Re: On GdkGC, colors, efficiency

[Ian Bell <ian redtommo com>]

On Sunday 15 Jun 2003 9:38 pm, Luca Padovani wrote:
> Hello,
>
> I have been wondering about the following problem for a long time, and
> never got to a conclusion despite of several searches in the m.l.
> archives and gtk+ application sources. If it is a FAQ, well, I have
> missed it :-(
>
> I have a large number of small "elements" to paint on a drawing area,
> each of them with a possibly different color, although in practise there
> will be a farily small number of different colors used. When I say
> "elements" I think of entities which are much more fine-grained than,
> say, GTK widgets. Think of the single words in an HTML document, each
> word being a different element.
>
> Because of the way colors are handled in gdk, I wonder which, among the
> following alternatives, is the best.
>
> a) using only one GdkGC and changing the color before painting any
> element. Note that, if I understand GDK correctly, "changing" involves
> both allocating a color and setting it in the GC. (I suspect at least
> the last operation requires a call to the X server)

I would recommend doing it this way.  The X server overhead for gc changes is 
I believe quite small and may well be combined with your draw request anyway.
>

> b) requesting one new GC for each element. This way I pay the price of
> allocating and setting the color once for each element, every subsequent
> draw operation just reuses the previous GC. In this case I have to store
> the GC in a field of the element. How many GC structures are allocated
> on the X server side? Does the X server (or GDK?) try to cache GCs?

gc caching on the server side is very server dependent so I would not 
recommend trying to obtain large numbers of gcs.

Ian