The right tool to use: XGetImage or Compositing or something else entirely

[Nathan Kidd]

On 11-02-23 03:19 PM, Philip Lawatsch wrote:
>>> What I'm trying to do is write some support to use an nvidia "optimus"
>>> system under linux (basically one has two graphics cards, but only one
>>> of the is connected to physical displays).
>
>>> So, any suggestions / advice / best practices (other than not buying
>>> hardware like that) for how I should try to speed that up?
>>
>> http://airlied.livejournal.com/71734.html
>
> Sadly this was for an ati card where open source drivers are available
> to play around with. In my case I can't really hack around in the
> driver :(
> And I don't want to use nouveau as I'm out for opengl performance, so
> I have to use the nvidia binary blobs.

VirtualGL does what you're generally trying to do:

Essentially: GL render to pbuffer -> glReadPixels() -> XShmPutImage() 
should be faster than XGetImage/XPutImage since they avoid moving pixels 
over the X transport.

-Nathan