扩展示例代码
利用我们目前为止所学到的知识，我们现在可以写一个 Wayland 客户端，以在屏幕上显示一些东西。下面的代码是一个完整的 Wayland 应用程序，它可以打开一个 XDG 顶层窗口，并在上面显示一个 640x480 像素的棋盘格。
可以像这样编译它：
wayland-scanner private-code \
< /usr/share/wayland-protocols/stable/xdg-shell/xdg-shell.xml \
> xdg-shell-protocol.c
wayland-scanner client-header \
< /usr/share/wayland-protocols/stable/xdg-shell/xdg-shell.xml \
> xdg-shell-client-protocol.h
cc -o client client.c xdg-shell-protocol.c -lwayland-client -lrt
然后运行 ./client 来查看其情况，或者运行 WAYLAND_DEBUG=1 ./client 来包含更多有用的调试信息。在未来的章节中，我们将在这个客户端的基础上进行开发，所以要将这些代码妥善保管。
#define _POSIX_C_SOURCE 200112L
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdbool.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include <wayland-client.h>
#include "xdg-shell-client-protocol.h"
/* Shared memory support code */
static void
randname(char *buf)
{
// 返回一个随机的名字
struct timespec ts;
clock_gettime(CLOCK_REALTIME, &ts);
long r = ts.tv_nsec;
for (int i = 0; i < 6; ++i) {
buf[i] = 'A'+(r&15)+(r&16)*2;
r >>= 5;
}
}
static int
create_shm_file(void)
{
int retries = 100;
do {
char name[] = "/wl_shm-XXXXXX";
randname(name + sizeof(name) - 7);
--retries;
int fd = shm_open(name, O_RDWR | O_CREAT | O_EXCL, 0600);
if (fd >= 0) {
shm_unlink(name);
return fd;
}
} while (retries > 0 && errno == EEXIST);
return -1;
}
static int
allocate_shm_file(size_t size)
{
int fd = create_shm_file();
if (fd < 0)
return -1;
int ret;
do {
/*
* 关于 ftruncate 的内容可以参考
* https://www.man7.org/linux/man-pages/man3/ftruncate.3p.html
*/
ret = ftruncate(fd, size);
} while (ret < 0 && errno == EINTR);
if (ret < 0) {
close(fd);
return -1;
}
return fd;
}
/* Wayland code */
struct client_state {
/* Globals */
struct wl_display *wl_display;
struct wl_registry *wl_registry;
struct wl_shm *wl_shm;
struct wl_compositor *wl_compositor;
struct xdg_wm_base *xdg_wm_base;
/* Objects */
struct wl_surface *wl_surface;
struct xdg_surface *xdg_surface;
struct xdg_toplevel *xdg_toplevel;
};
static void
wl_buffer_release(void *data, struct wl_buffer *wl_buffer)
{
/* Sent by the compositor when it's no longer using this buffer */
wl_buffer_destroy(wl_buffer);
}
static const struct wl_buffer_listener wl_buffer_listener = {
.release = wl_buffer_release,
};
static struct wl_buffer *
draw_frame(struct client_state *state)
{
const int width = 640, height = 480;
int stride = width * 4;
int size = stride * height;
int fd = allocate_shm_file(size);
if (fd == -1) {
return NULL;
}
uint32_t *data = mmap(NULL, size,
PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (data == MAP_FAILED) {
close(fd);
return NULL;
}
// 创建一个共享内存池
struct wl_shm_pool *pool = wl_shm_create_pool(state->wl_shm, fd, size);
// 创建一个缓冲区
struct wl_buffer *buffer = wl_shm_pool_create_buffer(pool, 0,
width, height, stride, WL_SHM_FORMAT_XRGB8888);
wl_shm_pool_destroy(pool);
close(fd);
/* Draw checkerboxed background */
for (int y = 0; y < height; ++y) {
for (int x = 0; x < width; ++x) {
if ((x + y / 8 * 8) % 16 < 8)
data[y * width + x] = 0xFF666666;
else
data[y * width + x] = 0xFFEEEEEE;
}
}
munmap(data, size);
// 添加监听器用于检测释放缓冲区的事件
wl_buffer_add_listener(buffer, &wl_buffer_listener, NULL);
return buffer;
}
static void
xdg_surface_configure(void *data,
struct xdg_surface *xdg_surface, uint32_t serial)
{
struct client_state *state = data;
// 返回一个 ack_configure 以示确认
xdg_surface_ack_configure(xdg_surface, serial);
// 向缓冲区中绘制内容
struct wl_buffer *buffer = draw_frame(state);
// 将缓冲区内容附加到表面
wl_surface_attach(state->wl_surface, buffer, 0, 0);
// 提交表面
wl_surface_commit(state->wl_surface);
}
static const struct xdg_surface_listener xdg_surface_listener = {
.configure = xdg_surface_configure,
};
static void
xdg_wm_base_ping(void *data, struct xdg_wm_base *xdg_wm_base, uint32_t serial)
{
xdg_wm_base_pong(xdg_wm_base, serial);
}
static const struct xdg_wm_base_listener xdg_wm_base_listener = {
.ping = xdg_wm_base_ping,
};
static void
registry_global(void *data, struct wl_registry *wl_registry,
uint32_t name, const char *interface, uint32_t version)
{
struct client_state *state = data;
// 绑定到全局
if (strcmp(interface, wl_shm_interface.name) == 0) {
state->wl_shm = wl_registry_bind(
wl_registry, name, &wl_shm_interface, 1);
} else if (strcmp(interface, wl_compositor_interface.name) == 0) {
state->wl_compositor = wl_registry_bind(
wl_registry, name, &wl_compositor_interface, 4);
} else if (strcmp(interface, xdg_wm_base_interface.name) == 0) {
state->xdg_wm_base = wl_registry_bind(
wl_registry, name, &xdg_wm_base_interface, 1);
xdg_wm_base_add_listener(state->xdg_wm_base,
&xdg_wm_base_listener, state);
}
}
static void
registry_global_remove(void *data,
struct wl_registry *wl_registry, uint32_t name)
{
/* This space deliberately left blank */
}
static const struct wl_registry_listener wl_registry_listener = {
.global = registry_global,
.global_remove = registry_global_remove,
};
int
main(int argc, char *argv[])
{
// 初始化状态
struct client_state state = { 0 };
// 获取默认显示器
state.wl_display = wl_display_connect(NULL);
// 注册到默认显示器
state.wl_registry = wl_display_get_registry(state.wl_display);
// 添加事件监听
wl_registry_add_listener(state.wl_registry, &wl_registry_listener, &state);
// 以 wl_display 作为代理连接到混成器
wl_display_roundtrip(state.wl_display);
// 从混成器创建一个表面
state.wl_surface = wl_compositor_create_surface(state.wl_compositor);
// 从 wl_surface 创建一个 xdg_surface
state.xdg_surface = xdg_wm_base_get_xdg_surface(
state.xdg_wm_base, state.wl_surface);
// 添加事件监听
xdg_surface_add_listener(state.xdg_surface, &xdg_surface_listener, &state);
// 获得顶层窗口
state.xdg_toplevel = xdg_surface_get_toplevel(state.xdg_surface);
// 设置标题
xdg_toplevel_set_title(state.xdg_toplevel, "Example client");
// 提交表面
wl_surface_commit(state.wl_surface);
while (wl_display_dispatch(state.wl_display)) {
/* This space deliberately left blank */
}
return 0;
}