On Sat, 7 Feb 2004, Suhaib Chishtie wrote:
> I'm trying to make v4l driver to work with chips (Chips and tech
> 69030) x11 driver. The frame grabber can only write directly to
> offscreen video memory in YUV format. But the X11 v4l driver reports
> RGB as the only offscreen image format available. Althoough the chips
> does support both RGB and YUV for offscreen overlays.
>
> Further investigation in chips driver revealed that chips driver is
> registering only RGB as offscreen format and both RGB and YUV as
> supported image format by calling xf86XVListGenericAdaptors and
> xf86XVScreenInit functions.
>
> My question is, What is the difference between offscreen image format
> registered via xf86XVRegisterOffscreenImages and image formats
> registered via calls to xf86XVListGenericAdaptors and
> xf86XVScreenInit?
>
> Almost all of the video drivers register only one (usually YUV) format
> as Offscreen image format and more formats via the screeninit calls.
> If they support overlay in both RGB and YUV formats, should they not
> be registering all the formats as offscreen formats too?
The image formats registered via xf86XVScreenInit are ones that
are exported to the clients. The ones registered via
xf86XVRegisterOffscreenImages are for internal use only. The
idea being that they are the hardware's native overlay format or
formats that can be exposed to other parts of the server such as
a module which uses V4L. Reasons why some formats would be
exposed as client XvImages while they wouldn't be exposed as
OffscreenImages could be:
* The XvImage formats aren't implemented via the overlay, but
with some texture or blit mechanism.
* The XvImage formats, though using the overlay, aren't the native
hardware format and require CPU reformating on the copy.
* There are hardware or software complications related to other
devices bus mastering data into those overlay formats.
* Simply an oversight, or somebody just didn't get around to
adding them, or didn't have a way to adequetly test them.
Mark.
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