如何让 GTK Cairo 在没有触发事件的情况下多次绘制

Question

我对 GTK 和 Cairo 还很陌生，我需要编写代码，让它在每次调用 gtk_widget_queue_draw 时在 while(1) 循环中绘制我的数据。这是我的尝试：

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

int scrH = 892,  // Window dimensions.
    scrW = 1427,
    type = 0;    // What kind of lines to draw.

int on_draw_event(GtkWidget *widget,
                  cairo_t *cr, 
                  gpointer user_data) {
  cairo_set_source_rgb(cr, 0.0, 0.0, 0.0);
  cairo_paint(cr);
  cairo_set_line_width(cr, 0.5);
  if (type == 0) {
    // Plot a few horizontal lines.
    for (int i = 0; i < scrH; i += 10) {
      cairo_set_source_rgb(cr, 0.2, 0.99, 0.2);
      cairo_move_to(cr, (double) 10, i);
      cairo_line_to(cr, (double) (scrW - 10.0), i);
      cairo_stroke(cr);
    }
  } else {
    // Plot a few vertical lines.
    for (int i = 0; i < scrW; i += 10) {
      cairo_set_source_rgb(cr, 0.99, 0.2, 0.99);
      cairo_move_to(cr, (double) i, 10.0);
      cairo_line_to(cr, (double) i, (scrW - 10.0));
      cairo_stroke(cr);
    }
  }

  return 0;
}

void clicked(GtkWidget *widget,
             GdkEventButton *event,
             gpointer user_data) {
  /* This one works, but is useless for my application.
  if (event->button == 1) {
    type = 0;
    gtk_widget_queue_draw(widget);
  } else if (event->button == 3) {
    gtk_widget_queue_draw(widget);
    type = 1;
  } //TEST */

  /* This one only plots once, not many times. How can I fix it?
  while (1) {
    if (++type == 2) { type = 0; }

    // This was a failed attempt to fix it. It too only plotted a single time.
    // gdk_threads_add_idle((GSourceFunc)gtk_widget_queue_draw, (void*) widget);
    gtk_widget_queue_draw(widget);
    sleep(1);
  } //TEST*/
}


int main(int argc, char *argv[]) {
  GtkWidget *window;
  GtkWidget *darea;

  gtk_init(&argc, &argv);

  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);

  darea = gtk_drawing_area_new();
  gtk_container_add(GTK_CONTAINER(window), darea);

  gtk_widget_add_events(window, GDK_BUTTON_PRESS_MASK);

  g_signal_connect(G_OBJECT(darea), "draw", 
      G_CALLBACK(on_draw_event), NULL); 
  g_signal_connect(window, "destroy",
      G_CALLBACK(gtk_main_quit), NULL);

  g_signal_connect(window, "button-press-event", 
      G_CALLBACK(clicked), NULL);

  gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
  gtk_window_set_default_size(GTK_WINDOW(window), scrW, scrH); 
  gtk_window_set_title(GTK_WINDOW(window), "Lines");

  gtk_widget_show_all(window);

  gtk_main();
}

对代码长度感到抱歉。图形环境往往是 sesquipedalian！

代码编译为：

gcc -g -o fj testGTK.c `pkg-config --cflags gtk+-3.0 --libs gtk+-3.0`

在 Debian Linux 机器上。细节？好的：uname -a:

Linux Sirius 4.19.0-14-amd64 #1 SMP Debian 4.19.171-2 (2021-01-30) x86_64 GNU/Linux

Answer 1

GTK 使用事件循环。当你调用gtk_main() 时，它会启动这个循环，它处理点击事件、绘制你的窗口等。这个想法是每当事件发生时循环调用你的函数。您的函数会处理它，然后将控制权返回给主循环，以便它可以处理更多事件。

您的 while(1) 循环永远不会将控制权返回给主循环，因此不会再处理任何事件 - 包括您在循环内排队的绘制事件。 （gtk_widget_queue_draw() 不会立即重绘小部件；它会为下一个循环安排重绘）。

要解决此问题，请尝试使用g_timeout_add()，而不是使用sleep() 调用的while(1) 循环。作为主循环的一部分，这将每隔 interval 毫秒调用一个函数。