我一直在学习XCB教程，但我被这个教程卡住了。在本例中，当按下ESC键时，程序将退出。但是在示例代码中，我不知道"case 9"是如何捕获ESC键的。我已经搜索并查看了xcb.h和xproto.h以及ASCII表。
我以为我理解了，直到我谈到"案例9"。这就是我完全迷失的地方。所以基本上，他们从哪里得到9？这与ESC有何对应？
以下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 : %dn", 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 : %dn", 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 : %dn", 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 : %dn", 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 : %dn", 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 servern");
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 screenn");
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 : %dn", error->error_code);
xcb_disconnect (c);
return -1;
}
error = xcb_request_check (c, cookie_map);
if (error) {
fprintf (stderr, "ERROR: can't map window : %dn", 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;
}
感谢
低电平XKeyCodes位于8..255范围内，表示键盘的物理布局。在实践中，值9(相对于范围开始的"1"，即左上角)可能是Esc键。
话虽如此，对这样的设备特定知识进行硬编码，而不是查找与EscKeySym相关的密钥代码，似乎是一个非常糟糕的主意。
这个链接似乎提供了一些有用的信息：
https://tronche.com/gui/x/xlib/input/keyboard-encoding.html
我以为我明白了，直到我明白了"情况9"；。这就是我完全迷失的地方。所以基本上，他们从哪里得到9？这与ESC有何对应？
如果您打开一个终端并运行：
xev | grep keycode
然后按下弹出的xev窗口上的Esc键，您将看到：
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来重新映射你的转义密钥，但它仍然是密钥代码9，即使你把它映射到了其他东西。。。使用xmodmap，我将键代码9重置为F1，但xev仍然可以看到我真的在使用Escape键(键代码9)
state 0x0, keycode 9 (keysym 0xffbe, F1), same_screen YES,
state 0x0, keycode 9 (keysym 0xffbe, F1), same_screen YES,
从历史上看，为什么keycode 9是Escape密钥
如果运行：
showkey --ascii
# press the Escape key
^[ 27 0033 0x1b
您可以看到Escape映射到ASCII表上的27。同时抓住钥匙的"；Scancode"：
sudo showkey --scancodes
# press the Escape key
^[ 0x01 0x81
由于您在本教程中使用的是xcb，并且必须只考虑xcb/X11，因此代码9将始终是硬件Escape键。
您可以使用setkeycodes(kbd软件包)设置扫描码以映射到Linux中的其他密钥码，但X 不会拾取这些代码
根据您操作的层(USB硬件/内核/X11)，您需要为相应的密钥选择相应的标识符。
我相信@s0s所指的教程可以在线访问：
https://www.x.org/releases/X11R7.5/doc/libxcb/tutorial/