[webkit-dev] Rendering Video using video overlay rather than on a Cairo surface (Graphics overlay)

Simon Fraser simon.fraser at apple.com
Mon Jun 1 09:00:30 PDT 2009

On Jun 1, 2009, at 12:47 AM, Sriram Neelakandan wrote:

> On Sat, May 30, 2009 at 9:22 PM, Simon Fraser  
> <simon.fraser at apple.com> wrote:
>> Something else you should consider here is ways that the video can  
>> be clipped
>> and transformed.
> Thanks Simon, I forgot that
>> Any solution which naively puts a hardware surface over some rect  
>> where the
>> video is  supposed to be will be broken in many cases.
> Thinking aloud; the only option seems to be is to convert the YUV
> output of the decoder to a RGB surface, which is mapped in to Cairo
> surface;
> this way Webkit is free to do those crazy CSS Transforms;
> YUV to RGB will kill the processor (unless done in HW)
> But for any embedded core running around 300~400MHz this will never
> work for even D1 at 25 fps  (forget HD)
> Now. how can we accelerate this ?
> I assume clip will always translate to a paint / setSize function. So
> that can be handled in HW. Is that right ?

Clipping in hardware is tricky. You have to consider that there may be  
CSS transforms
between the video and its clipping container, so it's not as simple as  
just some rect of
the video being exposed.

> Is there a way to decently accelerate all the video layer CSS  
> transforms ?
> Is it possible to send the Transform down to RenderVideo and then to
> the MediaPlayer ?
> Some chips do provide HW transform functions;

The ACCELERATED_COMPOSITING code path is really what you want.
>> This is exactly what the ACCELERATED_COMPOSITING code path does.  
>> There is
>> currently a Core Animation backend for Mac (GraphicsLayerCA.mm);  
>> you'd have
>> to
>> write a backend for your compositing system if you wish to use this  
>> code
>> path.
> Does this handle the CSS transforms as well ?

Yes. It also allows for 3D transforms, and hardware acceleration  
transitions and
animations of certain CSS properties.


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