. for a dual head setup (using same resolution) next to each other, you
> would want to scale the X coordinates of the touchscreen connected to the
> both heads by 50%, and translate (offset) the coordinates of the rightmost
> head by 50%, or in matrix form:
> 
>    left:            right:
> [ 0.5 0 0 ]     [ 0.5 0 0.5 ]
> [ 0   1 0 ]     [ 0   1 0   ]
> [ 0   0 1 ]     [ 0   0 0   ]
> 
> Which can be done using xinput:
> 
> xinput set-prop <left> --type=float "Coordinate Transformation Matrix" \
>        0.5 0 0 0 1 0 0 0 1
> 
> xinput set-prop <right> --type=float "Coordinate Transformation Matrix" \
>        0.5 0 0.5 0 1 0 0 0 1
> 
> Likewise more complication setups involving more heads, rotation or
> different resolution can be handled.
> 
> Signed-off-by: Peter Korsgaard <peter.korsgaard at barco.com>
> ---

Just wondering - do you have any plans of exposing this as an xorg.conf
option as well? I guess it would be handy, especially for permanent
touchscreen configurations.

Simon's pointer accel integration in xf86XInput.c is probably the best code
to look at and steal the approach.
 
Cheers,
  Peter