layering: DF MO layering: Fix placement of marked nodes

plugins/org.eclipse.elk.alg.layered/src/org/eclipse/elk/alg/layered/options/LayeringStrategy.java

@@ -73,12 +73,14 @@ public enum LayeringStrategy implements ILayoutPhaseFactory<LayeredPhases, LGrap
      * No node with a higher model order is in a layer before a node with a lower model order.
      * Dummy labels are only placed in layers between real nodes.
      */
+    @ExperimentalPropertyValue
     BF_MODEL_ORDER,
     /**
      * Assumes an intended depth first model order of nodes and creates layers accordingly.
      * Nodes are placed in the next layer until a node does not connect the previous layer.
      * Dummy labels are only placed in layers between real nodes.
      */
+    @ExperimentalPropertyValue
     DF_MODEL_ORDER;
 
     @Override

plugins/org.eclipse.elk.alg.layered/src/org/eclipse/elk/alg/layered/p2layers/DepthFirstModelOrderLayerer.java

@@ -71,6 +71,12 @@ public final class DepthFirstModelOrderLayerer implements ILayoutPhase<LayeredPh
      */
     private List<LNode> nodesToPlace;
 
+    /**
+     * Saves the maximum layer the nodes that still have to be assigned to a layer will be placed in.
+     * This is necessary to determine the actual offset of the nodes to place.
+     */
+    private int maxToPlace = 0;
+
     @Override
     public LayoutProcessorConfiguration<LayeredPhases, LGraph> getLayoutProcessorConfiguration(final LGraph graph) {
         return BASELINE_PROCESSING_CONFIGURATION;
@@ -124,7 +130,7 @@ public void process(final LGraph thelayeredGraph, final IElkProgressMonitor moni
                         if (layerDiff > 0) {
                             // Case some dependency to the existing graph was found add all nodes to their layers.
                             for (LNode toPlace : nodesToPlace) {
-                                toPlace.id += maxLayer;
+                                toPlace.id += maxLayer - maxToPlace;
                             }
                             placeNodesToPlace();
                             // Remove all nodes since they are now placed correctly.
@@ -134,6 +140,7 @@ public void process(final LGraph thelayeredGraph, final IElkProgressMonitor moni
                             // Case nodes cannot be placed without the need to move them later.
                             nodesToPlace.add(node);
                             node.id = desiredLayer;
+                            maxToPlace = Math.max(maxToPlace, desiredLayer);
                             // Add dummy nodes and give them their desired layer id.
                             for (LEdge edge : node.getIncomingEdges()) {
                                 if (edge.getSource().getNode().getLayer() == null
@@ -164,6 +171,7 @@ public void process(final LGraph thelayeredGraph, final IElkProgressMonitor moni
                         // Case no incoming connections, save the node to be placed.
                         nodesToPlace.add(node);
                         node.id = 0; // Save the layer the node will be placed in.
+                        maxToPlace = Math.max(maxToPlace, 0);
                         currentLayer = layeredGraph.getLayers().get(0);
                         currentLayerId = 0;
 
@@ -292,6 +300,7 @@ private int getMaxConnectedLayer(final int layerId, final LNode node) {
      * Places the nodes to place in their desired layer.
      */
     public void placeNodesToPlace() {
+        maxToPlace = 0;
         for (LNode nodeToPlace : nodesToPlace) {
             if (nodeToPlace.id >= layeredGraph.getLayers().size()) {
                 // Add a normal and a dummy layer.