GTK 绘图相关函数
1.回调函数configure_event，创建窗口时调用该函数，创建一块新的PIXMAP。
gboolean configure_event(GtkWidget *widget, GdkEventConfigure *event, gpointer data)
{
if(pixmap)
g_object_unref(pixmap); //Create the new pixmap
pixmap = gdk_pixmap_new(widget->window,
widget->allocation.width,
widget->allocation.height,
-1);
//initialize the pixmap --- no need, default with black
/*--------------------------------------------------------------------------
gdk_draw_rectangle(pixmap,
widget->style->white_gc,
TRUE,
0, 0,
widget->allocation.width,
widget->allocation.height);
-----------------------------------------------------------------------------*/
return TRUE;
}
2.回调函数expose_event，这个函数比较重要，它实现区域的重绘。每次当drawing_area的窗口的某块区域被挡住或者最小化后再重现都会自动调用该函数，对失效区域重画。另外，我们也可以自己调用gdk_window_invalidate_rect（）或是gtk_widget_queue_draw_area()等函数来发送一条重绘消息。
gboolean expose_event(GtkWidget *widget,GdkEventExpose *event,gpointer data)
{
//draw the pixmap onto the drawable
gdk_draw_drawable(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;
}