wayland: mucho wip: initial sort-of-working wayland backend

Bar is drawn, though only TOP is supported atm. No
screen/display/output selection is possible yet. Mouse *click* works,
but not setting the cursor.

Lots of debug output, crappy code yada yada.

CMakeLists.txt

@@ -26,11 +26,14 @@ find_package(PkgConfig REQUIRED)
 pkg_check_modules(XCB REQUIRED xcb xcb-aux xcb-cursor xcb-event xcb-ewmh
   xcb-randr xcb-render)
 pkg_check_modules(XCB_ERRORS xcb-errors)
+pkg_check_modules(WAYLAND REQUIRED wayland-client wlroots)
 pkg_check_modules(FONTCONFIG REQUIRED fontconfig)
 pkg_check_modules(CAIRO REQUIRED cairo cairo-xcb cairo-ft)
 pkg_check_modules(YAML REQUIRED yaml-0.1)
 
-add_library(bar-xcb STATIC xcb.c xcb.h bar/xcb.c bar/xcb.h)
+add_library(xcb-stuff STATIC EXCLUDE_FROM_ALL xcb.c xcb.h)
+
+add_library(bar-xcb STATIC EXCLUDE_FROM_ALL bar/xcb.c bar/xcb.h)
 
 target_compile_options(bar-xcb PRIVATE
   ${XCB_CFLAGS_OTHER}
@@ -44,7 +47,49 @@ target_include_directories(bar-xcb PRIVATE
   ${CAIRO_INCLUDE_DIRS}
   )
 
-target_link_libraries(bar-xcb ${XCB_LIBRARIES} ${XCB_ERRORS_LIBRARIES})
+target_link_libraries(bar-xcb xcb-stuff ${XCB_LIBRARIES} ${XCB_ERRORS_LIBRARIES})
+
+add_custom_command(
+  OUTPUT wlr-layer-shell-unstable-v1.c
+  COMMAND wayland-scanner private-code < /home/daniel/AUR/wlroots-git/src/wlroots-git/protocol/wlr-layer-shell-unstable-v1.xml > wlr-layer-shell-unstable-v1.c
+  VERBATIM
+  MAIN_DEPENDENCY /home/daniel/AUR/wlroots-git/src/wlroots-git/protocol/wlr-layer-shell-unstable-v1.xml
+  )
+add_custom_command(
+  OUTPUT wlr-layer-shell-unstable-v1-client.h
+  COMMAND wayland-scanner client-header < /home/daniel/AUR/wlroots-git/src/wlroots-git/protocol/wlr-layer-shell-unstable-v1.xml > wlr-layer-shell-unstable-v1-client.h
+  VERBATIM
+  MAIN_DEPENDENCY /home/daniel/AUR/wlroots-git/src/wlroots-git/protocol/wlr-layer-shell-unstable-v1.xml
+  )
+add_custom_command(
+  OUTPUT xdg-shell.c
+  COMMAND wayland-scanner private-code < /usr/share/wayland-protocols/stable/xdg-shell/xdg-shell.xml > xdg-shell.c
+  VERBATIM
+  MAIN_DEPENDENCY /usr/share/wayland-protocols/stable/xdg-shell/xdg-shell.xml
+  )
+
+add_library(wayland-protocols STATIC EXCLUDE_FROM_ALL
+  wlr-layer-shell-unstable-v1-client.h
+  wlr-layer-shell-unstable-v1.c
+  xdg-shell.c
+  )
+target_include_directories(wayland-protocols PUBLIC ${CMAKE_CURRENT_BINARY_DIR})
+
+add_library(bar-wayland STATIC EXCLUDE_FROM_ALL bar/wayland.c bar/wayland.h)
+target_compile_definitions(bar-wayland PRIVATE _GNU_SOURCE)
+target_compile_options(bar-wayland PRIVATE
+  ${WAYLAND_CFLAGS_OTHER}
+  ${CAIRO_CFLAGS_OTHER}
+  )
+
+target_include_directories(bar-wayland PRIVATE
+  ${CURRENT_BINARY_DIR}
+  ${WAYLAND_INCLUDE_DIRS}
+  ${CAIRO_INCLUDE_DIRS}
+  )
+
+target_link_libraries(bar-wayland wayland-protocols ${WAYLAND_LIBRARIES})
+
 
