Re: drawing graphics

[Steven Jenkins <steven jenkins ieee org>]

Ian Britten wrote:
> In addition to using a background pixmap (as suggested), I also 'attach'
> the pixmap to the window (using gdk_window_set_back_pixmap()).
> This way, you never have to deal with expose events (unless you are
> drawing stuff that isn't in your background pixmap).

Interesting. Please indulge some newbie questions. Is 
gdk_window_set_back_pixmap() documented? All I can find is the function 
prototype. Where do I apply it (presumably in the configure_event 
handler where the pixmap is created)? If I use it, do I no longer need 
to use gtk_widget_draw() to generate expose events? What does the last 
argument (parent_relative) mean?

> All in all, this give a very fast and pleasing application.  No flicker,
> no waiting for expose events to be processed, the data is always visible
> (Even when stepping through the debugger! :-) etc, etc.

That's the plan. )-:

> (As you've discovered, trying to draw all your data within every expose
> event is really inefficient, and grinds your app to a standstill if you
> have much data to draw....)

Right. My attempts to do better with pixmaps have also had problems. I 
based my application loosely on the double-buffered clock application in 
 Harlow's book. Instead of re-drawing the entire pixmap and calling 
gtk_widget_draw to expose the entire drawing area, I've been trying to 
change only part of the pixmap and expose only what's changed. I can 
make the brute force version behave predictably but too slowly to be 
useful. So far, I can't make the more optimized version work 
predictably. It's probably my error, but I'd just as soon not have to 
figure it out.

Thanks for any insights.

Steve