backend/wayland: maintain a list of active outputs for each virtual WL display

backend/wayland/backend.c

@@ -236,6 +236,13 @@ static const struct zwp_linux_dmabuf_feedback_v1_listener
 	.tranche_flags = linux_dmabuf_feedback_v1_handle_tranche_flags,
 };
 
+static void update_outputs(struct wlr_wl_backend *backend) {
+	struct wlr_wl_output *output;
+	wl_list_for_each(output, &backend->outputs, link) {
+		surface_update(output);
+	}
+}
+
 static void wlr_output_handle_scale(void *data,
 		struct wl_output *wl_output, int32_t factor) {
 	struct wlr_wl_remote_output *output = data;
@@ -254,7 +261,8 @@ static void wlr_output_handle_mode(void *data, struct wl_output *wl_output,
 }
 
 static void wlr_output_handle_done(void *data, struct wl_output *wl_output) {
-	// This is intentionally left blank
+	struct wlr_wl_remote_output *output = data;
+	update_outputs(output->backend);
 }
 
 static const struct wl_output_listener output_listener = {
@@ -436,6 +444,7 @@ static void registry_global(void *data, struct wl_registry *registry,
 		output->output = wl_output;
 		output->scale = 1;
 		output->name = name;
+		output->backend = wl;
 
 		wl_list_insert(&wl->remote_outputs, &output->link);
 		wl_output_add_listener(wl_output, &output_listener, output);

backend/wayland/output.c

@@ -66,6 +66,12 @@ static void presentation_feedback_destroy(
 	free(feedback);
 }
 
+static void active_remote_output_destroy(
+		struct wlr_wl_active_remote_output *output) {
+	wl_list_remove(&output->link);
+	free(output);
+}
+
 static void presentation_feedback_handle_sync_output(void *data,
 		struct wp_presentation_feedback *feedback, struct wl_output *output) {
 	// This space is intentionally left blank
@@ -288,6 +294,12 @@ static bool output_commit(struct wlr_output *wlr_output,
 	}
 
 	if (state->committed & WLR_OUTPUT_STATE_BUFFER) {
+		if (output->requested.needs_ack) {
+			output->requested.needs_ack = false;
+			xdg_surface_ack_configure(output->xdg_surface,
+				output->requested.serial);
+		}
+
 		struct wp_presentation_feedback *wp_feedback = NULL;
 		if (output->backend->presentation != NULL) {
 			wp_feedback = wp_presentation_feedback(output->backend->presentation,
@@ -414,6 +426,12 @@ static void output_destroy(struct wlr_output *wlr_output) {
 		presentation_feedback_destroy(feedback);
 	}
 
+	struct wlr_wl_active_remote_output *active, *active_tmp;
+	wl_list_for_each_safe(active, active_tmp,
+			&output->active_remote_outputs, link) {
+		active_remote_output_destroy(active);
+	}
+
 	if (output->zxdg_toplevel_decoration_v1) {
 		zxdg_toplevel_decoration_v1_destroy(output->zxdg_toplevel_decoration_v1);
 	}
@@ -482,14 +500,41 @@ bool wlr_output_is_wl(struct wlr_output *wlr_output) {
 	return wlr_output->impl == &output_impl;
 }
 
+void surface_update(struct wlr_wl_output *output) {
+	if (wl_list_empty(&output->active_remote_outputs)) {
+		return;
+	}
+
+	struct wlr_output_state state = {
+		.committed = WLR_OUTPUT_STATE_MODE,
+		.mode_type = WLR_OUTPUT_STATE_MODE_CUSTOM,
+		.custom_mode = {
+			.width = output->requested.width,
+			.height = output->requested.height
+		},
+	};
+
+	wlr_output_send_request_state(&output->wlr_output, &state);
+}
+
 static void xdg_surface_handle_configure(void *data,
 		struct xdg_surface *xdg_surface, uint32_t serial) {
 	struct wlr_wl_output *output = data;
 	assert(output && output->xdg_surface == xdg_surface);
 
+	if (wl_list_empty(&output->active_remote_outputs)) {
 		xdg_surface_ack_configure(xdg_surface, serial);
+		wl_surface_commit(output->surface);
+		return;
+	}
 
-	// nothing else?
+	output->requested.needs_ack = true;
+	output->requested.serial = serial;
+	surface_update(output);
+
+	// if the compositor did not commit a new buffer during the surface_update
+	// above, assume that the compositor did not acknowledge the configure.
+	output->requested.needs_ack = false;
 }
 
 static const struct xdg_surface_listener xdg_surface_listener = {
@@ -506,12 +551,8 @@ static void xdg_toplevel_handle_configure(void *data,
 		return;
 	}
 