 add_executable(f00bar
   config.c config.h
@@ -63,7 +108,7 @@ add_executable(f00bar
   bar/bar.c bar/private.h bar/backend.h
   )
 
-target_link_libraries(f00bar bar-xcb)
+target_link_libraries(f00bar xcb-stuff bar-xcb bar-wayland)
 
 # Make global symbols in f00bar visible to dlopen:ed plugins
 set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -rdynamic")

bar/bar.c

@@ -15,6 +15,7 @@
 #include "../log.h"
 
 #include "xcb.h"
+#include "wayland.h"
 
 /*
  * Calculate total width of left/center/rigth groups.
@@ -323,14 +324,17 @@ run(struct bar *_bar)
         m->destroy(m);
     }
 
-    cairo_destroy(bar->cairo);
-    cairo_device_finish(cairo_surface_get_device(bar->cairo_surface));
-    cairo_surface_finish(bar->cairo_surface);
-    cairo_surface_destroy(bar->cairo_surface);
-    cairo_debug_reset_static_data();
-
     bar->backend.iface->cleanup(_bar);
 
+    if (bar->cairo)
+        cairo_destroy(bar->cairo);
+    if (bar->cairo_surface) {
+        cairo_device_finish(cairo_surface_get_device(bar->cairo_surface));
+        cairo_surface_finish(bar->cairo_surface);
+        cairo_surface_destroy(bar->cairo_surface);
+    }
+    cairo_debug_reset_static_data();
+
     LOG_DBG("bar exiting");
     return ret;
 }
@@ -379,8 +383,13 @@ bar_new(const struct bar_config *config)
     //priv->cursor_ctx = NULL;
     //priv->cursor = 0;
     priv->cursor_name = NULL;
+#if 0
     priv->backend.data = bar_backend_xcb_new();
     priv->backend.iface = &xcb_backend_iface;
+#else
+    priv->backend.data = bar_backend_wayland_new();
+    priv->backend.iface = &wayland_backend_iface;
+#endif
 
     for (size_t i = 0; i < priv->left.count; i++) {
         priv->left.mods[i] = config->left.mods[i];

