Re: [Qemu-devel] [PATCH] sdl zooming

[Stefano Stabellini]

Anthony Liguori wrote:

> Hi Stefano,
> 
> First, really neat patch.


Thank you, this time I spent a considerable amount of time in cleaning
the patch up and testing it so that it would be easier to merge.


> I was looking at this recently myself.  I 
> cannot tell quickly from looking at the code--perhaps not enough 
> caffeine yet this morning.  Is this nearest neighbor with some sort of 
> smoothing mechanism on top?


The smooth==0 is a nearest neighbor algorithm, while the smooth==1 is a
bilinear interpolation.

> 
> In my experiences with scaling VM displays, bilinear interpolation seems 
> to fit the use case here well as it does best from 1.0-2.0x which is 
> more or less what you'll commonly see.
> 
> Bilinear interpolation can be implemented rather effectively on most 
> processors and is usually hardware supported too.  That suggests that 
> using a library is the right approach to avoid maintaining 
> platform-specific code.
> 
> Cairo seems to be a good choice.  It integrates well with SDL and is 
> portable to all of the platforms we care about.  It's a very simple API 
> too for scaling.  We use it in gtk-vnc and it has proven to be very good 
> for this task.
> 
> What do you think?


I think cairo is a good choice for a new qemu gtk-cairo frontend, but I
don't think that mixing cairo and sdl is a good idea.
Among other things they can have pixel format issues, and it seems to me
that cairo is only able to use 32bpp SDL_Surface.
If you really want a library than SDL_gfx should be used instead, but I
think is overkill.