Rendering

build.gradle.kts

@@ -2,7 +2,7 @@ plugins {
     kotlin("jvm") version "2.2.0"
 }
 
-group = "be.topl.phoenix-intellij"
+group = "com.jaytux.altgraph"
 version = "1.0-SNAPSHOT"
 
 repositories {

src/main/kotlin/com/jaytux/altgraph/core/BaseGraph.kt

@@ -1,5 +1,19 @@
 package com.jaytux.altgraph.core
 
+/**
+ * A mutable directed graph implementation, with arbitrary vertex and edge types. Supports marking vertices as "roots"
+ * during addition.
+ *
+ * Vertices and edges must be unique (no duplicates allowed). Edges are directed, and there can be at most one edge
+ * from a given vertex `A` to another vertex `B`.
+ *
+ * All operations that attempt to violate these constraints will throw a [GraphException].
+ *
+ * @param V The vertex type.
+ * @param E The edge type.
+ * @see [IMutableGraph]
+ * @see [IGraph]
+ */
 open class BaseGraph<V, E> : IMutableGraph<V, E> {
     private val _vertices = mutableMapOf<V, Boolean>()
     // [from] -> {e: exists v s.t. e = (from, v)}
@@ -70,6 +84,15 @@ open class BaseGraph<V, E> : IMutableGraph<V, E> {
         if (_existing[from]?.isEmpty() == true) { _existing.remove(from) }
     }
 
+    /**
+     * Returns an immutable view of this graph.
+     *
+     * Further modifications to the original graph will be reflected in the immutable view.
+     *
+     * This operations is very cheap, as it does not involve any copying of data.
+     *
+     * @return An immutable view of this graph
+     */
     fun immutable(): IGraph<V, E> = BaseGraphImmutable()
 
     override fun successors(vertex: V): Map<V, E> =

src/main/kotlin/com/jaytux/altgraph/core/IGraph.kt

@@ -1,42 +1,221 @@
 package com.jaytux.altgraph.core
 
+/**
+ * A simple, immutable graph interface.
+ *
+ * The graph is directed, and may contain cycles (including self-loops). However, it may not contain parallel edges.
+ *
+ * The supported operations are:
+ * - Querying for vertices and edges;
+ * - Querying for graph roots (these do not have to be roots in the traditional sense, but can be any vertex that
+ * should be treated as a root for layout purposes);
+ * - Querying for successors and predecessors of a vertex;
+ * - Querying for the edge between two vertices, if it exists.
+ *
+ * Importantly, each vertex (`V`) and edge (`E`) should be unique in the graph. Edges should not encode any incidence
+ * information (i.e. their endpoints), but should be distinct objects.
+ *
+ * Mutable graphs should implement [IMutableGraph], which extends this interface with mutation operations.
+ *
+ * @param V the type of vertices in the graph
+ * @param E the type of edges in the graph
+ * @see IMutableGraph
+ * @see BaseGraph
+ */
 interface IGraph<V, E> {
+    /**
+     * Gets all the vertices in the graph.
+     *
+     * @return a set of all vertices in the graph
+     */
     fun vertices(): Set<V>
+
+    /**
+     * Gets all the edges in the graph, along with their endpoints.
+     *
+     * @return a map from edges to their endpoints (as pairs (from, to))
+     */
     fun edges(): Map<E, Pair<V, V>>
+
+    /**
+     * Gets all the root vertices in the graph.
+     *
+     * @return a set of all root vertices in the graph
+     */
     fun roots(): Set<V>
 
+    /**
+     * Gets the successors of a given vertex, along with the connecting edges.
+     *
+     * A default implementation is provided in the [IGraph] interface, but may be overridden for efficiency.
+     *
+     * @param vertex the vertex whose successors are to be found
+     * @return a map from successor vertices to their outgoing edges
+     * @see predecessors
+     */
     fun successors(vertex: V): Map<V, E> =
         edges().filter { it.value.first == vertex }
             .map { (edge, pair) -> pair.second to edge }.toMap()
 
