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

[Anthony Liguori <anthony@codemonkey.ws>]

Stefano Stabellini wrote:
> Hi all,
> this patch implements zooming capabilities for the sdl interface.
> A new sdl_zoom_blit function is added that is able to scale and blit a
> portion of a surface into another.
> This way we can enable SDL_RESIZABLE and have a real_screen surface with
> a different size than the guest surface and let sdl_zoom_blit take care
> of the problem.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>   

Hi Stefano,

First, really neat patch.  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?

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?

http://cairographics.org/SDL/

Regards,

Anthony Liguori