GTK +如何绘制到绘图区域

Question

我想在gtk + cairo绘图区域内绘制一些线条(实际上是正弦波),但我无法想出办法.所以我的代码首先定义了绘图区域,该绘图区域有一个函数回调函数,该函数将白色背景绘制到绘图区域本身......此时我想在每次START按钮之后开始绘制一段sin波.按下(按钮有一个回调绘图功能)....所以首先......有可能这样做吗？我错过了什么？谢谢.

    #include <cairo.h>
    #include <gtk/gtk.h>

    int x = 0;
    int x_old = 0;
    float value = 0;
    float value_old = 0;
    GtkWidget *button = NULL;
    GtkWidget *window = NULL;
    GtkWidget *area = NULL;
    GtkWidget *table = NULL;

    static gboolean load_interface(GtkWidget *widget)
    {
     cairo_t *cr;
     cr = gdk_cairo_create(area->window);
     cairo_set_source_rgb(cr, 1, 1, 1);
     cairo_rectangle(cr, 0, 0, 900, 400);
     cairo_fill(cr);
    }

    void draw(GtkWidget *widget)
    {
     cairo_t *cr;
     cr = gdk_cairo_create(widget->window);

     x_old = x;
     x = x + 15;
     value_old = value;
     value = value + 0.25;

     cairo_set_source_rgb(cr, 0, 0, 0);
     cairo_set_line_width (cr, 1);
     cairo_move_to(cr, x_old, 100 + (sin(value_old))*50);
     cairo_line_to(cr, x, 100 + (sin(value))*50);
     cairo_stroke(cr);
    }


     int main (int argc, char *argv[])
    {
      g_log_set_handler ("Gtk", G_LOG_LEVEL_WARNING, (GLogFunc) gtk_false, NULL);
      gtk_init (&argc, &argv);
      g_log_set_handler ("Gtk", G_LOG_LEVEL_WARNING, g_log_default_handler, NULL);

      window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
      gtk_container_set_border_width (GTK_CONTAINER (window), 3);
      gtk_window_set_title (GTK_WINDOW (window), "Draw");
      gtk_window_set_position (GTK_WINDOW (window), GTK_WIN_POS_CENTER);
      gtk_widget_realize (window);
      g_signal_connect (window, "destroy", gtk_main_quit, NULL);

      table = gtk_table_new (10, 10, TRUE);
      gtk_table_set_col_spacings(GTK_TABLE(table),10);
      gtk_table_set_row_spacings(GTK_TABLE(table),5);
      gtk_container_add (GTK_CONTAINER (window), table);

      area = gtk_drawing_area_new();
      gtk_signal_connect (GTK_OBJECT(area), "event", G_CALLBACK (load_interface),     (gpointer)area);
      gtk_table_attach_defaults (GTK_TABLE(table), area, 1, 10, 0, 10);

      button = gtk_button_new_from_stock ("START");
      g_signal_connect (G_OBJECT (button), "clicked", G_CALLBACK (draw), (gpointer) window);
      gtk_table_attach_defaults (GTK_TABLE(table), button, 0, 1, 0, 1);

      gtk_widget_show_all (window);
      gtk_main ();

      return 0;
     }

Answer 1

所有绘图都应该在绘图区域绘图事件中进行,调用expose-eventGTK2和drawGTK3.响应单击按钮,您只需更改一些值,您将重复使用这些值来计算绘制的整个场景.更改这些值后,只需使绘图区域无效以强制重绘,即可调用gtk_widget_queue_draw绘图区域.就是这样.

如果绘制场景很昂贵,请记住使用cairo裁剪功能通过仅绘制已更改的内容来提高性能.然后使用then gtk_widget_queue_draw_area而不是gtk_widget_queue_draw来提示有关已更改并需要重绘的区域的提示.

请参阅GtkDrawingArea文档.

顺便说一句,不要使用强制转换GTK_OBJECT(弃用),G_OBJECT而是使用.这使得移植到GTK3更容易.