backend/drm: add libliftoff composition layer

This will be useful for implementing the output layers API.

backend/drm/libliftoff.c

@@ -45,6 +45,14 @@ static bool init(struct wlr_drm_backend *drm) {
 			return false;
 		}
 
+		crtc->liftoff_composition_layer = liftoff_layer_create(crtc->liftoff);
+		if (!crtc->liftoff_composition_layer) {
+			wlr_log(WLR_ERROR, "Failed to create liftoff composition layer");
+			return false;
+		}
+		liftoff_output_set_composition_layer(crtc->liftoff,
+			crtc->liftoff_composition_layer);
+
 		if (crtc->primary) {
 			crtc->primary->liftoff_layer = liftoff_layer_create(crtc->liftoff);
 			if (!crtc->primary->liftoff_layer) {
@@ -96,6 +104,7 @@ static void finish(struct wlr_drm_backend *drm) {
 			liftoff_layer_destroy(crtc->cursor->liftoff_layer);
 		}
 
+		liftoff_layer_destroy(crtc->liftoff_composition_layer);
 		liftoff_output_destroy(crtc->liftoff);
 	}
 
@@ -133,7 +142,7 @@ static void rollback_blob(struct wlr_drm_backend *drm,
 }
 
 static bool set_plane_props(struct wlr_drm_plane *plane,
-		int32_t x, int32_t y, uint64_t zpos) {
+		struct liftoff_layer *layer, int32_t x, int32_t y, uint64_t zpos) {
 	struct wlr_drm_fb *fb = plane_get_next_fb(plane);
 	if (fb == NULL) {
 		wlr_log(WLR_ERROR, "Failed to acquire FB");
@@ -144,7 +153,6 @@ static bool set_plane_props(struct wlr_drm_plane *plane,
 	uint32_t height = fb->wlr_buf->height;
 
 	// The SRC_* properties are in 16.16 fixed point
-	struct liftoff_layer *layer = plane->liftoff_layer;
 	return liftoff_layer_set_property(layer, "zpos", zpos) == 0 &&
 		liftoff_layer_set_property(layer, "SRC_X", 0) == 0 &&
 		liftoff_layer_set_property(layer, "SRC_Y", 0) == 0 &&
@@ -263,12 +271,16 @@ static bool crtc_commit(struct wlr_drm_connector *conn,
 		if (crtc->props.vrr_enabled != 0) {
 			ok = ok && add_prop(req, crtc->id, crtc->props.vrr_enabled, vrr_enabled);
 		}
-		ok = ok && set_plane_props(crtc->primary, 0, 0, 0);
+		ok = ok &&
+			set_plane_props(crtc->primary, crtc->primary->liftoff_layer, 0, 0, 0) &&
+			set_plane_props(crtc->primary, crtc->liftoff_composition_layer, 0, 0, 0);
 		liftoff_layer_set_property(crtc->primary->liftoff_layer,
 			"FB_DAMAGE_CLIPS", fb_damage_clips);
+		liftoff_layer_set_property(crtc->liftoff_composition_layer,
+			"FB_DAMAGE_CLIPS", fb_damage_clips);
 		if (crtc->cursor) {
 			if (drm_connector_is_cursor_visible(conn)) {
-				ok = ok && set_plane_props(crtc->cursor,
+				ok = ok && set_plane_props(crtc->cursor, crtc->cursor->liftoff_layer,
 					conn->cursor_x, conn->cursor_y, 1);
 			} else {
 				ok = ok && disable_plane(crtc->cursor);
@@ -293,11 +305,6 @@ static bool crtc_commit(struct wlr_drm_connector *conn,
 		goto out;
 	}
 
-	if (liftoff_layer_needs_composition(crtc->primary->liftoff_layer)) {
-		wlr_drm_conn_log(conn, WLR_DEBUG, "Failed to scan-out primary plane");
-		ok = false;
-		goto out;
-	}
 	if (crtc->cursor &&
 			liftoff_layer_needs_composition(crtc->cursor->liftoff_layer)) {
 		wlr_drm_conn_log(conn, WLR_DEBUG, "Failed to scan-out cursor plane");

include/backend/drm/drm.h

@@ -40,6 +40,7 @@ struct wlr_drm_crtc {
 	uint32_t id;
 	struct wlr_drm_lease *lease;
 	struct liftoff_output *liftoff;
+	struct liftoff_layer *liftoff_composition_layer;
 
 	// Atomic modesetting only
 	uint32_t mode_id;