XCB的事件处理如何检测C中的ESC键？

Question

我一直在学习 XCB 教程，但我一直卡在这个教程上。在此示例中，程序在您按下 ESC 键时退出。但是在示例代码中，我无法弄清楚 "case 9" 是如何捕获 ESC 键的。我搜索并查看了 xcb.h 和 xproto.h，以及 ASCII table.

我以为我明白了，直到我"case 9"。这是我完全迷路的地方。所以基本上，他们从哪里得到 9？那如何对应 ESC?

这是我正在研究的示例代码：

#include <stdlib.h>
#include <stdio.h>
#include <string.h> 
#include <xcb/xcb.h>

#define WIDTH 300
#define HEIGHT 100 

static xcb_gc_t gc_font_get (xcb_connection_t *c,
                             xcb_screen_t     *screen,
                             xcb_window_t      window,
                             const char       *font_name);

static void text_draw (xcb_connection_t *c,
                       xcb_screen_t     *screen,
                       xcb_window_t      window,
                       int16_t           x1,
                       int16_t           y1,
                       const char       *label)
{
  xcb_void_cookie_t    cookie_gc;
  xcb_void_cookie_t    cookie_text;
  xcb_generic_error_t *error;
  xcb_gcontext_t       gc;
  uint8_t              length;

  length = strlen (label);

  gc = gc_font_get(c, screen, window, "7x13");

  cookie_text = xcb_image_text_8_checked (c, length, window, gc,
                                          x1,
                                          y1, label);
  error = xcb_request_check (c, cookie_text);
  if (error) {
    fprintf (stderr, "ERROR: can't paste text : %d\n", error->error_code);
    xcb_disconnect (c);
    exit (-1);
  }

  cookie_gc = xcb_free_gc (c, gc);
  error = xcb_request_check (c, cookie_gc);
  if (error) {
    fprintf (stderr, "ERROR: can't free gc : %d\n", error->error_code);
    xcb_disconnect (c);
    exit (-1);
  }
}

static xcb_gc_t gc_font_get (xcb_connection_t *c,
                             xcb_screen_t     *screen,
                             xcb_window_t      window,
                             const char       *font_name)
{
  uint32_t             value_list[3];
  xcb_void_cookie_t    cookie_font;
  xcb_void_cookie_t    cookie_gc;
  xcb_generic_error_t *error;
  xcb_font_t           font;
  xcb_gcontext_t       gc;
  uint32_t             mask;

  font = xcb_generate_id (c);
  cookie_font = xcb_open_font_checked (c, font,
                                       strlen (font_name),
                                       font_name);

  error = xcb_request_check (c, cookie_font);
  if (error) {
    fprintf (stderr, "ERROR: can't open font : %d\n", error->error_code);
    xcb_disconnect (c);
    return -1;
  }

  gc = xcb_generate_id (c);
  mask = XCB_GC_FOREGROUND | XCB_GC_BACKGROUND | XCB_GC_FONT;
  value_list[0] = screen->black_pixel;
  value_list[1] = screen->white_pixel;
  value_list[2] = font;
  cookie_gc = xcb_create_gc_checked (c, gc, window, mask, value_list);
  error = xcb_request_check (c, cookie_gc);
  if (error) {
    fprintf (stderr, "ERROR: can't create gc : %d\n", error->error_code);
    xcb_disconnect (c);
    exit (-1);
  }

  cookie_font = xcb_close_font_checked (c, font);
  error = xcb_request_check (c, cookie_font);
  if (error) {
    fprintf (stderr, "ERROR: can't close font : %d\n", error->error_code);
    xcb_disconnect (c);
    exit (-1);
  }

  return gc;
}

int main ()
{
  xcb_screen_iterator_t screen_iter;
  xcb_connection_t     *c;
  const xcb_setup_t    *setup;
  xcb_screen_t         *screen;
  xcb_generic_event_t  *e;
  xcb_generic_error_t  *error;
  xcb_void_cookie_t     cookie_window;
  xcb_void_cookie_t     cookie_map;
  xcb_window_t          window;
  uint32_t              mask;
  uint32_t              values[2];
  int                   screen_number;

  /* getting the connection */
  c = xcb_connect (NULL, &screen_number);
  if (!c) {
    fprintf (stderr, "ERROR: can't connect to an X server\n");
    return -1;
  }

  /* getting the current screen */
  setup = xcb_get_setup (c);

  screen = NULL;
  screen_iter = xcb_setup_roots_iterator (setup);
  for (; screen_iter.rem != 0; --screen_number, xcb_screen_next (&screen_iter))
    if (screen_number == 0)
      {
        screen = screen_iter.data;
        break;
      }
  if (!screen) {
    fprintf (stderr, "ERROR: can't get the current screen\n");
    xcb_disconnect (c);
    return -1;
  }

