[sugar] [PATCH] #447: grab/scroll key

[Erik Garrison]

Sugar devs:

This is a copy of my bug report for #447.  I have completed a first pass
of the grab key implementation.

-Erik


Summary:

I used the grab keys to convert the touchpad into a virtual
mouse scrollwheel. Holding down the grab key and moving the mouse a
small number pixels causes a fake mouse button 4/5/6/7 press, depending
on the direction of motion. This approach works in all applications
which support mouse scroll buttons.

Patches:

The attached patch to sugar-toolkit adds glib/C-side hooks to grab an
ungrab the mouse, and pass motion-notify events to the python side of
the Sugar shell. I have packaged this patch in an rpm which should be
installable on an XO running a recent joyride (tested on joyride-2123). 

(RPMS: tested but slightly older git snapshot:
http://dev.laptop.org/~erik/rpms/sugar-toolkit-debuginfo-0.81.5-4.20080705gitab8c054dfb.fc9.i386.rpm
or, untested but slightly newer git snapshot:
http://dev.laptop.org/~erik/rpms/sugar-toolkit-0.81.6-1.fc9.i386.rpm)

The attached patch to sugar (specifically keyhandler.py) adds the
python-side hooks required to enable the grab/scroll button
functionality.

The patches work in the following manner:

    When the left or right grab buttons are pressed, XGrabPointer is
    called. Subsequently, we capture all of the motion-notify events
    which occur when the user moves the mouse, and each event hits
    KeyHandler._motion_notify_cb() with the coordinates of the mouse.
    After we move N pixels (currently 10) we issue a fake mouse scroll
    button press corresponding to the direction of motion of the mouse
    (4/5/6/7). To issue the fake button press I have found it is
    necessary to ungrab the mouse, issue the press, and then re-grab. 

Known issues:

    In some cases key-releases are not registered. This is problematic
    because without the release signal the mouse grabbing does not
    stop and Sugar becomes entirely unusable. I have not been able to
    establish why, but have noticed that hitting the journal view key
    after Sugar startup before any of the other special keys
    (registered in keyhandler.py) tends to resolve the issue for the
    Super_L and Super_R keys (the grab buttons). 

    The mouse still scrolls around the screen, and the cursor is
    visible during the grab. Solution: Hide the mouse; When a grab key
    press is registered, hide the mouse by setting the cursor pixmap
    to a blank map (and set it back when the grab key release is
    registered). 

    Eventually, after scrolling in one direction, the mouse can move
    out of or to the edge of the scrolling window and the scrolling
    stops. Solution: Every time we issue a fake button press, warp the
    mouse back to the position it was at when we first pressed the
    grab key. 


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