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

[Brian Jordan]

Brilliant work, Erik! I had a chance to play with your first working
hand scroll, and it's beyond explanation how fun it is to be able to
scroll around using the touchpad without aiming for a gtkScrollBar.

For all to consider: there are two grab buttons. What if one tended to
grab + move *objects*, and the other grabs + moves
*scenes/backgrounds*? From what I've heard, kids tend to have a hard
time left-clicking and dragging with their same hand (as with the
touchpad). So, for applications like Browse, both grab buttons could
still just scroll up/down. But for graphical editors (e.g., layout
programs, Physics, Model, anything with a scene and objects), this UI
behavior may be a real time saver and fun to use. This would require
giving applications the ability to process events from these two
scroll buttons in a way that identifies them separately.

Bravo, sir,
Brian

On Thu, Jul 10, 2008 at 2:39 AM, Erik Garrison <erik at laptop.org> wrote:
> 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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