Re: [Qemu-devel] [PATCH] opengl rendering in the sdl window

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

Jamie Lokier wrote:

> Anthony Liguori wrote:
>> I'd like to see if it really makes a difference performance wise to 
>> render with OpenGL.  I've had good results in the past using software 
>> bilinear interpolation to do scaling.  If OpenGL doesn't provide a 
>> measurable performance advantage, doing it in software may be the right 
>> thing to do.
> 
> Software interpolation, especially bilinear or other filter, is
> relatively slow if you're expanding a lot of pixels e.g. 640x384 to
> 1920x1200.  OpenGL will surely beat it.
> 
> On the other hand, OpenGL can to be relatively slow (in my experience)
> if there is no colour conversion and scaling to do and X11-SHM would
> be a straight 2d blit on the server side.
> 
> In principle OpenGL should as fast as the 2d blit or faster on
> implementations where the image in client app's memory is a
> memory-mapped texture, but that seems to be still a work in progress
> on BSD and Linux.  DRI2 was dropped this summer because the TTM
> texture memory manager was ousted in favour of the GEM texture memory
> manager... and they haven't caught up with each other yet.  You need
> some kind of good shared texture memory to get great speed out of
> OpenGL displaying a texture which is being constantly updated by the
> client app.
> 
> Imho, if there is an OpenGL backend (overlaid on SDL, Xlib, or
> whatever), it should be a switch, for the next few years probably
> defaulting to X11-SHM (or plain X11 when remote), and changing the
> default to OpenGL in a few years when that's working really well
> everywhere.
> 

I agree with you on everything.