What kind of situation trigger the alloc_surface & free_surface function in video.c (video-driver)

[Alex Deucher]

On Wed, Aug 11, 2010 at 10:26 AM, Adam Jackson <ajax at nwnk.net> wrote:
> On Wed, 2010-08-11 at 10:24 +0800, Cui, Hunk wrote:
>> Hi, guys,
>>       Now I am researching about allocate the video overlay memory,
>> some confuse to inquire.
>>       In xf86-video-geode -> lx_video.c -> LXInitOffscreenImages:
>>               alloc_surface = LXAllocateSurface;
>>               free_surface  = LXFreeSurface;
>>
>>       In xf86-video-ati         -> radeon_video.c ->
>> RADEONInitOffscreenImages:
>>               alloc_surface = RADEONAllocateSurface;
>>               free_surface  = RADEONFreeSurface;
>>
>>       Inquire: what kind of situation trigger above functions? What
>> are the mainly effect?
>
> The answer appears to be: nothing.  The alloc_surface hook is never
> called from the core X server.  Which does sort of make me wonder what
> people thought they were writing when they wrote them...
>
> I suspect the intent was to allow XV to offscreen surfaces.

IIRC, these used to be used by the v4l ddx to stream directly to
another Xv adapter, or something like that.  I think xawtv used to use
it back in the day.

Alex