• 绘制

    绘制

    许多插件，比如buttons，自己就做了它们所有的绘制工作。比如你仅仅需要告诉它们你想看到的标签、你想它们使用的字体、绘制按钮的轮廓和焦点矩形。有时候，有必要做些自定义的绘制。在这种情况下，一个 GtkDrawingArea控件可能是正确的选择，这个控件提供了一个画布，在这个画布上你可以绘制并且将其连接到”draw“信号。

    控件的内容常常需要被部分或者全部重新绘制。比如，当另一个窗口控件被移动并且露出控件的一部分，或者当包含它的窗口重新调整大小时，也会导致控件的部分或者全部被重新绘制。通过调用 gtk_widget_queue_draw()或者它的变体，GTK+提供一个现成的cairo给绘制信号从而实现众多细节。

    下面的程序将会展示一个绘制信号句柄。这个例子比之前的略微复杂，因为它也通过button_press和motion_notify句柄显示出输入活动。

    drawingpng

    Example 3. Drawing in response to input

    新建一个名为 example-3.c 的文件，写入如下内容：

    1. #include <gtk/gtk.h>
    3. /* Surface to store current scribbles */
    4. static cairo_surface_t *surface = NULL;
    6. static void clear_surface (void)
    7. {
    8.     cairo_t *cr;
    10.     cr = cairo_create (surface);
    12.     cairo_set_source_rgb (cr, 1, 1, 1);
    13.     cairo_paint (cr);
    15.     cairo_destroy (cr);
    17. }
    19. /* Create a new surface of the appropriate size to store our scribbles */
    20. static gboolean
    21. configure_event_cb (GtkWidget         *widget,
    22.                     GdkEventConfigure *event,
    23.                     gpointer           data)
    24. {
    25.     if (surface)
    26.     cairo_surface_destroy (surface);
    28.     surface = gdk_window_create_similar_surface (gtk_widget_get_window (widget),
    29.                                                  CAIRO_CONTENT_COLOR,
    30.                                                  gtk_widget_get_allocated_width (widget),
    31.                                                  gtk_widget_get_allocated_height (widget));
    33.     /* Initialize the surface to white */
    34.     clear_surface ();
    36.     /* We've handled the configure event, no need for further processing. */
    37.     return TRUE;
    39. }
    41. /* Redraw the screen from the surface. Note that the ::draw
    42. *  * signal receives a ready-to-be-used cairo_t that is already
    43. *   * clipped to only draw the exposed areas of the widget
    44. *    */
    45. static gboolean draw_cb (GtkWidget *widget,
    46.          cairo_t   *cr,
    47.          gpointer   data)
    48. {
    49.     cairo_set_source_surface (cr, surface, 0, 0);
    50.     cairo_paint (cr);
    52.     return FALSE;
    54. }
    56.  /* Draw a rectangle on the surface at the given position */
    57.  static void draw_brush (GtkWidget *widget,
    58.              gdouble    x,
    59.              gdouble    y)
    60.  {
    61.      cairo_t *cr;
    63.      /* Paint to the surface, where we store our state */
    64.      cr = cairo_create (surface);
    66.      cairo_rectangle (cr, x - 3, y - 3, 6, 6);
    67.      cairo_fill (cr);
    69.      cairo_destroy (cr);
    71.      /* Now invalidate the affected region of the drawing area. */
    72.      gtk_widget_queue_draw_area (widget, x - 3, y - 3, 6, 6);
    74.  }
    76.  /* Handle button press events by either drawing a rectangle
    77.  * or clearing the surface, depending on which button was pressed.
    78.  * The ::button-press signal handler receives a GdkEventButton
    79.  * struct which contains this information.
    80.  */
    81.  static gboolean button_press_event_cb (GtkWidget      *widget,
    82.                         GdkEventButton *event,
    83.                         gpointer        data)
    84.  {
    85.      /* paranoia check, in case we haven't gotten a configure event */
    86.      if (surface == NULL)
    87.      return FALSE;
    89.      if (event->button == GDK_BUTTON_PRIMARY)
    90.      {
    91.          draw_brush (widget, event->x, event->y);
    92.      }
    93.      else if (event->button == GDK_BUTTON_SECONDARY)
    94.      {
    95.          clear_surface ();
    96.          gtk_widget_queue_draw (widget);
    98.      }
    100.      /* We've handled the event, stop processing */
    101.      return TRUE;
    103.  }
    105.  /* Handle motion events by continuing to draw if button 1 is
    106.  * still held down. The ::motion-notify signal handler receives
    107.  * a GdkEventMotion struct which contains this information.
    108.  */
    109.  static gboolean
    110.  motion_notify_event_cb (GtkWidget      *widget,
    111.                          GdkEventMotion *event,
    112.                          gpointer        data)
    113.  {
    114.      /* paranoia check, in case we haven't gotten a configure event */
    115.      if (surface == NULL)
    116.      return FALSE;
    118.      if (event->state & GDK_BUTTON1_MASK)
    119.      draw_brush (widget, event->x, event->y);
    121.      /* We've handled it, stop processing */
    122.      return TRUE;
    124.  }
    126.   static void close_window (void)
    127.   {
    128.       if (surface)
    129.       cairo_surface_destroy (surface);
    131.       gtk_main_quit ();
    133.   }
    135.   int main (int   argc, char *argv[])
    136.   {
    137.       GtkWidget *window;
    138.       GtkWidget *frame;
    139.       GtkWidget *da;
    141.       gtk_init (&argc, &argv);
    143.       window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    144.       gtk_window_set_title (GTK_WINDOW (window), "Drawing Area");
    146.       g_signal_connect (window, "destroy", G_CALLBACK (close_window), NULL);
    148.       gtk_container_set_border_width (GTK_CONTAINER (window), 8);
    150.       frame = gtk_frame_new (NULL);
    151.       gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);
    152.       gtk_container_add (GTK_CONTAINER (window), frame);
    154.       da = gtk_drawing_area_new ();
    155.       /* set a minimum size */
    156.       gtk_widget_set_size_request (da, 100, 100);
    158.       gtk_container_add (GTK_CONTAINER (frame), da);
    160.       /* Signals used to handle the backing surface */
    161.       g_signal_connect (da, "draw",
    162.                         G_CALLBACK (draw_cb), NULL);
    163.       g_signal_connect (da,"configure-event",
    164.                         G_CALLBACK (configure_event_cb), NULL);
    166.       /* Event signals */
    167.       g_signal_connect (da, "motion-notify-event",
    168.                         G_CALLBACK (motion_notify_event_cb), NULL);
    169.       g_signal_connect (da, "button-press-event",
    170.                         G_CALLBACK (button_press_event_cb), NULL);
    172.       /* Ask to receive events the drawing area doesn't normally
    173.       * subscribe to. In particular, we need to ask for the
    174.       * button press and motion notify events that want to handle.
    175.       */
    176.       gtk_widget_set_events (da, gtk_widget_get_events (da)
    177.                              | GDK_BUTTON_PRESS_MASK
    178.                              | GDK_POINTER_MOTION_MASK);
    180.       gtk_widget_show_all (window);
    182.       gtk_main ();
    184.       return 0;
    185.   }

    然后在终端输入以下命令用GCC编译程序：

    1. gcc `pkg-config --cflags gtk+-3.0` -o example-3 example-3.c `pkg-config --libs gtk+-3.0`