input transformations

[Keith Packard]

On Thu, 2007-02-01 at 18:26 -0500, David Reveman wrote:
> I spent some time this week trying to add support for input
> transformations to the server. I tried a few different approaches. The
> patches I've attached are what's currently working best for me.

Thanks for getting started on this; I believe this is the largest
remaining problem with a composited desktop.

> In this approach I allow every window to have it's own root window
> coordinate space. A window's root window coordinate space is affected by
> all it's ancestors. Composite clients can set a triangular mesh that
> maps root window coordinates from a composite window to one of its
> redirected child-windows. Event coordinates are generated in the event
> windows root coordinate space.

I was thinking we'd want a quad mesh instead of a tri mesh so we could
represent projective transforms, but otherwise, this stuff looks like
it's moving in the right direction. Note that Deron Johnson is working
in this space from an entirely different direction (for looking glass);
I asked him to try and construct an interface layer within the server
that would allow both the polygonal decomposition mechansim and their
own java adventures.

> The compositing manager can make a decent guess
> from the window location but without any hint telling the compositing
> manager which top-level window it's related to, it's hard.

Let's work out what the problems are and start experimenting with
changing toolkits to solve this correctly. Obviously having heuristics
which work for legacy apps will be necessary, but I don't want to rely
on guess work when applications can provide definitive answers.

-- 
keith.packard at intel.com
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