Re: how to draw something on GtkDrawingArea when I click a button?

[Tolic Ma <gbstack08 gmail com>]

On Fri, Mar 19, 2010 at 2:46 PM, Claudio Saavedra <csaavedra gnome org>wrote:

> El vie, 19-03-2010 a las 13:34 +0800, Tolic Ma escribió:
> > Hi,everyone!
> >
> > I want to draw something on GtkDrawingArea when I click a GtkButton,but I
> > don't know how to do this...
> >
> > this is my code(it doesn't work...):
> >
> > *void click_button(void){
> gdk_draw_line(drawing_area,drawing_area->style->white_gc,x,y,width+x,height+y);
> > }
>
> You shouldn't draw directly in your callback for the button. Instead,
> you should call gtk_widget_queue_draw() to tell GTK+ to schedule a paint
> of the widget.
>
> How will the widget be painted? GTK+ will tell your code that the widget
> needs to be painted by emitting the GtkWidget::expose-event signal.
> Then, you should connect to that signal and paint in your callback.
>
> Last but no least, don't forget to paint to the GdkWindow of the drawing
> area, since that's the drawable.
>
> More or less (untested code, just for clarity):
>
> *void
> click_button(GtkButton *button, gpointer data)
> {
>   button_clicked = TRUE;
>   gtk_widget_queue_draw (drawing_area);
>   ...
> }
>
> gboolean
> expose_drawing_area (GtkWidget *area,
>                     GdkExposureEvent *event,
>                     gpointer data)
> {
>   ...
>   if (button_clicked) {
>      gdk_draw_line(drawing_area->window,
>                     drawing_area->style->white_gc,x,y,width+x,height+y);
>   }
>   ...
> }
>
> int main(int argc,char *argv[]){
>   ...
>   g_signal_connect(button,"clicked",G_CALLBACK(click_button),NULL);
>
> g_signal_connect(drawing_area,"expose-event",G_CALLBACK(expose_drawing_area),NULL);
>   ...
> }
>
>
> Claudio
>
> --
> Claudio Saavedra <csaavedra gnome org>
>
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Thank you!

I solved my problem by following your instruction.

Thank you very much!!!