+    /**
+     * Gets the predecessors of a given vertex, along with the connecting edges.
+     *
+     * A default implementation is provided in the [IGraph] interface, but may be overridden for efficiency.
+     *
+     * @param vertex the vertex whose predecessors are to be found
+     * @return a map from predecessor vertices to their incoming edges
+     * @see successors
+     */
     fun predecessors(vertex: V): Map<V, E> =
         edges().filter { it.value.second == vertex }
             .map { (edge, pair) -> pair.first to edge }.toMap()
 
+    /**
+     * Checks whether an edge exists between two vertices, and returns it if so.
+     *
+     * A default implementation is provided in the [IGraph] interface, but may be overridden for efficiency.
+     *
+     * @param x the starting vertex
+     * @param y the ending vertex
+     * @return the edge from `x` to `y`, or `null` if no such edge exists
+     */
     fun xToY(x: V, y: V): E? = edges().entries.firstOrNull { it.value == x to y }?.key
 }
 
+/**
+ * A simple, mutable graph interface, extending [IGraph].
+ *
+ * In addition to the operations provided by [IGraph], mutable graphs support:
+ * - Adding and removing vertices;
+ * - Connecting and disconnecting vertices with edges.
+ *
+ * The same restrictions apply as for [IGraph]: the graph is directed, can contain cycles (including self-loops), can't
+ * contain parallel edges, and vertex (`V`) and edge (`E`) objects should be unique in the graph.
+ *
+ * Immutable graphs should implement [IGraph].
+ *
+ * @param V the type of vertices in the graph
+ * @param E the type of edges in the graph
+ * @see IGraph
+ * @see BaseGraph
+ */
 interface IMutableGraph<V, E> : IGraph<V, E> {
+    /**
+     * Adds a vertex to the graph.
+     *
+     * @param vertex the vertex to add
+     * @param isRoot whether the vertex should be considered a root (by default, `false`)
+     * @return the added vertex
+     * @throws GraphException if the vertex already exists in the graph
+     */
     fun addVertex(vertex: V, isRoot: Boolean = false): V
+
+    /**
+     * Removes a vertex from the graph.
+     *
+     * If the vertex has any incident edges (i.e. incoming or outgoing edges), they are also removed.
+     *
+     * @param vertex the vertex to remove
+     * @throws GraphException if the vertex does not exist in the graph
+     */
     fun removeVertex(vertex: V)
+
+    /**
+     * Connects two vertices with an edge.
+     *
+     * @param from the starting vertex
+     * @param to the ending vertex
+     * @param edge the edge to add between `from` and `to`
+     * @return the added edge
+     * @throws GraphException if either vertex does not exist in the graph, if the edge already exists in the graph,
+     * or if there is already an edge between `from` and `to`.
+     */
     fun connect(from: V, to: V, edge: E): E
+
+    /**
+     * Disconnects two vertices by removing the edge between them.
+     *
+     * @param from the starting vertex
+     * @param to the ending vertex
+     * @throws GraphException if there is no edge between `from` and `to`
+     */
     fun disconnect(from: V, to: V)
+
+    /**
+     * Removes an edge from the graph.
+     *
+     * @param edge the edge to remove
+     * @throws GraphException if the edge does not exist in the graph
+     */
     fun removeEdge(edge: E)
 }
 
