Re: gtk performance testing [was Re: GNOME 2.11/2.12 targeting GTK+ 2.8 (ie cairo based)]

[Russell Shaw <rjshaw netspace net au>]

Clemens Eisserer wrote:
> > When you draw a line or a curve using cairo, it is decomposed
> > into trapezoids which are rendered by RENDER.
>
> Sorry if this question is quite naive, but I wonder why cairo seems to
> generate such a large amount of overhead at all - why can't simple
> operations like fills and blits which are the most used  not be
> executed just like it was before switching to cairo just using plain
> x?
>
> I do not mean using cairo+x but furthermore let cairo do stuff that
> can be done using x-core do by x-core and not create trapezoids out of
> every curve?
> Seems I don't get something...

The core things that draw lines and curves have no concept of how to
blend the colour of the drawing to whatever is beneath it, using the
colouring model that Xrender uses. The core colouring model all goes
thru X colour map tables, so you can't do nice simple mathematical
operations on colors.

The idea of cairo is that everything is decomposed (tesselated) into
polygons, then sent to the server for rendering. This means any shape
can be rendered without adding a new X protocol command. However, the
tradeoff is greater bandwidth usage.