bar/wayland.c

@@ -0,0 +1,587 @@
+#include "wayland.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <unistd.h>
+#include <poll.h>
+
+#include <sys/mman.h>
+#include <linux/memfd.h>
+
+#include <cairo.h>
+#include <wayland-client.h>
+
+#include <wlr-layer-shell-unstable-v1-client.h>
+
+#define LOG_MODULE "bar:wayland"
+#include "../log.h"
+#include "../tllist.h"
+
+#include "private.h"
+
+struct buffer {
+    bool busy;
+    size_t size;
+    void *mmapped;
+
+    struct wl_buffer *wl_buf;
+
+    cairo_surface_t *cairo_surface;
+    cairo_t *cairo;
+};
+
+struct wayland_backend {
+    struct wl_display *display;
+    struct wl_registry *registry;
+    struct wl_compositor *compositor;
+    struct wl_output *output;
+    struct wl_surface *surface;
+    struct zwlr_layer_shell_v1 *layer_shell;
+    struct zwlr_layer_surface_v1 *layer_surface;
+    struct wl_shm *shm;
+    struct wl_seat *seat;
+
+    struct {
+        struct wl_pointer *pointer;
+        int x;
+        int y;
+    } pointer;
+
+    /* TODO: set directly in bar instead */
+    int width, height;
+
+    /* Used to signal e.g. refresh */
+    int pipe_fds[2];
+
+    /* We're already waiting for a frame done callback */
+    bool render_scheduled;
+
+    tll(struct buffer) buffers;     /* List of SHM buffers */
+    struct buffer *next_buffer;     /* Bar is rendering to this one */
+    struct buffer *pending_buffer;  /* Finished, but not yet rendered */
+};
+
+void *
+bar_backend_wayland_new(void)
+{
+    return calloc(1, sizeof(struct wayland_backend));
+}
+
+static void
+shm_format(void *data, struct wl_shm *wl_shm, uint32_t format)
+{
+    printf("SHM format: 0x%08x\n", format);
+}
+
+static const struct wl_shm_listener shm_listener = {
+    .format = &shm_format,
+};
+
+static void
+wl_pointer_enter(void *data, struct wl_pointer *wl_pointer,
+                 uint32_t serial, struct wl_surface *surface,
+                 wl_fixed_t surface_x, wl_fixed_t surface_y)
+{
+}
+
+static void
+wl_pointer_leave(void *data, struct wl_pointer *wl_pointer,
+                 uint32_t serial, struct wl_surface *surface)
+{
+}
+
+static void
+wl_pointer_motion(void *data, struct wl_pointer *wl_pointer,
+                  uint32_t time, wl_fixed_t surface_x, wl_fixed_t surface_y)
+{
+    struct wayland_backend *backend = data;
+    printf("MOTION: %dx%d\n", wl_fixed_to_int(surface_x), wl_fixed_to_int(surface_y));
+    backend->pointer.x = wl_fixed_to_int(surface_x);
+    backend->pointer.y = wl_fixed_to_int(surface_y);
+}
+
+static void
+wl_pointer_button(void *data, struct wl_pointer *wl_pointer,
+                  uint32_t serial, uint32_t time, uint32_t button, uint32_t state)
+{
+    if (state != WL_POINTER_BUTTON_STATE_PRESSED)
+        return;
+
+    struct wayland_backend *backend = data;
+    printf("BUTTON: %dx%d\n", backend->pointer.x, backend->pointer.y);
+
+    write(backend->pipe_fds[1], &(uint8_t){2}, sizeof(uint8_t));
+    write(backend->pipe_fds[1], &backend->pointer.x, sizeof(backend->pointer.x));
+    write(backend->pipe_fds[1], &backend->pointer.y, sizeof(backend->pointer.y));
+}
+
+static void
+wl_pointer_axis(void *data, struct wl_pointer *wl_pointer,
+                uint32_t time, uint32_t axis, wl_fixed_t value)
+{
+}
+
+static void
+wl_pointer_frame(void *data, struct wl_pointer *wl_pointer)
+{
+}
+
+static void
+wl_pointer_axis_source(void *data, struct wl_pointer *wl_pointer,
+                       uint32_t axis_source)
+{
+}
+
+static void
+wl_pointer_axis_stop(void *data, struct wl_pointer *wl_pointer,
+                     uint32_t time, uint32_t axis)
+{
+}
+
+static void