+/**
+ * Exception thrown when a graph operation fails.
+ *
+ * @param message the exception message
+ */
 class GraphException(message: String) : RuntimeException(message) {
     companion object {
+        /**
+         * Constructs a [GraphException] indicating that a vertex already exists in the graph.
+         *
+         * @param V the type of vertices in the graph
+         * @param vertex the vertex that already exists
+         * @return a [GraphException] with an appropriate message
+         */
         fun <V> vertexAlreadyExists(vertex: V) =
             GraphException("Vertex '$vertex' already exists in this graph.")
+
+        /**
+         * Constructs a [GraphException] indicating that an edge already exists in the graph.
+         *
+         * @param E the type of edges in the graph
+         * @param edge the edge that already exists
+         * @return a [GraphException] with an appropriate message
+         */
         fun <E> edgeAlreadyExists(edge: E) =
             GraphException("Edge '$edge' already exists in this graph.")
+
+        /**
+         * Constructs a [GraphException] indicating that an edge already exists between two vertices in the graph.
+         *
+         * @param V the type of vertices in the graph
+         * @param from the starting vertex
+         * @param to the ending vertex
+         * @return a [GraphException] with an appropriate message
+         */
         fun <V> edgeBetweenAlreadyExists(from: V, to: V) =
             GraphException("Edge from '$from' to '$to' already exists in this graph.")
 
+        /**
+         * Constructs a [GraphException] indicating that a vertex was not found in the graph.
+         *
+         * @param V the type of vertices in the graph
+         * @param vertex the vertex that was not found
+         * @return a [GraphException] with an appropriate message
+         */
         fun <V> vertexNotFound(vertex: V) =
             GraphException("Vertex '$vertex' not found in this graph.")
+
+        /**
+         * Constructs a [GraphException] indicating that no edge was found between two vertices in the graph.
+         *
+         * @param V the type of vertices in the graph
+         * @param from the starting vertex
+         * @param to the ending vertex
+         * @return a [GraphException] with an appropriate message
+         */
         fun <V> noEdgeFound(from: V, to: V) =
             GraphException("No edge found from '$from' to '$to' in this graph.")
+
+        /**
+         * Constructs a [GraphException] indicating that an edge was not found in the graph.
+         *
+         * @param E the type of edges in the graph
+         * @param edge the edge that was not found
+         * @return a [GraphException] with an appropriate message
+         */
         fun <E> edgeNotFound(edge: E) =
             GraphException("Edge '$edge' not found in this graph.")
     }

src/main/kotlin/com/jaytux/altgraph/examples/SimpleCFG.kt

@@ -0,0 +1,51 @@
+package com.jaytux.altgraph.examples
+
+import com.jaytux.altgraph.core.BaseGraph
+import com.jaytux.altgraph.core.IGraph
+import com.jaytux.altgraph.layout.PseudoForestLayout
+import com.jaytux.altgraph.swing.DefaultVertexComponent
+import com.jaytux.altgraph.swing.GraphPane
+import javax.swing.JFrame
+import javax.swing.SwingUtilities
+
+fun getGraph(): IGraph<String, Int> {
+    val graph = BaseGraph<String, Int>()
+    // vertices
+    val entry = graph.addVertex("[ENTRY]", true)
+    val exit = graph.addVertex("[EXIT]")
+    val labels = intArrayOf(198, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210).associateWith { graph.addVertex(".label_$it") }
+
+    var count = 0
+    graph.connect(entry, labels[198]!!, count++)
+    arrayOf(
+        198 to 200, 200 to 201, 200 to 202, 201 to 203, 201 to 204, 203 to 200, 204 to 205, 205 to 208, 208 to 209,
+        209 to 200, 209 to 210, 210 to 208, 204 to 206, 206 to 207, 207 to 208
+    ).forEach { (from, to) -> graph.connect(labels[from]!!, labels[to]!!, count++) }
+    graph.connect(labels[202]!!, exit, count++)
+    return graph
+}
+
+fun getPane(graph: IGraph<String, Int>): GraphPane<String, Int> {
+    val pane = GraphPane(graph) { pane, graph ->
+        PseudoForestLayout(graph, 10.0f, 20.0f, 10.0f) { v ->
+            (pane.getComponentFor(v) as DefaultVertexComponent).vertexSize()
+        }
+    }
+    return pane
+}
+
+fun main() {
+    val graph = getGraph()
+    val pane = getPane(graph)
+
+    // show pane in window
+    SwingUtilities.invokeLater {
+        val frame = JFrame("Simple Control Flow Graph")
+        frame.defaultCloseOperation = JFrame.EXIT_ON_CLOSE
+        frame.setSize(800, 600)
+        frame.add(pane)
+        frame.pack()
+        frame.setLocationRelativeTo(null)
+        frame.isVisible = true
+    }
+}

