Proposal for per-CRTC pixmaps in RandR

Andy Ritger aritger at
Fri Mar 12 17:11:33 PST 2010

On Fri, 12 Mar 2010, Keith Packard wrote:

> * PGP Signed by an unknown key
> On Fri, 12 Mar 2010 16:03:56 -0800 (PST), Andy Ritger <aritger at> wrote:
>> Don't you have the rendering engine size limits regardless of whether
>> a composite manager has created scanout pixmaps and is compositing into
>> them, or if the X server does so implicitly?
> Yes, the rendering limits are still here, but because we aren't creating
> a giant screen pixmap, we don't need to deal with them. Of course, if
> the application creates a window which spans both monitors, the back
> buffer will be larger than the rendering engine can deal with and we'll
> be in software fallback land (and loving it).

OK, thanks.  The piece I was missing before was that you planned to
fallback to software if the window was larger than the rendering engine's
max buffer size.  That seems like a steep cliff in a common case, but
I won't argue.

> The goal is to make multiple monitors work reasonably, not to make large
> applications work reasonably.
> Frankly, large applications are a DRI issue, not an X issue anyway, once
> DRI has a way to split drawing across buffers, getting that added to X
> is trivial. The nice thing here is that we don't have to use that for
> the multiple monitor case, we can just use different scanout buffers.
>> I'd think that per-head information (list of modes, available rotations,
>> etc) could be queried separately like today, and then the client would
>> construct a description of the desired multi-mode configuration.
>> The client could either just request that the multi-mode config be set
>> (and the implementation would fail if the config was invalid), or the
>> client could optionally ask if the multi-mode config is valid.
> I'm willing to let you guys figure out what you want for this;

Sure; that's fair.

- Andy

> my
> hardware doesn't have any issues with conflicting configurations that I
> know of (now that I can eliminate the whole scanout size thing).
> -- 
> keith.packard at
> * Unknown Key
> * 0x096C4DD3

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