gtk3.0学习笔记6-自定义绘图

许多小部件，如按钮，都自己做所有的绘图。你只要告诉他们你想要看到的标签，他们弄清楚要使用的字体，绘制按钮轮廓和焦点矩形等。有时，有必要做一些自定义的绘图。在这种情况下，GtkDrawingArea 可能是正确使用的小部件。它提供一个画布，您可以通过连接到“绘制”信号绘制。
小部件的内容通常需要部分或全部重新绘制，例如，当另一个窗口被移动并发现部分小部件时，或者当包含它的窗口被调整大小时。也可以通过调用gtk_widget_queue_draw()或其变体来明确地引起部分或全部小部件的重绘 。GTK +通过为:: draw信号处理程序提供一个即用的开罗上下文来处理大部分细节。
以下示例显示了一个:: draw信号处理程序。它比以前的例子要复杂一点，因为它也通过:: button-press和:: motion-notification处理程序来演示输入事件处理。

示例：响应输入进行绘图

创建一个名为test.c的以下内容的新文件。

#include <gtk/gtk.h>/* Surface to store current scribbles */static cairo_surface_t *surface = NULL;static void clear_surface (void){  cairo_t *cr;  cr = cairo_create (surface);  cairo_set_source_rgb (cr, 1, 1, 1);  cairo_paint (cr);  cairo_destroy (cr);}/* Create a new surface of the appropriate size to store our scribbles */static gboolean configure_event_cb (GtkWidget         *widget,                                    GdkEventConfigure *event,                                    gpointer           data){  if (surface)    cairo_surface_destroy (surface);  surface = gdk_window_create_similar_surface (gtk_widget_get_window (widget),                                               CAIRO_CONTENT_COLOR,                                               gtk_widget_get_allocated_width (widget),                                               gtk_widget_get_allocated_height (widget));  /* Initialize the surface to white */  clear_surface ();  /* We've handled the configure event, no need for further processing. */  return TRUE;}/* Redraw the screen from the surface. Note that the ::draw * signal receives a ready-to-be-used cairo_t that is already * clipped to only draw the exposed areas of the widget */static gboolean draw_cb (GtkWidget *widget,                         cairo_t   *cr,                         gpointer   data){  cairo_set_source_surface (cr, surface, 0, 0);  cairo_paint (cr);  return FALSE;}/* Draw a rectangle on the surface at the given position */static void draw_brush (GtkWidget *widget,                        gdouble    x,                        gdouble    y){  cairo_t *cr;  /* Paint to the surface, where we store our state */  cr = cairo_create (surface);  cairo_rectangle (cr, x - 3, y - 3, 6, 6);  cairo_fill (cr);  cairo_destroy (cr);  /* Now invalidate the affected region of the drawing area. */  gtk_widget_queue_draw_area (widget, x - 3, y - 3, 6, 6);}/* Handle button press events by either drawing a rectangle * or clearing the surface, depending on which button was pressed. * The ::button-press signal handler receives a GdkEventButton * struct which contains this information. */static gboolean button_press_event_cb (GtkWidget      *widget,                                       GdkEventButton *event,                                       gpointer        data){  /* paranoia check, in case we haven't gotten a configure event */  if (surface == NULL)    return FALSE;  if (event->button == GDK_BUTTON_PRIMARY)    {      draw_brush (widget, event->x, event->y);    }  else if (event->button == GDK_BUTTON_SECONDARY)    {      clear_surface ();      gtk_widget_queue_draw (widget);    }  /* We've handled the event, stop processing */  return TRUE;}/* Handle motion events by continuing to draw if button 1 is * still held down. The ::motion-notify signal handler receives * a GdkEventMotion struct which contains this information. */static gboolean motion_notify_event_cb (GtkWidget      *widget,                                        GdkEventMotion *event,                                        gpointer        data){  /* paranoia check, in case we haven't gotten a configure event */  if (surface == NULL)    return FALSE;  if (event->state & GDK_BUTTON1_MASK)    draw_brush (widget, event->x, event->y);  /* We've handled it, stop processing */  return TRUE;}static voidclose_window (void){  if (surface)    cairo_surface_destroy (surface);  gtk_main_quit ();}static voidactivate (GtkApplication *app,          gpointer        user_data){  GtkWidget *window;  GtkWidget *frame;  GtkWidget *drawing_area;  window = gtk_application_window_new (app);  gtk_window_set_title (GTK_WINDOW (window), "Drawing Area");  g_signal_connect (window, "destroy", G_CALLBACK (close_window), NULL);  gtk_container_set_border_width (GTK_CONTAINER (window), 8);  frame = gtk_frame_new (NULL);  gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);  gtk_container_add (GTK_CONTAINER (window), frame);  drawing_area = gtk_drawing_area_new ();  /* set a minimum size */  gtk_widget_set_size_request (drawing_area, 100, 100);  gtk_container_add (GTK_CONTAINER (frame), drawing_area);  /* Signals used to handle the backing surface */  g_signal_connect (drawing_area, "draw",                    G_CALLBACK (draw_cb), NULL);  g_signal_connect (drawing_area,"configure-event",                    G_CALLBACK (configure_event_cb), NULL);  /* Event signals */  g_signal_connect (drawing_area, "motion-notify-event",                    G_CALLBACK (motion_notify_event_cb), NULL);  g_signal_connect (drawing_area, "button-press-event",                    G_CALLBACK (button_press_event_cb), NULL);  /* Ask to receive events the drawing area doesn't normally   * subscribe to. In particular, we need to ask for the   * button press and motion notify events that want to handle.   */  gtk_widget_set_events (drawing_area, gtk_widget_get_events (drawing_area)                                     | GDK_BUTTON_PRESS_MASK                                     | GDK_POINTER_MOTION_MASK);  gtk_widget_show_all (window);}intmain (int    argc,      char **argv){  GtkApplication *app;  int status;  app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);  status = g_application_run (G_APPLICATION (app), argc, argv);  g_object_unref (app);  return status;}

效果图

这节暂时看着还没什么用