[compiz] Thumbnail plugin

[Dennis Kasprzyk]

> On Wed, 2007-01-24 at 17:25 +0100, Stjepan Glavina wrote:
> > When hovering taskbar, gnome-panel/kicker change the property of the
> > appropriate window ("_NET_WM_SHOW_THUMBNAIL").
> > Thumbnail plugin checks for PropertyNotify events and shows/hides the
> > thumbnail.
>
> (I assume that you didn't want take this discussion off the list)
>
> This discussion should eventually be moved to the wm-spec-list but
> there's a few things I think we should try to decide here first.
>
> 1. Should one window only be allowed to show one thumbnail or should the
> property be a list of thumbnails?
>
> 2. How is the position and scale of the thumbnail encoded. Is it:
>
> data[0] = thumbnail window ID
> data[1] = x
> data[2] = y
> data[3] = width
> data[4] = height
>
> x, y being relative to the client window position.
>
> 3. The compositing manager might have to do some work before it can
> render the requested thumbnail(s) in a client window. The client
> wouldn't want the window which contains thumbnails to be visible until
> all thumbnails can be rendered properly. If the client sets the
> thumbnail property prior to mapping the window, it allows the
> compositing manager to delay any drawing of the client window until the
> requested thumbnails can be rendered. Some of this might need to be
> documented before it can be accepted as an addition to the EWMH spec.
>
> 4. What windows are valid in the thumbnail property? Any window in the
> _NET_CLIENT_LIST root window property? Or should there be a new
> _NET_THUMBNAIL_LIST property? Such a list means that the compositing
> manager doesn't have to provide thumbnails for all available windows,
> which makes sense for the current state where thumbnails for minimized
> windows can't be rendered.
>
> If someone can think of something else, please jump in.
>
> - David
>

I also don't think that rendering the complete thumbnail window (what the 
current state of the thumbnail plugin is) should be the final solution. This 
should be done by the requesting application and the composite manager should 
render only the window thumbnail into it. So here is my idea:

1. We should think about a _NET_CM naming schema, because these are composite 
manager abilities and there may still be separated window and composite 
managers.

2. A window should have a _NET_CM_SUPPORTS (or _NET_CM_PROTOCOLS) list that 
contains all features supported by the composite manager for that window. I 
this case it would be _NET_CM_THUMBNAIL. This could be easily removed if a 
window gets minimized. This list could then be also used to inform a client 
about other features like opacity,brightness,saturation...

3. If a application wants that a thumbnail (or more) should be rendered into 
it's window, it simply sets the _NET_CM_THUMBNAIL atom with a list of the 
thumbnails. 

data[0] = thumbnail window ID
data[1] = x
data[2] = y
data[3] = width
data[4] = height
data[5] = next thumbnail window ID
...

x/y relative to the application window.

Because the composite manager already renders the application window it should 
not be timing issue to render the thumbnails into it. If someone would like 
to create a "switcher like" application outside of the composite manager, 
setting of the thumbnail atom before mapping might be a disadvantage. We 
should also think of a system, how to allow that the opacity, brightness, and 
saturation (or any other supported feature) could be set only for the 
thumbnail.

What do you think about it?

Dennis Kasprzyk