frame.cpp

#include <cerrno>
#include <fcntl.h>
#include <cstring>
#include <sys/mman.h>
#include <ctime>
#include <unistd.h>
#include <wayland-client.h>
#include "xdg-shell-client-protocol.h"

/* Shared memory support code */
static void randname(char *buf) {
    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() {
    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 {
        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;

    float offset;
    uint32_t last_frame;
};

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 nullptr;
    }

    uint32_t *data = static_cast<uint32_t *>(mmap(NULL, size,
                                                  PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0));
    if (data == MAP_FAILED) {
        close(fd);
        return NULL;
    }

    struct wl_shm_pool *pool = wl_shm_create_pool(state->wl_shm, fd, size);
    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 */
    int offset = (int)state->offset%8;
    for (int y = 0; y < height; ++y) {
        for (int x = 0; x < width; ++x) {
            if (((x + offset) + (y + offset) / 8 * 8) % 16 < 8)
                data[y * width + x] = 0xFF666666;
            else
                data[y * width + x] = 0xFFEEEEEE;
        }
    }

    munmap(data, size);
    wl_buffer_add_listener(buffer, &wl_buffer_listener, NULL);
    return buffer;
}

static void
wl_surface_frame_done(void *data, struct wl_callback *cb, uint32_t time);

static const struct wl_callback_listener wl_surface_frame_listener = {
        .done = wl_surface_frame_done,
        };

static void xdg_surface_configure(void *data,
                                  struct xdg_surface *xdg_surface, uint32_t serial) {
    struct client_state *state = static_cast<client_state *>(data);
    xdg_surface_ack_configure(xdg_surface, serial);


    struct wl_buffer *buffer = draw_frame(state);
    wl_surface_attach(state->wl_surface, buffer, 0, 0);
    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
wl_surface_frame_done(void *data, struct wl_callback *cb, uint32_t time) {
    /* Destroy this callback */
    wl_callback_destroy(cb);

    /* Request another frame */
    struct client_state *state = static_cast<client_state *>(data);
    cb = wl_surface_frame(state->wl_surface);
    wl_callback_add_listener(cb, &wl_surface_frame_listener, state);

    /* Update scroll amount at 24 pixels per second */
    if (state->last_frame != 0) {
        int elapsed = time - state->last_frame;
        state->offset += elapsed / 1000.0 * 24;
    }

    /* Submit a frame for this event */
    struct wl_buffer *buffer = draw_frame(state);
    wl_surface_attach(state->wl_surface, buffer, 0, 0);
    wl_surface_damage_buffer(state->wl_surface, 0, 0, INT32_MAX, INT32_MAX);
    wl_surface_commit(state->wl_surface);

    state->last_frame = time;
}

static void registry_global(void *data, struct wl_registry *wl_registry,
        uint32_t name, const char *interface, uint32_t version) {
    struct client_state *state = static_cast<client_state *>(data);
    if (strcmp(interface, wl_shm_interface.name) == 0) {
        state->wl_shm = static_cast<wl_shm *>(wl_registry_bind(
                wl_registry, name, &wl_shm_interface, 1));
    } else if (strcmp(interface, wl_compositor_interface.name) == 0) {
        state->wl_compositor = static_cast<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 = static_cast<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[]) {
    struct client_state state = {0};
    state.wl_display = wl_display_connect(NULL);
    state.wl_registry = wl_display_get_registry(state.wl_display);
    wl_registry_add_listener(state.wl_registry, &wl_registry_listener, &state);
    wl_display_roundtrip(state.wl_display);

    state.wl_surface = wl_compositor_create_surface(state.wl_compositor);
    state.xdg_surface = xdg_wm_base_get_xdg_surface(
            state.xdg_wm_base, state.wl_surface);
    xdg_surface_add_listener(state.xdg_surface, &xdg_surface_listener, &state);
    state.xdg_toplevel = xdg_surface_get_toplevel(state.xdg_surface);
    xdg_toplevel_set_title(state.xdg_toplevel, "Example client");
    wl_surface_commit(state.wl_surface);

    struct wl_callback *cb = wl_surface_frame(state.wl_surface);
    wl_callback_add_listener(cb, &wl_surface_frame_listener, &state);

    while (wl_display_dispatch(state.wl_display)) {
        /* This space deliberately left blank */
    }

    return 0;
}