Re: Allocating a lot of colors

[John Cupitt <john cupitt ng-london org uk>]

Lokesh Setia wrote:
> First of all, I will like to ask whether drawing_area widget with a
> backing pixmap is the best choice for this?  

Hi Lokesh, the way to do this by hand is to use gdk_rgb_*(). Take a look
at testrgb.c in the gtk source area. 

gdk_rgb_*() does all the horrible X stuff for you: it finds an
appropriate visual, opens a shared memory area (if possible), and takes
care of all the dithering that might be necessary to get nice looking
colour. You just make a big RGB array, and call gdk_draw_rgb_image(). 

It's pretty quick too: I get 10 Mpixels/sec on my (modest) system, so
you should be OK for your 50ms timeslot.

If you want something higher level, then gdk-pixbuf is your baby. It
adds things like rescale and image load and save.

> I will have to call
> gdk_draw_point{s}( ) in this case I guess.
> Second, when the image changes (it does after every 50 msec), colors may
> need to be allocated/deallocated. Doing  gdk_colormap_alloc_color() in a
> loop seems to be a grossly inefficient way of doing this.  Is there any
> other option?  

/me falls over

This will be rather slow :-)

John