Fix output-specific images when output reappears

When setting an image with `--image <output>:<path>`, the image used to
fail to apply if the relevant output appears some time after swaylock
executes.

Co-authored-by: Alexander Bakker <[email protected]>

include/swaylock.h

@@ -112,6 +112,7 @@ struct swaylock_surface {
 	struct wl_subsurface *subsurface;
 	struct ext_session_lock_surface_v1 *ext_session_lock_surface_v1;
 	struct pool_buffer indicator_buffers[2];
+	bool ready;
 	bool frame_pending, dirty;
 	uint32_t width, height;
 	int32_t scale;

main.c

@@ -124,6 +124,8 @@ static bool surface_is_opaque(struct swaylock_surface *surface) {
 	return (surface->state->args.colors.background & 0xff) == 0xff;
 }
 
+static const struct wl_callback_listener surface_ready_listener;
+
 static void create_surface(struct swaylock_surface *surface) {
 	struct swaylock_state *state = surface->state;
 
@@ -143,6 +145,14 @@ static void create_surface(struct swaylock_surface *surface) {
 	ext_session_lock_surface_v1_add_listener(surface->ext_session_lock_surface_v1,
 		&ext_session_lock_surface_v1_listener, surface);
 
+	// We need to wait for the wl_output.name event to be received before we
+	// can decide which image to display
+	wl_callback_add_listener(
+			wl_display_sync(surface->state->display),
+			&surface_ready_listener, surface);
+}
+
+static void initially_render_surface(struct swaylock_surface *surface) {
 	if (surface_is_opaque(surface) &&
 			surface->state->args.mode != BACKGROUND_MODE_CENTER &&
 			surface->state->args.mode != BACKGROUND_MODE_FIT) {
@@ -152,17 +162,29 @@ static void create_surface(struct swaylock_surface *surface) {
 		wl_surface_set_opaque_region(surface->surface, region);
 		wl_region_destroy(region);
 	}
+
+	render_frame_background(surface);
+	render_frame(surface);
 }
 
+static void handle_surface_ready(void *data, struct wl_callback *callback,
+		uint32_t time) {
+	struct swaylock_surface *surface = (struct swaylock_surface *)data;
+	initially_render_surface(surface);
+	surface->ready = true;
+}
+
+static const struct wl_callback_listener surface_ready_listener = {
+	.done = handle_surface_ready,
+};
+
 static void ext_session_lock_surface_v1_handle_configure(void *data,
 		struct ext_session_lock_surface_v1 *lock_surface, uint32_t serial,
 		uint32_t width, uint32_t height) {
 	struct swaylock_surface *surface = data;
 	surface->width = width;
 	surface->height = height;
 	ext_session_lock_surface_v1_ack_configure(lock_surface, serial);
-	render_frame_background(surface);
-	render_frame(surface);
 }
 
 static const struct ext_session_lock_surface_v1_listener ext_session_lock_surface_v1_listener = {
@@ -250,6 +272,13 @@ static void handle_wl_output_name(void *data, struct wl_output *output,
 		const char *name) {
 	struct swaylock_surface *surface = data;
 	surface->output_name = strdup(name);
+
+	if (surface->output_name != NULL) {
+		cairo_surface_t *new_image = select_image(surface->state, surface);
+		if (new_image != surface->image) {
+			surface->image = new_image;
+		}
+	}
 }
 
 static void handle_wl_output_description(void *data, struct wl_output *output,
@@ -1247,6 +1276,15 @@ int main(int argc, char **argv) {
 		create_surface(surface);
 	}
 
+	wl_list_for_each(surface, &state.surfaces, link) {
+		while (!surface->ready) {
+			if (wl_display_dispatch(state.display) < 0) {
+				swaylock_log(LOG_ERROR, "wl_display_dispatch() failed");
+				return 2;
+			}
+		}
+	}
+
 	while (!state.locked) {
 		if (wl_display_dispatch(state.display) < 0) {
 			swaylock_log(LOG_ERROR, "wl_display_dispatch() failed");