-	struct wlr_output_state state = {
+	output->requested.width = width;
-		.committed = WLR_OUTPUT_STATE_MODE,
+	output->requested.height = height;
-		.mode_type = WLR_OUTPUT_STATE_MODE_CUSTOM,
-		.custom_mode = { .width = width, .height = height },
-	};
-	wlr_output_send_request_state(&output->wlr_output, &state);
 }
 
 static void xdg_toplevel_handle_close(void *data,
@@ -527,6 +568,50 @@ static const struct xdg_toplevel_listener xdg_toplevel_listener = {
 	.close = xdg_toplevel_handle_close,
 };
 
+static void surface_enter(void *data, struct wl_surface *wl_surface,
+		struct wl_output *wl_output) {
+	struct wlr_wl_output *output = data;
+
+	struct wlr_wl_remote_output *remote_output;
+	wl_list_for_each(remote_output, &output->backend->remote_outputs, link) {
+		if (remote_output->output != wl_output) {
+			continue;
+		}
+
+		struct wlr_wl_active_remote_output *active = calloc(1, sizeof(*active));
+		if (!active) {
+			return;
+		}
+
+		active->remote_output = remote_output;
+
+		wl_list_insert(&output->active_remote_outputs, &active->link);
+		surface_update(output);
+		break;
+	}
+}
+
+static void surface_leave(void *data, struct wl_surface *wl_surface,
+		struct wl_output *wl_output) {
+	struct wlr_wl_output *output = data;
+
+	struct wlr_wl_active_remote_output *active;
+	wl_list_for_each(active, &output->active_remote_outputs, link) {
+		if (active->remote_output->output != wl_output) {
+			continue;
+		}
+
+		active_remote_output_destroy(active);
+		surface_update(output);
+		break;
+	}
+}
+
+static const struct wl_surface_listener surface_listener = {
+	.enter = &surface_enter,
+	.leave = &surface_leave,
+};
+
 struct wlr_output *wlr_wl_output_create(struct wlr_backend *wlr_backend) {
 	struct wlr_wl_backend *backend = get_wl_backend_from_backend(wlr_backend);
 	if (!backend->started) {
@@ -559,6 +644,7 @@ struct wlr_output *wlr_wl_output_create(struct wlr_backend *wlr_backend) {
 
 	output->backend = backend;
 	wl_list_init(&output->presentation_feedbacks);
+	wl_list_init(&output->active_remote_outputs);
 
 	output->surface = wl_compositor_create_surface(backend->compositor);
 	if (!output->surface) {
@@ -598,6 +684,7 @@ struct wlr_output *wlr_wl_output_create(struct wlr_backend *wlr_backend) {
 			&xdg_surface_listener, output);
 	xdg_toplevel_add_listener(output->xdg_toplevel,
 			&xdg_toplevel_listener, output);
+	wl_surface_add_listener(output->surface, &surface_listener, output);
 	wl_surface_commit(output->surface);
 
 	wl_display_roundtrip(output->backend->remote_display);

include/backend/wayland.h

@@ -53,6 +53,7 @@ struct wlr_wl_backend {
 
 struct wlr_wl_remote_output {
 	struct wl_output *output;
+	struct wlr_wl_backend *backend;
 	uint32_t scale;
 
 	// we use this to identify the output in the
@@ -62,6 +63,11 @@ struct wlr_wl_remote_output {
 	struct wl_list link; // wlr_wl_backend.remote_outputs
 };
 
+struct wlr_wl_active_remote_output {
+	struct wlr_wl_remote_output *remote_output;
+	struct wl_list link; // wlr_wl_output.active_remote_outputs
+};
+
 struct wlr_wl_buffer {
 	struct wlr_buffer *buffer;
 	struct wl_buffer *wl_buffer;
@@ -89,9 +95,20 @@ struct wlr_wl_output {
 	struct xdg_toplevel *xdg_toplevel;
 	struct zxdg_toplevel_decoration_v1 *zxdg_toplevel_decoration_v1;
 	struct wl_list presentation_feedbacks;
+	struct wl_list active_remote_outputs; // wlr_wl_active_remote_output.link
 
 	uint32_t enter_serial;
 
+	// last requested output size. This is not the actual size that the
+	// compositor has accepted.
+	struct {
+		bool needs_ack;
+		uint32_t serial;
+
+		int32_t width;
+		int32_t height;
+	} requested;
+
 	struct {
 		struct wlr_wl_pointer *pointer;
 		struct wl_surface *surface;
@@ -167,6 +184,8 @@ bool create_wl_seat(struct wl_seat *wl_seat, struct wlr_wl_backend *wl,
 void destroy_wl_seat(struct wlr_wl_seat *seat);
 void destroy_wl_buffer(struct wlr_wl_buffer *buffer);
 
+void surface_update(struct wlr_wl_output *output);
+
 extern const struct wlr_pointer_impl wl_pointer_impl;
 extern const struct wlr_tablet_pad_impl wl_tablet_pad_impl;
 extern const struct wlr_tablet_impl wl_tablet_impl;