src/main/kotlin/com/jaytux/altgraph/layout/Geometry.kt

@@ -1,13 +1,29 @@
 package com.jaytux.altgraph.layout
 
-interface ISize<S : ISize<S>> {
-    fun width(): Float
-    fun height(): Float
-    fun copy(width: Float, height: Float): S
-}
+/**
+ * A simple 2D size.
+ *
+ * This class is intentionally kept simple to easily allow wrapping library-specific size classes.
+ *
+ * @property width the width
+ * @property height the height
+ */
+data class GSize(var width: Float, var height: Float)
 
-interface IPoint<P : IPoint<P>> {
-    fun x(): Float
-    fun y(): Float
-    fun copy(x: Float, y: Float): P
+/**
+ * A simple 2D point.
+ *
+ * This class is intentionally kept simple to easily allow wrapping library-specific point classes.
+ *
+ * @property x the x coordinate
+ * @property y the y coordinate
+ */
+data class GPoint(var x: Float, var y: Float) {
+    /**
+     * Adds two points component-wise.
+     *
+     * @param other the other point to add
+     * @return a new point representing the sum of this point and [other]
+     */
+    operator fun plus(other: GPoint): GPoint = GPoint(x + other.x, y + other.y)
 }

src/main/kotlin/com/jaytux/altgraph/layout/ILayout.kt

@@ -2,12 +2,76 @@ package com.jaytux.altgraph.layout
 
 import com.jaytux.altgraph.core.IGraph
 
-interface ILayout<V, E, P : IPoint<P>, S : ISize<S>> {
+/**
+ * A layout algorithm for graphs.
+ *
+ * The layout algorithm is responsible for positioning vertices in 2D space.
+ *
+ * The layout algorithm should cache the results of the (expensive) [compute] operation, such that the [location] and
+ * [boundingBox] operation can be performed efficiently.
+ * However, it is not required to invalidate the cache when [setGraph] or other mutating operations are called.
+ *
+ * @param V the vertex type
+ * @param E the edge type
+ */
+interface ILayout<V, E> {
+    /**
+     * Gets the graph to layout.
+     *
+     * @return the graph
+     */
     fun graph(): IGraph<V, E>
+
+    /**
+     * Sets the graph to layout.
+     *
+     * @param graph the graph
+     */
     fun setGraph(graph: IGraph<V, E>)
+
+    /**
+     * Computes the layout.
+     *
+     * The computation results should be cached for future calls to [location] and [boundingBox].
+     */
     fun compute()
-    fun location(vertex: V): P
-    fun freezeAt(vertex: V, point: P)
+
+    /**
+     * Gets the location of a vertex.
+     *
+     * If the layout has not been computed yet, this should invoke [compute].
+     * However, if the layout has been computed, this should return the cached location.
+     */
+    fun location(vertex: V): GPoint
+
+    /**
+     * Freezes a vertex at a specific point.
+     *
+     * Not all layout algorithms support freezing vertices; check the documentation of the specific implementation.
+     * Additionally, the algorithms that support freezing may restrict which vertices can be frozen, or put restrictions
+     * on the position of frozen vertices.
+     *
+     * A frozen vertex will not be moved by subsequent calls to [compute] until it is unfrozen.
+     *
+     * @param vertex the vertex to freeze
+     * @param point the point to freeze the vertex at
+     */
+    fun freezeAt(vertex: V, point: GPoint)
+
+    /**
+     * Unfreezes a vertex, allowing it to be moved by subsequent calls to [compute].
+     *
+     * If an implementation does not support freezing vertices, this method should do nothing.
+     *
+     * @param vertex the vertex to unfreeze
+     */
     fun unfreeze(vertex: V)
-    fun boundingBox(): S
+
+    /**
+     * Gets the bounding box of the layout.
+     *
+     * If the layout has not been computed yet, this should invoke [compute].
+     * However, if the layout has been computed, this should return the cached bounding box.
+     */
+    fun boundingBox(): GSize
 }

