backend/drm: fix hardware cursors not moving

This adds back `wlr_output::needs_swap`. This allows a backend to
request buffer swaps even if the output isn't damaged. This is
needed by the DRM backend to trigger pageflips when the cursor
moves.

backend/drm/drm.c

@@ -619,7 +619,11 @@ static bool wlr_drm_connector_set_cursor(struct wlr_output *output,
 
 	gbm_bo_unmap(bo, bo_data);
 
-	return drm->iface->crtc_set_cursor(drm, crtc, bo);
+	bool ok = drm->iface->crtc_set_cursor(drm, crtc, bo);
+	if (ok) {
+		wlr_output_update_needs_swap(output);
+	}
+	return ok;
 }
 
 static bool wlr_drm_connector_move_cursor(struct wlr_output *output,
@@ -643,8 +647,12 @@ static bool wlr_drm_connector_move_cursor(struct wlr_output *output,
 		transformed_box.y -= plane->cursor_hotspot_y;
 	}
 
-	return drm->iface->crtc_move_cursor(drm, conn->crtc, transformed_box.x,
+	bool ok = drm->iface->crtc_move_cursor(drm, conn->crtc, transformed_box.x,
 		transformed_box.y);
+	if (ok) {
+		wlr_output_update_needs_swap(output);
+	}
+	return ok;
 }
 
 static void wlr_drm_connector_destroy(struct wlr_output *output) {

include/rootston/output.h

@@ -16,11 +16,11 @@ struct roots_output {
 
 	struct timespec last_frame;
 	pixman_region32_t damage, previous_damage;
-	bool frame_scheduled;
+	bool frame_pending;
 
 	struct wl_listener frame;
 	struct wl_listener mode;
-	struct wl_listener damage_listener;
+	struct wl_listener needs_swap;
 };
 
 void output_add_notify(struct wl_listener *listener, void *data);

include/wlr/interfaces/wlr_output.h

@@ -32,5 +32,6 @@ void wlr_output_update_mode(struct wlr_output *output,
 void wlr_output_update_custom_mode(struct wlr_output *output, int32_t width,
 	int32_t height, int32_t refresh);
 void wlr_output_update_enabled(struct wlr_output *output, bool enabled);
+void wlr_output_update_needs_swap(struct wlr_output *output);
 
 #endif

include/wlr/types/wlr_output.h

@@ -54,6 +54,7 @@ struct wlr_output {
 	enum wl_output_subpixel subpixel;
 	enum wl_output_transform transform;
 
+	bool needs_swap;
 	pixman_region32_t damage, previous_damage;
 	float transform_matrix[16];
 
@@ -64,8 +65,8 @@ struct wlr_output {
 	int32_t refresh; // mHz
 
 	struct {
-		struct wl_signal damage;
 		struct wl_signal frame;
+		struct wl_signal needs_swap;
 		struct wl_signal swap_buffers;
 		struct wl_signal enable;
 		struct wl_signal mode;

rootston/output.c

@@ -258,6 +258,7 @@ static void render_output(struct roots_output *output) {
 	struct roots_server *server = desktop->server;
 
 	if (!wlr_output->enabled) {
+		output->frame_pending = false;
 		return;
 	}
 
@@ -299,9 +300,9 @@ static void render_output(struct roots_output *output) {
 	pixman_region32_intersect_rect(&damage, &damage, 0, 0, wlr_output->width,
 		wlr_output->height);
 
-	// TODO: fullscreen
-	if (!pixman_region32_not_empty(&damage)) {
-		output->frame_scheduled = false;
+	if (!pixman_region32_not_empty(&damage) && !wlr_output->needs_swap) {
+		// Output doesn't need swap and isn't damaged, skip rendering completely
+		output->frame_pending = false;
 		goto damage_finish;
 	}
 
@@ -311,6 +312,11 @@ static void render_output(struct roots_output *output) {
 	wlr_renderer_begin(server->renderer, wlr_output);
 	glEnable(GL_SCISSOR_TEST);
 
+	if (!pixman_region32_not_empty(&damage)) {
+		// Output isn't damaged but needs buffer swap
+		goto renderer_end;
+	}
+
 	int nrects;
 	pixman_box32_t *rects = pixman_region32_rectangles(&damage, &nrects);
 	for (int i = 0; i < nrects; ++i) {
@@ -377,7 +383,7 @@ renderer_end:
 	glDisable(GL_SCISSOR_TEST);
 	wlr_renderer_end(server->renderer);
 	wlr_output_swap_buffers(wlr_output, &now, &damage);
-	output->frame_scheduled = true;
+	output->frame_pending = true;
 	pixman_region32_copy(&output->previous_damage, &output->damage);
 	pixman_region32_clear(&output->damage);
 	output->last_frame = desktop->last_frame = now;
@@ -397,11 +403,11 @@ static void handle_idle_render(void *data) {
 }
 
 static void schedule_render(struct roots_output *output) {
-	if (!output->frame_scheduled) {
+	if (!output->frame_pending) {
 		struct wl_event_loop *ev =
 			wl_display_get_event_loop(output->desktop->server->wl_display);
 		wl_event_loop_add_idle(ev, handle_idle_render, output);
-		output->frame_scheduled = true;
+		output->frame_pending = true;
 	}
 }
 
