Re: expose event & pixmap question

[Christian Seberino <seberino spawar navy mil>]

Paul

It is slowly becoming clearer thanks to you. We can draw
on a pixmap which is associated with a window which
is part of a drawing area.

Configure/Expose events that *just* modify pixmaps work
great.  I assume at the end of one of those callbacks
that some hidden routine says, "OK, now we need
to DISPLAY this pixmap on the window" and does it???

The reason I am asking is that I made one of these callbacks
be called at other times when a configure/expose event
was NOT fired -- with gtk_idle_add.  Drawing on a pixmap
does NOT automagically change what is seen on GUI right???
How can I make these changes appear then (outside of a
configure/expose event)??

Sincerely,

Chris





On Thu, Feb 28, 2002 at 11:27:20AM -0500, Paul Davis wrote:
> >gint exposeEventHandler(GtkWidget* widget, GdkEventExpose* event) {
> >   gdk_draw_pixmap(widget->window, widget->style->fg_gc[GTK_WIDGET_STATE(widge
> >t)],
> >      Pixmaps::myPicture, event->area.x, event->area.y,
> >      event->area.x, event->area.y, event->area.width, event->area.height);
> >
> >   return FALSE;
> >};
> >
> >
> >Pixmaps make expose event handlers easy I think because you can just
> >redraw uncovered portion with a single function call as in function above.
> >
> >WHY CAN'T WE REDRAW A PORTION OF THE DRAWING AREA THE SAME
> >WAY AND AVOID NEED FOR PIXMAP?
> 
> because we're shouting?
> 
> its because a Pixmap is a different kind of resource than a
> Window. They are both considered to "drawables" - you can draw things
> on them by calling the gdk_draw_*() functions. However, a pixmap is an
> "offscreen" drawable that is never mapped to the display. A window in
> an "onscreen" drawable that can be mapped to the display. when you
> draw on a window, you are either going to fail (the window is not
> mapped), or the results show up "right away". when you draw in a
> pixmap, the results don't show up till you draw the pixmap into a
> window. 
> 
> a drawing area has a window, not a pixmap, as its drawable. if you
> want something else, then i suspect that the Canvas might be worth
> getting to know.
> 
> does this make it any clearer?
> 
> --p

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