[maemo-developers] Wishlist (was:Re: N800 and USB host mode)

[From: Daniel Stone]

On Thu, Mar 08, 2007 at 01:17:47PM -0800, ext Daniel Amelang wrote:
> On 3/8/07, Eero Tamminen <eero.tamminen at nokia.com> wrote:
> >[1] There's a bug in Cairo bugzilla about slowness on 16-bit display
> >     when using Render though...
> 
> Although the compositing code could still be better optimized for
> 16-bit displays, the real "bug" there was that they were recompositing
> large surfaces at each scroll step, which will probably never be fast
> unless compositing is hardware accelerated.

Two bugs, really:
  a) the X server doesn't have sensible acceleration for 16-bit dest
     pictures.  I have a preliminary patch for this which I need to get
     back on.
  b) Cairo is dumb.  It could degrade to a 16-bit surface if the target
     is only 16, thus saving a great deal of memory and calculations.
     Also, last I saw, it insisted on pushing every surface as ARGB32,
     rather collapsing the alpha channel down to 1 bit, or removing it,
     if possible.  a8r8g8b8 IN a8r8g8b8 OVER r5g6b5 is an incredibly
     expensive op ...
     (Note that I haven't checked this for a while.)

Cheers,
Daniel
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