[haiku-appserver] Re: drawing thread
- From: Adi Oanca <adioanca@xxxxxxxxxxxxxx>
- To: haiku-appserver@xxxxxxxxxxxxx
- Date: Mon, 01 Nov 2004 15:15:23 +0200
Rudolf wrote:
> Hi,
>
> ADI wrote:
>
>
>>>The difference between the setup as below, and the triple setup, is
>>>that in the setup below the blit from back to front buffer has to
>>>be
>>>done and completed _during_ retrace (doable I would guess);
>>>While with the triple version you only need to flip during retrace.
>>>Actual drawing from back to 'front' buffer may here be much slower.
>>
>> True. But then again, in the triple buffering schema, don't you
>>need to draw everything in every
>>flippable buffer? Isn't it twice slower?
>
> I guess you have to make sure the shown buffer is upto date in both
> setups. So it doesn't matter then if you update the same buffer over
> and over again, or if you do both alternatively (it's needed never at
> the same time)
I'd dare to say you're wrong.
If you don't update/blit with the same area/rectangle after the page
flip, surely you won't be
having the same image next time when you flip.
Again, I don't see the usefulness in having three buffers. Either way,
you have to blit from the
back buffer to flippsurface #2, and if the flip occurs at this time, it is
exactly the situation
with simple double buffering - page flipping is not useful anymore.
> Maybe it depends on implementation details like 'only updating on
> actual changes made in backbuffer' (or not).
>
>
>
>> What about apps that are directly using the frame buffer? Won't
>>they always draw into the first
>>flippable buffer?
>
> No: back buffer. As far as they are concerned this _is_ the framebuffer
> I'd say. It's up to 'another process' to make that buffer shown after
> the next upcoming retrace.
I'm not entirely sure, but app_server does not know when to blit when a
BDirectWindow is at use.
Dunno, seems complicated when it could be done easy...
bye,
Adi.
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