Re: [Qemu-devel] [RfC] using pixman in qemu for raster ops

[Stefano Stabellini]

On Tue, 25 Sep 2012, Gerd Hoffmann wrote:
>   Hi,
> 
> While working with the pixman library in the fbdev branch and discussing
> patches with Stefano Stabellini I came to the conclusion that it would
> be a good idea to:
> 
>   (a) use the pixman library not just as vehicle in fbdev,
>       but as core service for all raster ops in qemu.
>   (b) do a major cleanup / revamp of the console system in qemu.
> 
> That implies pixman will join zlib and glib as hard dependency, i.e.
> qemu will stop building without pixman.
> 
> What is pixman?
> 
> As the name implies it is a library for pixel rendering ops.  It is
> portable.  It's used by Xorg, cairo and spice.  On any recent linux
> distro you'll find it already installed.  When you compile qemu with
> spice you'll have a indirect dependency on pixman.  Merging anthonys
> gtk/cairo patches will add another indirect dependency.
> 
> Even though pixman is used by core linux packages it is still a young
> project. On older distros (RHEL-5 for example) it isn't included and
> must be compiled manually.

I think that not being in RHEL5 could create lots of problems for many
people. For example most Xen virtualization products I know today are
based on something from the same era as RHEL5.


> What is the console revamp plan?
> 
>  (1) Drop DisplayAllocator.  Make DisplayChangeListeners support all
>      important formats directly instead (using pixman), then make gfx
>      card emulation use qemu_create_displaysurface_from() to give
>      DisplayChangeListeners direct access to the guests framebuffer.

"important formats" should include 24 bpp (repeating here for people
that didn't follow the other discussion)


>  (2) Replace DisplaySurface with pixman_image_t.  Gives us reference
>      counting for free, which simplifies thread usage in ui/ rendering
>      code.  Also makes it easier to use pixman in ui/ code.
> 
>  (3) Assign a pixman_image_t to each qemu console.  No more redrawing
>      needed on console switching.  vga_hw_invalidate() can be dropped,
>      screendump code can be simplified.
> 
>  (4) API fixes.  DisplayChangeListeners don't get a opaque pointer (or
>      pointer to struct DisplayChangeListener for container_of usage)
>      for example.

opaque pointers are not always necessary or a must have clean up


>  (5) Investigate optimizations.  Such as passing pixman regions to
>      DisplayChangeListensers, so they get all updates in one go instead
>      of being called for each rectangle individually.
> 
> Comments?