On Mon, 25 Nov 2002, Mark Cuss wrote:
> Mark,
>
> Thanks for the info. I noticed in your list below that the intel 815 / 830
> series chips aren't listed... Is it difficult to implement this
> functionality in software? I don't currently have a copy of the X source,
> but I could download it and give it a try...
Rotation using the "shadow framebuffer" is easy. Rendering goes
into system memory and then is copied rotated to video ram. The one
driver that does this in hardware (silicon motion I think) has the
two framebuffers in video ram. It renders to one in hardware and then
updates the other rotated via hardware.
>
> The ultimate goal, however, is to have the rotate supported on the 815 / 830
> chips in hardware. The application that we plan to use displays decoded
> MPEG2 that does a bunch of XvPutImage calls which would likely be pretty
> slow if the X server had to rotate each frame in software. I'm thinking
> that the hardware does support this functionality, as a lot of tablet
> manufacturers are using this hardware in the new "Designed for Windows XP
> Tablet Edition" computers... I was planning to prove them wrong by running
> Linux on one :)
Xv(Shm)PutImage doesn't render to the framebuffer on i815 - the data
goes into the overlay and isn't handled by the shadow framebuffer code.
You'd have to rotate the source for the overlay yourself in software
(easy for 4:2:0, messy for 4:2:2).
>
> I've been in contact with one of the Tablet manufacturers, and they say that
> the Intel video driver that they're using in Windows does the flipping for
> them... this makes me assume that the Windows driver is flipping a 1 into a
> register somewhere to rotate the image. However, I've looked through the
> i830 data sheet and can't spot anything ...
Unlikely. They probably render into video ram normally and then
copy it with rotation using the texture engine. Video, if using the
overlay, is probably done in software by rotating the source, or they
just fall back to YUV->RGB blits in this case so they don't have to
deal with the overlay.
MARk.
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