#8303 NORM 8.2.1: activity switching is slow because of screenshots

[Zarro Boogs per Child]

#8303: activity switching is slow because of screenshots
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 Reporter:  tomeu        |         Owner:  marco        
     Type:  enhancement  |        Status:  new          
 Priority:  normal       |     Milestone:  8.2.1        
Component:  sugar        |       Version:  not specified
 Keywords:  performance  |   Next_action:  communicate  
 Verified:  0            |     Blockedby:               
 Blocking:               |  
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 By showing to the user small thumbnails of the contents of an activity
 screen we can give a quick glance to the contents of that activity without
 having to fully launch it.

 This is currently used only in the journal but could be extended to other
 places in the UI (activity list on the top frame, activity icons in the
 mesh view, invitations, etc)

 As long as we don't use composition (redirect windows to offscreen
 pixmaps), we only keep pixmaps of the visible windows, thus we need to
 keep a thumbnail every time a window is covered (even if partially).

 The process currently used to take the screenshot takes so much CPU that
 slows down many operations in the shell. I think it's because of
 transferring such a big pixmap from graphics to main memory.

 I see two ways how this could be improved:

  - scale down in the server side with XRender, then transfer the smaller
 pixmap to the client,

  - by using XComposite, redirect the window to an offscreen pixmap and
 take the screenshot at a more convenient moment so that it doesn't block
 any other operation.

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Ticket URL: <http://dev.laptop.org/ticket/8303>
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