+wl_pointer_axis_discrete(void *data, struct wl_pointer *wl_pointer,
+                         uint32_t axis, int32_t discrete)
+{
+}
+
+static const struct wl_pointer_listener pointer_listener = {
+    .enter = wl_pointer_enter,
+    .leave = wl_pointer_leave,
+    .motion = wl_pointer_motion,
+    .button = wl_pointer_button,
+    .axis = wl_pointer_axis,
+    .frame = wl_pointer_frame,
+    .axis_source = wl_pointer_axis_source,
+    .axis_stop = wl_pointer_axis_stop,
+    .axis_discrete = wl_pointer_axis_discrete,
+};
+
+static void
+seat_handle_capabilities(void *data, struct wl_seat *wl_seat,
+                         enum wl_seat_capability caps)
+{
+    struct wayland_backend *backend = data;
+
+    if (backend->pointer.pointer != NULL) {
+        wl_pointer_release(backend->pointer.pointer);
+        backend->pointer.pointer = NULL;
+    }
+
+    if ((caps & WL_SEAT_CAPABILITY_POINTER)) {
+        backend->pointer.pointer = wl_seat_get_pointer(wl_seat);
+        wl_pointer_add_listener(backend->pointer.pointer, &pointer_listener, backend);
+    }
+}
+
+static void
+seat_handle_name(void *data, struct wl_seat *wl_seat, const char *name)
+{
+    printf("seat: name=%s\n", name);
+}
+
+static const struct wl_seat_listener seat_listener = {
+    .capabilities = seat_handle_capabilities,
+    .name = seat_handle_name,
+};
+
+static void
+handle_global(void *data, struct wl_registry *registry,
+              uint32_t name, const char *interface, uint32_t version)
+{
+    struct wayland_backend *backend = data;
+    if (strcmp(interface, wl_compositor_interface.name) == 0) {
+        backend->compositor = wl_registry_bind(
+            registry, name, &wl_compositor_interface, 4);
+    }
+
+    else if (strcmp(interface, wl_shm_interface.name) == 0) {
+        backend->shm = wl_registry_bind(registry, name, &wl_shm_interface, 1);
+        wl_shm_add_listener(backend->shm, &shm_listener, backend);
+    }
+
+    else if (strcmp(interface, wl_output_interface.name) == 0) {
+        backend->output = wl_registry_bind(registry, name, &wl_output_interface, 3);
+        //output_add_listener(backend->output, &output_listener, backend);
+    }
+
+    else if (strcmp(interface, zwlr_layer_shell_v1_interface.name) == 0) {
+        backend->layer_shell = wl_registry_bind(
+            registry, name, &zwlr_layer_shell_v1_interface, 1);
+    }
+
+    else if (strcmp(interface, wl_seat_interface.name) == 0) {
+        backend->seat = wl_registry_bind(registry, name, &wl_seat_interface, 3);
+        wl_seat_add_listener(backend->seat, &seat_listener, backend);
+    }
+}
+
+static void
+handle_global_remove(void *data, struct wl_registry *registry, uint32_t name)
+{
+    //struct wayland_backend *backend = data;
+}
+
+static const struct wl_registry_listener registry_listener = {
+    .global = &handle_global,
+    .global_remove = &handle_global_remove,
+};
+
+static void
+layer_surface_configure(void *data, struct zwlr_layer_surface_v1 *surface,
+                        uint32_t serial, uint32_t w, uint32_t h)
+{
+    struct wayland_backend *backend = data;
+    backend->width = w;
+    backend->height = h;
+
+    zwlr_layer_surface_v1_ack_configure(surface, serial);
+}
+
+static const struct zwlr_layer_surface_v1_listener layer_surface_listener = {
+    .configure = layer_surface_configure,
+};
+
+static void
+buffer_release(void *data, struct wl_buffer *wl_buffer)
+{
+    printf("buffer release\n");
+    struct buffer *buffer = data;
+    assert(buffer->busy);
+    buffer->busy = false;
+}
+
+static const struct wl_buffer_listener buffer_listener = {
+    .release = &buffer_release,
+};
+
+static struct buffer *
+get_buffer(struct wayland_backend *backend)