  /* creating the window */
  window = xcb_generate_id (c);
  mask = XCB_CW_BACK_PIXEL | XCB_CW_EVENT_MASK;
  values[0] = screen->white_pixel;
  values[1] =
    XCB_EVENT_MASK_KEY_RELEASE |
    XCB_EVENT_MASK_BUTTON_PRESS |
    XCB_EVENT_MASK_EXPOSURE |
    XCB_EVENT_MASK_POINTER_MOTION;
  cookie_window = xcb_create_window_checked (c,
                                             screen->root_depth,
                                             window, screen->root,
                                             20, 200, WIDTH, HEIGHT,
                                             0, XCB_WINDOW_CLASS_INPUT_OUTPUT,
                                             screen->root_visual,
                                             mask, values);
  cookie_map = xcb_map_window_checked (c, window);

  /* error managing */
  error = xcb_request_check (c, cookie_window);
  if (error) {
    fprintf (stderr, "ERROR: can't create window : %d\n", error->error_code);
    xcb_disconnect (c);
    return -1;
  }
  error = xcb_request_check (c, cookie_map);
  if (error) {
    fprintf (stderr, "ERROR: can't map window : %d\n", error->error_code);
    xcb_disconnect (c);
    return -1;
  }

  xcb_flush(c);

  while (1) {
    e = xcb_poll_for_event(c);
    if (e) {
      switch (e->response_type & ~0x80) {
      case XCB_EXPOSE: {
        char *text;

        text = "Press ESC key to exit...";
        text_draw (c, screen, window, 10, HEIGHT - 10, text);
        break;
      }
      case XCB_KEY_RELEASE: {
        xcb_key_release_event_t *ev;

        ev = (xcb_key_release_event_t *)e;

        switch (ev->detail) {
          /* ESC */
        case 9:
          free (e);
          xcb_disconnect (c);
          return 0;
        }
      }
      }
      free (e);
    }
  }

  return 0;
}

谢谢

Answer 1

Low-level X KeyCodes 位于 8..255 范围内，代表键盘的物理布局。大概在实践中值 9（“1”相对于范围的开始，即 upper-left）是 Esc 键。

话虽如此，hard-code device-specific 这样的知识而不是查找与 Esc KeySym.[=13 相关联的键码似乎是一个非常糟糕的主意=]

这个link似乎提供了一些有用的信息：

https://tronche.com/gui/x/xlib/input/keyboard-encoding.html

Answer 2

I thought I understood it, until I got to "case 9". This was where I got totally lost. So basically, where do they get 9 from? And how does that correspond to ESC?

如果您打开终端运行:

xev | grep keycode

然后你在弹出的xevwindow上按Esc键，你会看到：

    state 0x0, keycode 9 (keysym 0xff1b, Escape), same_screen YES,
    state 0x0, keycode 9 (keysym 0xff1b, Escape), same_screen YES,

你可以做一些疯狂的事情，比如使用 xmodmap 重新映射你的转义键，但它仍然是键码 9，即使你将它映射到其他东西......使用 xmodmap 我将键码 9 重置为F1，但 xev 仍然可以看到我真的在使用 Escape 键（键码 9）

    state 0x0, keycode 9 (keysym 0xffbe, F1), same_screen YES,
    state 0x0, keycode 9 (keysym 0xffbe, F1), same_screen YES,

历史上为什么键码 9 是 Escape 键？

如果你运行:

showkey --ascii
# press the Escape key
^[  27 0033 0x1b

您看到 Escape 映射到 ASCII table 上的 27。同时获取钥匙的“扫描码”：

sudo showkey --scancodes
# press the Escape key
^[  0x01 0x81

由于您在本教程中使用的是 xcb，并且必须考虑的只有 Xcb/X11，因此代码 9 将始终是硬件退出键。

您可以使用 setkeycodes（kbd 包）设置扫描码以映射到 Linux 中的其他键码，但这些代码不会被 X 拾取。

根据您正在操作的层 (USB hardware/kernel/X11)，您需要为适当的密钥选择适当的标识符。

我相信@s0s 所指的教程可在线获取：

https://www.x.org/releases/X11R7.5/doc/libxcb/tutorial/

XCB的事件处理如何检测C中的ESC键？

How does XCB's event handling detect the ESC key in C?

c

events

key

keyrelease

xcb

历史上为什么键码 9 是 Escape 键？