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

[Stefano Stabellini]

Anthony Liguori wrote:

> Stefano Stabellini wrote:
>> This patch comes from xen-unstable and adds opengl support for rendering
>> the guest framebuffer in the SDL window.
>> SDL is needed anyway to open the window and handle the events.
>> Opengl rendering is optional and can be turned off at both compile time
>> and run time (--disable-opengl).
>> Some of the benefits of using opengl are:
>>
>> -faster rendering, less CPU intensive, especially with good graphic
>> cards;
>>   
> 
> Have you measured this or is this just intuition?  I've measured it with
> gtk-vnc and I did not observe any CPU usage decrease in using OpenGL for
> rendering verses an XShmImage.


I wrote that because before my patches all the colour conversions were
done in vga_template; after the sdl shared buffer patch the colour
conversions are done by SDL that sadly most of the time still implements
them using CPU based algorithms.
The opengl code should be able to offload all the colour conversions to
the GPU.
So I was referring to SDL vs. OpenGL.

Then there is the video memory versus system memory discussion: the
opengl patch loads the guest framebuffer into video memory then does the
conversion and blitting video->video that should be accelerated.
SDL_CreateRGBSurfaceFrom creates the surface in system memory so the
blitting shouldn't be accelerated.
I am saying should and shouldn't because it also depends on the video
card drivers and the opengl implementation.