+{
+    tll_foreach(backend->buffers, it) {
+        if (!it->item.busy) {
+            printf("re-using non-busy buffer\n");
+            it->item.busy = true;
+            return &it->item;
+        }
+    }
+
+    printf("allocating a new buffer\n");
+
+    struct buffer buffer;
+
+    /* Backing memory for SHM */
+    int pool_fd = memfd_create("wayland-test-buffer-pool", MFD_CLOEXEC);
+    assert(pool_fd != -1);
+
+    /* Allocate memory for our single buffer */
+    uint32_t stride = backend->width * 4;
+    buffer.size = stride * backend->height;
+    ftruncate(pool_fd, buffer.size);
+
+    buffer.mmapped = mmap(
+        NULL, buffer.size, PROT_READ | PROT_WRITE, MAP_SHARED, pool_fd, 0);
+    assert(buffer.mmapped != MAP_FAILED);
+
+    struct wl_shm_pool *pool = wl_shm_create_pool(backend->shm, pool_fd, buffer.size);
+    assert(pool != NULL);
+
+    buffer.wl_buf = wl_shm_pool_create_buffer(
+        pool, 0, backend->width, backend->height, stride, WL_SHM_FORMAT_ARGB8888);
+    assert(buffer.wl_buf != NULL);
+    buffer.busy = true;
+
+    wl_shm_pool_destroy(pool);
+    close(pool_fd);
+
+    buffer.cairo_surface = cairo_image_surface_create_for_data(
+        buffer.mmapped, CAIRO_FORMAT_ARGB32, backend->width, backend->height, stride);
+    buffer.cairo = cairo_create(buffer.cairo_surface);
+    assert(cairo_status(buffer.cairo) == CAIRO_STATUS_SUCCESS);
+
+    tll_push_back(backend->buffers, buffer);
+
+    struct buffer *ret = &tll_back(backend->buffers);
+    wl_buffer_add_listener(buffer.wl_buf, &buffer_listener, ret);
+    return ret;
+}
+
+static bool
+setup(struct bar *_bar)
+{
+    struct private *bar = _bar->private;
+    struct wayland_backend *backend = bar->backend.data;
+
+    backend->display = wl_display_connect(NULL);
+    assert(backend->display != NULL);
+
+    backend->registry = wl_display_get_registry(backend->display);
+    assert(backend->registry != NULL);
+
+    wl_registry_add_listener(backend->registry, &registry_listener, backend);
+
+    wl_display_roundtrip(backend->display);
+    assert(backend->compositor != NULL &&
+           backend->layer_shell != NULL &&
+           backend->output != NULL);
+
+    backend->surface = wl_compositor_create_surface(backend->compositor);
+    assert(backend->surface != NULL);
+
+    backend->layer_surface = zwlr_layer_shell_v1_get_layer_surface(
+        backend->layer_shell, backend->surface, backend->output,
+        ZWLR_LAYER_SHELL_V1_LAYER_BOTTOM, "f00bar");
+    assert(backend->layer_surface != NULL);
+
+    /* Aligned to top, maximum width */
+    zwlr_layer_surface_v1_set_anchor(
+        backend->layer_surface,
+        ZWLR_LAYER_SURFACE_V1_ANCHOR_LEFT |
+        ZWLR_LAYER_SURFACE_V1_ANCHOR_RIGHT |
+        ZWLR_LAYER_SURFACE_V1_ANCHOR_TOP);
+
+    zwlr_layer_surface_v1_set_size(backend->layer_surface, 0, bar->height_with_border);
+    zwlr_layer_surface_v1_set_exclusive_zone(backend->layer_surface, bar->height_with_border);
+
+    //zwlr_layer_surface_v1_set_margin(
+    //   layer_surface, margin_top, margin_right, margin_bottom, margin_left);
+    //zwlr_layer_surface_v1_set_keyboard_interactivity(
+    //   layer_surface, keyboard_interactive);
+
+    zwlr_layer_surface_v1_add_listener(
+        backend->layer_surface, &layer_surface_listener, backend);
+
+    /* Assign width/height */
+    wl_surface_commit(backend->surface);
+    wl_display_roundtrip(backend->display);
+
+    assert(backend->width != -1 && backend->height == bar->height_with_border);
+    bar->width = backend->width;
+
+    pipe(backend->pipe_fds);
+    backend->render_scheduled = false;
+
