C：使用GTk +跟踪鼠标移动

Question

考虑以下代码：

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


static void destroy(GtkWidget*, gpointer);
static gboolean mouse_moved(GtkWidget *widget,GdkEvent *event,gpointer user_data);

int main(int argc, char* argv[]) {

    GtkWidget *main_window;

    // initializing
    gtk_init(&argc, &argv);

    main_window=gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(main_window),"Test");
    gtk_widget_set_size_request (main_window, 500, 300);

    // connect the window with signals
    g_signal_connect (G_OBJECT (main_window), "destroy",G_CALLBACK (destroy), NULL);
    g_signal_connect (G_OBJECT (main_window), "motion-notify-event",G_CALLBACK (mouse_moved), NULL);

    gtk_widget_set_events(main_window, GDK_POINTER_MOTION_MASK);

    // show window
    gtk_widget_show_all (main_window);

    gtk_main();
    return 0;
}


static void destroy(GtkWidget *window,gpointer data) {
    gtk_main_quit ();
}


static gboolean mouse_moved(GtkWidget *widget,GdkEvent *event, gpointer user_data) {

    if (event->type==GDK_MOTION_NOTIFY) {
        GdkEventMotion* e=(GdkEventMotion*)event;
        printf("Coordinates: (%u,%u)\n", (guint)e->x,(guint)e->y);
    }
}

当我从终端运行此代码时，它将打开一个空窗口，并每次打印出鼠标坐标。
这是上一次执行的输出（的一部分）：

Coordinates: (390,17)
Coordinates: (390,18)
Coordinates: (390,18)
Coordinates: (390,18)
Coordinates: (390,18)
Coordinates: (390,19)
Coordinates: (390,19)
Coordinates: (390,19)
Coordinates: (391,22)
Coordinates: (391,22)
Coordinates: (391,22)
Coordinates: (391,22)
Coordinates: (391,22)
Coordinates: (391,22)
Coordinates: (391,22)
Coordinates: (391,23)
Coordinates: (391,23)
Coordinates: (391,23)
Coordinates: (390,23)
Coordinates: (390,23)
Coordinates: (390,23)
Coordinates: (390,23)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,24)
Coordinates: (390,25)
Coordinates: (390,25)
Coordinates: (390,25)
Coordinates: (390,25)
Coordinates: (390,25)
Coordinates: (390,25)
Coordinates: (390,26)
Coordinates: (390,26)
Coordinates: (390,26)
Coordinates: (390,26)
Coordinates: (390,26)
Coordinates: (390,26)
Coordinates: (390,26)
Coordinates: (390,27)
Coordinates: (390,27)
Coordinates: (390,27)
Coordinates: (390,27)
Coordinates: (390,27)
Coordinates: (390,28)
Coordinates: (390,28)
Coordinates: (390,28)
Coordinates: (390,28)
Coordinates: (390,28)
Coordinates: (390,28)
Coordinates: (390,28)
Coordinates: (390,28)
Coordinates: (390,29)
Coordinates: (390,29)
Coordinates: (390,29)
Coordinates: (390,30)
Coordinates: (390,30)
Coordinates: (390,30)
Coordinates: (390,30)
Coordinates: (390,31)
Coordinates: (390,31)
Coordinates: (390,32)
Coordinates: (390,32)
Coordinates: (390,32)
Coordinates: (390,33)
Coordinates: (390,33)
Coordinates: (390,33)
Coordinates: (390,33)
Coordinates: (390,33)
Coordinates: (390,34)
Coordinates: (390,34)
Coordinates: (390,34)
Coordinates: (389,34)
Coordinates: (389,35)
Coordinates: (389,36)
Coordinates: (389,36)
Coordinates: (389,36)
Coordinates: (389,37)
Coordinates: (389,36)
Coordinates: (389,37)
Coordinates: (389,37)
Coordinates: (389,37)
Coordinates: (389,37)
Coordinates: (389,38)
Coordinates: (389,38)
Coordinates: (388,38)
Coordinates: (388,38)
Coordinates: (388,38)
Coordinates: (388,38)
Coordinates: (388,39)
Coordinates: (388,39)
Coordinates: (388,39)
Coordinates: (388,39)
Coordinates: (388,39)
Coordinates: (388,40)
Coordinates: (387,40)
Coordinates: (387,40)
Coordinates: (387,40)
Coordinates: (387,40)
Coordinates: (387,40)
Coordinates: (387,40)
Coordinates: (387,40)
Coordinates: (386,41)
Coordinates: (386,41)
Coordinates: (386,41)
Coordinates: (386,41)
Coordinates: (386,41)
Coordinates: (386,41)
Coordinates: (385,41)
Coordinates: (385,41)
Coordinates: (385,41)
Coordinates: (385,41)
Coordinates: (384,42)
Coordinates: (384,42)
Coordinates: (384,42)
Coordinates: (384,42)
Coordinates: (384,42)
Coordinates: (384,42)
Coordinates: (384,42)
Coordinates: (383,42)
Coordinates: (383,42)
Coordinates: (383,42)
Coordinates: (383,42)
Coordinates: (383,43)
Coordinates: (382,43)
Coordinates: (382,43)
Coordinates: (382,43)
Coordinates: (382,43)
Coordinates: (381,43)
Coordinates: (381,43)
Coordinates: (381,43)
Coordinates: (380,43)
Coordinates: (380,44)
Coordinates: (380,44)
Coordinates: (380,44)
Coordinates: (380,44)
Coordinates: (379,44)
Coordinates: (378,44)
Coordinates: (378,44)
Coordinates: (377,44)
Coordinates: (377,44)

等等...

令我感到困惑的是：怎么会有两个连续的事件拥有相同的坐标？例如，采用以下两行：

Coordinates: (380,44)
Coordinates: (380,44)  

这基本上是说鼠标没有移动（鼠标从（380,44）移到（380,44）），那么怎么可能有移动事件启动第二行输入的处理程序？

---

另一个不太重要且（也许）无关的问题：
为什么这条线是必需的？

gtk_widget_set_events(main_window, GDK_POINTER_MOTION_MASK);

在《 Gtk +开发基础》一书中说：

接下来，您需要在事件框中添加事件掩码，以便它知道小部件将接收的事件类型。表3-3中显示了指定事件掩码的GdkEventMask枚举值。如果需要设置多个值，可以将GdkEventMask值的按位列表传递给gtk_widget_set_events（）。

但是鉴于我们已经有了g_signal_connect（），此调用是否不多余？根据文档：

将GCallback函数连接到特定对象的信号。

该处理程序将在信号的默认处理程序之前调用。

为什么需要两次注册信号？
一次与gtk_widget_set_events()第二次g_signal_connect()？

Answer 1

我尝试直接使用 xev 监视 X 服务器中的鼠标移动，似乎 xorg 报告具有相同坐标但不同时间戳的多个鼠标事件。然而，当使用键盘上的指点杆时，它不会这样做，只能使用触控板或外接鼠标。

我的猜测是，精度实际上更高，但事件是针对屏幕上的像素报告的。这可能会导致驱动程序报告比需要的更多的鼠标事件。