@@ -485,9 +491,9 @@ static void output_handle_mode(struct wl_listener *listener, void *data) {
 	output_damage_whole(output);
 }
 
-static void output_handle_damage(struct wl_listener *listener, void *data) {
+static void output_handle_needs_swap(struct wl_listener *listener, void *data) {
 	struct roots_output *output =
-		wl_container_of(listener, output, damage_listener);
+		wl_container_of(listener, output, needs_swap);
 	pixman_region32_union(&output->damage, &output->damage,
 		&output->wlr_output->damage);
 	schedule_render(output);
@@ -551,8 +557,8 @@ void output_add_notify(struct wl_listener *listener, void *data) {
 	wl_signal_add(&wlr_output->events.frame, &output->frame);
 	output->mode.notify = output_handle_mode;
 	wl_signal_add(&wlr_output->events.mode, &output->mode);
-	output->damage_listener.notify = output_handle_damage;
-	wl_signal_add(&wlr_output->events.damage, &output->damage_listener);
+	output->needs_swap.notify = output_handle_needs_swap;
+	wl_signal_add(&wlr_output->events.needs_swap, &output->needs_swap);
 
 	struct roots_output_config *output_config =
 		roots_config_get_output(config, wlr_output);
@@ -607,5 +613,7 @@ void output_remove_notify(struct wl_listener *listener, void *data) {
 	pixman_region32_fini(&output->previous_damage);
 	wl_list_remove(&output->link);
 	wl_list_remove(&output->frame.link);
+	wl_list_remove(&output->mode.link);
+	wl_list_remove(&output->needs_swap.link);
 	free(output);
 }

types/wlr_output.c

@@ -272,8 +272,8 @@ void wlr_output_init(struct wlr_output *output, struct wlr_backend *backend,
 	output->scale = 1;
 	wl_list_init(&output->cursors);
 	wl_list_init(&output->wl_resources);
-	wl_signal_init(&output->events.damage);
 	wl_signal_init(&output->events.frame);
+	wl_signal_init(&output->events.needs_swap);
 	wl_signal_init(&output->events.swap_buffers);
 	wl_signal_init(&output->events.enable);
 	wl_signal_init(&output->events.mode);
@@ -504,6 +504,7 @@ void wlr_output_swap_buffers(struct wlr_output *output, struct timespec *when,
 
 	// TODO: provide `damage` (not `render_damage`) to backend
 	output->impl->swap_buffers(output);
+	output->needs_swap = false;
 	pixman_region32_copy(&output->previous_damage, &output->damage);
 	pixman_region32_clear(&output->damage);
 
@@ -526,10 +527,15 @@ uint32_t wlr_output_get_gamma_size(struct wlr_output *output) {
 	return output->impl->get_gamma_size(output);
 }
 
+void wlr_output_update_needs_swap(struct wlr_output *output) {
+	output->needs_swap = true;
+	wl_signal_emit(&output->events.needs_swap, output);
+}
+
 static void output_damage_whole(struct wlr_output *output) {
 	pixman_region32_union_rect(&output->damage, &output->damage, 0, 0,
 		output->width, output->height);
-	wl_signal_emit(&output->events.damage, output);
+	wlr_output_update_needs_swap(output);
 }
 
 static void output_fullscreen_surface_reset(struct wlr_output *output) {
@@ -557,7 +563,7 @@ static void output_fullscreen_surface_handle_commit(
 	pixman_region32_union(&output->damage, &output->damage, &damage);
 	pixman_region32_fini(&damage);
 
-	wl_signal_emit(&output->events.damage, output);
+	wlr_output_update_needs_swap(output);
 }
 
 static void output_fullscreen_surface_handle_destroy(
@@ -599,7 +605,7 @@ static void output_cursor_damage_whole(struct wlr_output_cursor *cursor) {
 	output_cursor_get_box(cursor, &box);
 	pixman_region32_union_rect(&cursor->output->damage, &cursor->output->damage,
 		box.x, box.y, box.width, box.height);
-	wl_signal_emit(&cursor->output->events.damage, cursor->output);
+	wlr_output_update_needs_swap(cursor->output);
 }
 
 static void output_cursor_reset(struct wlr_output_cursor *cursor) {