+    wl_surface_commit(backend->surface);
+    wl_display_roundtrip(backend->display);
+
+    backend->next_buffer = get_buffer(backend);
+    assert(backend->next_buffer != NULL && backend->next_buffer->busy);
+
+    bar->cairo_surface = backend->next_buffer->cairo_surface;
+    bar->cairo = backend->next_buffer->cairo;
+
+    return true;
+}
+
+static void
+cleanup(struct bar *_bar)
+{
+    struct private *bar = _bar->private;
+    struct wayland_backend *backend = bar->backend.data;
+
+    tll_foreach(backend->buffers, it) {
+        wl_buffer_destroy(it->item.wl_buf);
+        cairo_destroy(it->item.cairo);
+        cairo_surface_destroy(it->item.cairo_surface);
+        munmap(it->item.mmapped, it->item.size);
+
+        tll_remove(backend->buffers, it);
+    }
+
+    /* TODO: move to bar */
+    free(bar->cursor_name);
+
+    zwlr_layer_surface_v1_destroy(backend->layer_surface);
+    zwlr_layer_shell_v1_destroy(backend->layer_shell);
+    wl_compositor_destroy(backend->compositor);
+    wl_surface_destroy(backend->surface);
+    wl_shm_destroy(backend->shm);
+    wl_output_destroy(backend->output);
+    wl_registry_destroy(backend->registry);
+    wl_display_disconnect(backend->display);
+
+    /* Destroyed when freeing buffer list */
+    bar->cairo_surface = NULL;
+    bar->cairo = NULL;
+
+}
+
+static void
+loop(struct bar *_bar,
+     void (*expose)(const struct bar *bar),
+     void (*on_mouse)(struct bar *bar, enum mouse_event event, int x, int y))
+{
+    struct private *bar = _bar->private;
+    struct wayland_backend *backend = bar->backend.data;
+
+#if 0
+    while (wl_display_prepare_read(backend->display) != 0){
+        printf("initial wayland event\n");
+        wl_display_dispatch_pending(backend->display);
+    }
+    wl_display_flush(backend->display);
+#endif
+
+    wl_display_dispatch_pending(backend->display);
+    wl_display_flush(backend->display);
+
+    while (true) {
+        struct pollfd fds[] = {
+            {.fd = _bar->abort_fd, .events = POLLIN},
+            {.fd = wl_display_get_fd(backend->display), .events = POLLIN},
+            {.fd = backend->pipe_fds[0], .events = POLLIN},
+        };
+
+        wl_display_flush(backend->display);
+
+        printf("polling\n");
+        poll(fds, sizeof(fds) / sizeof(fds[0]), -1);
+        if (fds[0].revents & POLLIN) {
+            //wl_display_cancel_read(backend->display);
+            break;
+        }
+
+        if (fds[1].revents & POLLHUP) {
+            LOG_WARN("disconnceted from wayland");
+            write(_bar->abort_fd, &(uint64_t){1}, sizeof(uint64_t));
+            break;
+        }
+
+        if (fds[2].revents & POLLIN) {
+            uint8_t command;
+            //wl_display_cancel_read(backend->display);
+            read(backend->pipe_fds[0], &command, sizeof(command));
+
+            if (command == 1) {
+                printf("refresh\n");
+                assert(command == 1);
+                expose(_bar);
+#if 0
+                while (wl_display_prepare_read(backend->display) != 0) {
+                    printf("queued wayland events\n");
+                    wl_display_dispatch_pending(backend->display);
+                }
+                wl_display_flush(backend->display);
+#endif
+            }
+
+            if (command == 2) {
+                printf("mouse\n");
+                int x, y;
+                read(backend->pipe_fds[0], &x, sizeof(x));
+                read(backend->pipe_fds[0], &y, sizeof(y));
+                on_mouse(_bar, ON_MOUSE_CLICK, x, y);
+            }
+            continue;
+        }
+
+#if 0
+        printf("wayland events\n");
+        wl_display_read_events(backend->display);
