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While most layout options are used to affect how the active layout algorithm computes concrete coordinates for the graph elements, there are some layout options that have a special role in KIML.

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layoutAlgorithm layoutAlgorithm

Layout Algorithm

The option with identifier de.cau.cs.kieler.algorithm specifies which layout algorithm to use for a graph or subgraph. The value can be either the identifier of a layout algorithm or the identifier of a layout type. In the latter case the algorithm with highest priority of that type is applied. It is possible to set different values for this option on subgraphs of a hierarchical graph, where a subgraph is identified by a parent node. A layout algorithm is responsible to process only the direct content of a given parent node. An exception from this rule is made when the Layout Hierarchy option is active.

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• Layered - The layer-based method emphasizes the direction of edges by pointing as many edges as possible into the same direction. The nodes are arranged in layers and then reordered such that the number of edge crossings is minimized. Afterwards, concrete coordinates are computed for the nodes and edge bend points.
• Orthogonal - Orthogonal methods follow the "topology-shape-metrics" approach, which first applies a planarization technique, resulting in a planar representation of the graph, then compute an orthogonal shape, and finally determine concrete coordinates for nodes and edge bend points by applying a compaction method.
• Force - Layout algorithms that follow physical analogies by simulating a system of attractive and repulsive forces.
• Circular - Circular layout algorithms emphasize biconnected components of a graph by arranging them in circles. This is useful if a drawing is desired where such components are clearly grouped, or where cycles are shown as prominent properties of the graph.
• Tree - Specialized layout methods for trees, i.e. acyclic graphs. The regular structure of graphs that have no undirected cycles can be emphasized using an algorithm of this type.

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diagramType diagramType

Diagram Type

Diagram types are used to classify graphical diagrams for setting default layout option values for a set of similar diagrams. The diagram type of an element is specified with the layout option de.cau.cs.kieler.diagramType. Layout algorithms can declare which diagram types they support well, and give a priority value for each supported type. KIML decides at runtime which layout algorithm has the highest priority for a given diagram, so that the most suitable algorithm is always used. Usual values for such priorities are between 1 and 10, where the highest value should only be assigned if the algorithm is especially designed for diagrams of the respective type, or if it has proven to be very adequate for them. Lower values should be given if the algorithm is able to draw the diagrams correctly, but with lower quality of the resulting layout.

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• General - This type is automatically assigned to all diagrams for which no specific type is declared. A layout algorithm that has the highest priority on the General diagram type is taken as the default algorithm when no further information on a diagram is available to KIML.
• State Machine - All kinds of state machines, automata, and activity diagrams. Examples: SCCharts / SyncCharts, UML Activity diagrams.
• Data Flow Diagram - Actor-oriented diagrams, where connections are mostly done between ports of nodes. These diagrams can only be handled properly by very special layout algorithms, such as those developed in the KLay project.
• Class Diagram - Class diagrams such as Ecore diagrams for the EMF or UML Class diagrams.
• Use Case Diagram - Use case diagrams as defined by the UML.
• Unconnected Boxes - Sets of nodes that have no connections and are treated as resizable boxes. This is related to mathematical packing problems. Example: Regions in SCCharts / SyncCharts.

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edgeRouting edgeRouting

Edge Routing

This option influences the way in which edges are routed between the nodes they connect. The following settings are available:

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1. Start at the source point of the edge.
2. As long as there are at least three bend points left:
   1. Draw a cubic spline segment to the third bend point with the other two bend points as control points.
   2. Use the third bend point as start point for the next segment.
   3. Consume the three bend points and proceed to the next segment.
3. Check the number of remaining bend points:
   1. Two bend points – draw a cubic spline segment to the target point of the edge.
   2. One bend point – draw a quadratic spline segment to the target point of the edge.
   3. No bend point – draw a straight line to the target point of the edge.

Other Options

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addPortSpace addPortSpace

Additional Port Space

This option controls additional port space left around the set of ports on each side:

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This option is only relevant if port constraints are FREE, FIXED_SIDE, or FIXED_ORDER. If size constraints include PORTS, the additional port space, together with the port spacing and the size of ports, determines a lower bound on the node size.

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alignment alignment

Alignment

Determines the alignment of a node in relation to other nodes of the same row or column. For layer-based algorithms, for instance, this option controls how a node is positioned inside its assigned layer.

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aspectRatio aspectRatio

Aspect Ratio

The aspect ratio of a drawing is the ratio of its total width to its total height. This option gives some control over that ratio, although in most cases it is only interpreted as a hint on how to arrange multiple connected components, hence the actual aspect ratio will probably be different from what has been specified with the option.

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commentBox commentBox

Comment Box

A node that is marked as comment box is treated as a label that needs to be placed somewhere. In contrast to normal node labels (modeled with a KLabel instance), comment boxes may have connections to other nodes, as in the following example.

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hypernode hypernode

Hypernode

A node that is marked as hypernode has a special role in the graph structure, since all its incident edges are treated as parts of the same hyperedge. Example: relation vertices in Ptolemy models.

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layoutHierarchy layoutHierarchy

Layout Hierarchy

If this option is supported and active, the layout algorithm is requested to process the full hierarchy contained in the input node. This means that instead of executing another algorithm on each hierarchy level, all levels are arranged in a single algorithm execution.

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noLayout noLayout

No Layout

Elements that are marked with this option are excluded from layout. This is used to identify diagram objects that should not be regarded as graph elements.

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portAnchor portAnchor

Port Anchor Offset

Since ports have a size, we need a concrete point inside the port that edges should start or end in. In KLay Layered, this is referred to as the port anchor. By default, the center of each port is used as its port anchor, but this behavior can be overridden by setting an explicit port anchor.

In the following example, the port anchor of the left port was moved upwards, while the port anchor of the second port was moved downwards:

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portOffset portOffset

Port Offset

The port offset is used to specify how much space a layout algorithm should leave between a port and the border of its node. This is usually zero, but doesn't have to be. If the offset is not defined for a given port, a layout algorithm can try to infer the offset from the port's coordinates and its node's size in the input graph. This of course requires both properties to be set to sensible values.

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• The port constraints on a node are set to FREE, FIXED_SIDES or FIXED_ORDER.
• The port constraints on a node are set to FIXED_RATIO or FIXED_POS, and the size of the node is not fixed. (Note that this is especially true for ports of compound nodes.)

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portSpacing portSpacing

Port Spacing

The port spacing determines how much space KLay Layered should leave between the ports of each side. This option is only relevant if the node size depends on the ports, that is, if the size constraints include SizeConstraint.PORTS.