[haiku-appserver] Re: investigating some bugs - Rudolf have a look at this please

  • From: "Rudolf" <drivers.be-hold@xxxxxxxxxxxx>
  • To: haiku-appserver@xxxxxxxxxxxxx
  • Date: Thu, 31 Mar 2005 12:18:18 +0200 CEST

Hi again,

> The backbuffer is in main memory (also on Haiku), for several 
> reasons. 
> Painter can do anti-aliasing, but that would be really slow if the 
> backbuffer would be in graphics mem (because it needs to read from 
> it). 
> Even without anti-aliasing, lots of the drawing_modes need to read 
> pixels. Last but not least, when you alpha blend a bitmap, like 
> something you drag with the mouse, over the backbuffer, it will be 
> much 
> more efficient. I think as long as you don't need to read from the 
> front buffer, having the backbuffer in main memory is just much 
> better.

I agree :)

> >     Doesn't that require the back buffer being inside videoMem?
> >     Rudolf?
> No. Why? You might confuse this with page flipping, but that is not 
> what is happening here. Back and front buffer do not get swapped. 
> They 
> can even have different color spaces. To be more precise, the front 
> buffer can have any colorspace, while the transfer from back to front 
> handles a possible conversion.
Yes, just drawing a bitmap. This is also how it works in swGL. The 
backbuffer sits in mainmem, and is always 32bit space. Drawing this 
bitmap to the frontbuffer colorpspace converts it, and can probably 
even scale it.

(For hwGL I am using a backbuffer in the same space as the frontbuffer 
atm. Backbuffer sits in gfxRAM because the GPU has fastest access to 
both buffers that way (and it's the simplest option from the GPU's 
point of view))

(sorry for keeping mentioning hwGL BTW 8-)


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