+        wl_display_dispatch_pending(backend->display);
+#endif
+        printf("wayland events\n");
+        wl_display_dispatch(backend->display);
+    }
+}
+
+static void frame_callback(
+    void *data, struct wl_callback *wl_callback, uint32_t callback_data);
+
+static const struct wl_callback_listener frame_listener = {
+    .done = &frame_callback,
+};
+
+static void
+frame_callback(void *data, struct wl_callback *wl_callback, uint32_t callback_data)
+{
+    printf("frame callback\n");
+    struct private *bar = data;
+    struct wayland_backend *backend = bar->backend.data;
+
+    backend->render_scheduled = false;
+
+    wl_callback_destroy(wl_callback);
+
+    if (backend->pending_buffer != NULL) {
+        struct buffer *buffer = backend->pending_buffer;
+        assert(buffer->busy);
+
+        wl_surface_attach(backend->surface, buffer->wl_buf, 0, 0);
+        wl_surface_damage(backend->surface, 0, 0, backend->width, backend->height);
+
+        struct wl_callback *cb = wl_surface_frame(backend->surface);
+        wl_callback_add_listener(cb, &frame_listener, bar);
+        wl_surface_commit(backend->surface);
+
+        backend->pending_buffer = NULL;
+        backend->render_scheduled = true;
+    } else
+        printf("nothing more to do\n");
+}
+
+static void
+commit_surface(const struct bar *_bar)
+{
+    struct private *bar = _bar->private;
+    struct wayland_backend *backend = bar->backend.data;
+
+    printf("commit: %dxl%d\n", backend->width, backend->height);
+
+    assert(backend->next_buffer != NULL);
+    assert(backend->next_buffer->busy);
+
+    if (backend->render_scheduled) {
+        printf("already scheduled\n");
+
+        if (backend->pending_buffer != NULL)
+            backend->pending_buffer->busy = false;
+
+        backend->pending_buffer = backend->next_buffer;
+        backend->next_buffer = NULL;
+    } else {
+
+        printf("scheduling new frame callback\n");
+        struct buffer *buffer = backend->next_buffer;
+        assert(buffer->busy);
+
+        wl_surface_attach(backend->surface, buffer->wl_buf, 0, 0);
+        wl_surface_damage(backend->surface, 0, 0, backend->width, backend->height);
+
+        struct wl_callback *cb = wl_surface_frame(backend->surface);
+        wl_callback_add_listener(cb, &frame_listener, bar);
+        wl_surface_commit(backend->surface);
+
+        backend->render_scheduled = true;
+    }
+
+    backend->next_buffer = get_buffer(backend);
+    assert(backend->next_buffer != NULL && backend->next_buffer->busy);
+
+    bar->cairo_surface = backend->next_buffer->cairo_surface;
+    bar->cairo = backend->next_buffer->cairo;
+}
+
+static void
+refresh(const struct bar *_bar)
+{
+    const struct private *bar = _bar->private;
+    const struct wayland_backend *backend = bar->backend.data;
+
+    write(backend->pipe_fds[1], &(uint8_t){1}, sizeof(uint8_t));
+}
+
+static void
+set_cursor(struct bar *_bar, const char *cursor)
+{
+}
+
+const struct backend wayland_backend_iface = {
+    .setup = &setup,
+    .cleanup = &cleanup,
+    .loop = &loop,
+    .commit_surface = &commit_surface,
+    .refresh = &refresh,
+    .set_cursor = &set_cursor,
+};

bar/wayland.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include "backend.h"
+
+extern const struct backend wayland_backend_iface;
+
+void *bar_backend_wayland_new(void);

main.c

@@ -46,7 +46,7 @@ get_config_path(void)
         path_max = 1024;
 
     char *path = malloc(path_max + 1);
-    snprintf(path, path_max + 1, "%s/.config/f00bar/config.yml", home_dir);
+    snprintf(path, path_max + 1, "%s/.config/f00bar/config-wayland.yml", home_dir);
     return path;
 }