Sprite transforms in RandR

[Aaron Plattner]

On Sun, Dec 05, 2010 at 08:47:15PM -0800, Keith Packard wrote:
> On Sun, 5 Dec 2010 16:38:52 -0800, Aaron Plattner <aplattner at nvidia.com> wrote:
> 
> > The crtc shadow functions seem obsolete given the new scanout pixmap
> > creation function, but they can be removed in a later ABI.
> 
> So, I was thinking about what happens when your compositing manager
> creates a PCP and then promptly crashes. With the current spec (and
> implementation), you're left staring at a static image of whatever the
> compositing manager stuck into the scanout pixmap. Not very useful.
> 
> Would it make sense to have the system revert to some sensible state
> when the scanout pixmap was destroyed by the client (either explicitly
> or through disconnecting from the server)? If so, what state should it
> revert to? I can envision a fairly simple option:
> 
>  1) Resize the screen to be no smaller than the current crtc mode.
>  2) Configure the crtc to scanout from the screen pixmap at 0,0
> 
> I don't think it will be all that difficult to make this happen, does it
> seem like a better plan than leaving garbage on the screen?

Yes, definitely.  #2 seems easier.  If you also turn on panning so the
whole screen area is accessible, then it seems better than #1 too because
the compositor is probably going to often be the window manager as well, so
#1 may still leave you with windows that you can't get to.  As annoying as
some people find panning, I suspect not being able to recover from a
crashed compositor because they can't get to the start button or whatever
will be more annoying.

Continuing to scan out the pixmap will just make users think their systems
froze.