Re: Redrawing drawing_area

[rsmith xs4all nl]

On 19 Oct, Peter R. Skadhauge wrote:
> Hi,
>
> How can I redraw a drawing area whose content has
> changed? That is, how can I manually trigger a configure_event?

There are at least two ways, but using configure events is not one of them.

You can clear the drawing area with gdk_draw_rectangle, and use the
gdk_draw_* calls on the drawingarea->window, but this can produce visible
flicker.

So what I prefer is to use a pixmap, on which one can also draw using the
gdk_draw_* calls, and then use gdk_draw_pixmap to copy the pixmap to the
drawingarea. The expose callback also does that:

gint 
drawing_area_expose (GtkWidget *widget,
                     GdkEventExpose *event, gpointer data)
{
  gdk_draw_pixmap(widget->window,
                  widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
                  pixmap,
                  event->area.x, event->area.y,
                  event->area.x, event->area.y,
                  event->area.width, event->area.height);
  return FALSE;
}

The pixmap is created in the configure event callback:

gint 
drawing_area_configure (GtkWidget *widget, 
                        GdkEventConfigure *event, gpointer data)
{
  if (pixmap) {
    gdk_pixmap_unref (pixmap);
  }
  pixmap = gdk_pixmap_new (widget->window,
                           widget->allocation.width,
                           widget->allocation.height,
                           -1);
  gdk_draw_rectangle (pixmap,
                      widget->style->black_gc,
                      TRUE,
                      0, 0,
                      widget->allocation.width,
                      widget->allocation.height);
  return TRUE;
}

HTH,
Roland
-- 
Roland Smith                        "When life hands you a lemon,
r s m i t h @ x s 4 a l l . n l      make lemonade."
http://www.xs4all.nl/~rsmith/