[Xorg] Implementing "Xv" extension on DDX which don'tsupportit in hardware...

John Dennis jdennis at redhat.com
Mon Jul 12 10:43:57 PDT 2004

> > > Are the "Xv" overlays _required_ to leave the underlying framebuffer
> > > contents intact ?
> > 
> > No, most XV implementations paint a color key on the underlying
> > framebuffer,
> Who paints the color key ? The server-side part of "Xv" ?

Typically its the background pixel color of the Xv client application.

> Would it be possible to implement a "generic" codepath in Xv which
> renders the image using PutImage when there is no special support for Xv
> in the DDX ?

I used to work for a company that made set-top boxes running Linux and X
Windows. There are two basic problems with this approach we ran into.
Most video sources deliver their image data as YUV, not RGB, so you
would need color space conversion prior to PutImage (actually the shared
memory variant). It was a challenge with commodity hardware of about 2
years ago to do 30 FPS of color space conversion and PutImage operations
especially if the CPU was also decoding the video from a MPEG stream
(Linux 2.4 kernel scheduling was probably also a culprit). Devices which
support YUV framebuffers help enormously.

John Dennis <jdennis at redhat.com>

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