Re: efficient use of canvas lines

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

Ian Britten wrote:
> It's a similar case with the gtkpixbuf:  I tried using it once on a
> relatively small arial photo (50M).  After it crashed X and hard-locked
> the machine, I didn't try that again... :-(
> [ FYI - +200M images aren't out of the realm of possibility... ]

I believe gdkpixbuf, built into the upcoming gtk2, fixes at least some
of this. You don't have to render the whole image, you can just do
little bits on an expose or scroll.

> So, we're generally not using any of this clever, advanced GTK stuff, and
> are manually calling gdk_draw_lines(), gdk_draw_rgb_image(), etc. on a
> drawawble ourselves.  (Now I'm trying to figure out how to print what
> we're drawing... Any suggestions?)
> 
> What are others doing, when dealing with large amounts of data?

I did my own imagedisplay widget :-) It's not too hard: just a
GtkDrawingArea, a couple of GtkAdjustments, and some very simple stuff
to map virtual to real coordinates for repainting. You can scroll/zoom
on 800M images pretty well with it, and it has some simple support for
image annotations too.

For printing, I just output postscript and leave all the mess for the
printer to deal with. As long as the user has a nice printer, you're
fine ...

John