src/main/kotlin/com/jaytux/altgraph/layout/MutablePair.kt

@@ -1,3 +0,0 @@
-package com.jaytux.altgraph.layout
-
-data class MutablePair<T1, T2>(var x: T1, var y: T2)

src/main/kotlin/com/jaytux/altgraph/layout/PseudoForestLayout.kt

@@ -8,37 +8,83 @@ import kotlin.concurrent.atomics.AtomicBoolean
 import kotlin.concurrent.atomics.ExperimentalAtomicApi
 import kotlin.math.max
 
-class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
+/**
+ * A Sugiyama-style layout algorithm for "pseudo-forests" (such as control-flow graphs).
+ *
+ * This algorithm arranges the graph in layers, attempting to minimize edge crossings and distribute nodes evenly.
+ * It treats the graph as a collection of disjoint acyclic graphs, disregarding back-edges during layout.
+ *
+ * This layout algorithm does not support freezing vertices; calling [freezeAt] will throw
+ * [UnsupportedOperationException], and [unfreeze] is a no-op.
+ * Additionally, [setGraph] and [setVertexSize] do not invalidate the cache.
+ *
+ * All mutation operations are synchronized, and thread-safe. However, the layout is not incremental, and doesn't track
+ * graph changes. Any change to the graph or vertex sizes requires a full recomputation of the layout. The synchronized
+ * operations are:
+ * - Changing the graph ([setGraph]), measuring ([setVertexSize]),
+ * - Querying layout-dependent values ([location], [boundingBox]),
+ * - Computing the layout ([compute]).
+ *
+ * Locking is done via a simple spin-lock.
+ *
+ * @param V the vertex type
+ * @param E the edge type
+ * @param graph the graph to layout
+ * @property horizontalMargin the horizontal margin between vertices in the same layer
+ * @property disjoinXMargin the horizontal margin between disjoint subgraphs
+ * @property interLayer the vertical margin between layers
+ * @property vertexSize a function that returns the size of a vertex, including its label offset
+ *
+ * @see ILayout
+ */
+class PseudoForestLayout<V, E>(
     graph: IGraph<V, E>,
     var horizontalMargin: Float,
     var disjoinXMargin: Float,
     var interLayer: Float,
-    val pointZero: P, val sizeZero: S,
-    vertexSize: (V) -> VertexSize<P, S>
-) : ILayout<V, E, P, S> {
-    data class VertexSize<P : IPoint<P>, S : ISize<S>>(val vertex: S, val labelOffset: P, val labelSize: S) {
-        fun fullSize(): S { // TODO: check the math here
-            val minX = 0 + labelOffset.x()
-            val minY = 0 + labelOffset.y()
-            val maxX = vertex.width() + labelOffset.x() + labelSize.width()
-            val maxY = vertex.height() + labelOffset.y() + labelSize.height()
-            return vertex.copy(
+    vertexSize: (V) -> VertexSize
+) : ILayout<V, E>
+{
+    /**
+     * A class representing data on the size of a vertex, including its label offset and size.
+     *
+     * @property vertex the size of the vertex itself
+     * @property labelOffset the offset of the label relative to the vertex's center
+     * @property labelSize the size of the label
+     */
+    data class VertexSize(val vertex: GSize, val labelOffset: GPoint, val labelSize: GSize) {
+        /**
+         * Calculates the full size of the vertex including its label and offset.
+         *
+         * @return the full size of the vertex
+         */
+        fun fullSize(): GSize { // TODO: check the math here
+            val minX = 0 + labelOffset.x
+            val minY = 0 + labelOffset.y
+            val maxX = vertex.width + labelOffset.x + labelSize.width
+            val maxY = vertex.height + labelOffset.y + labelSize.height
+            return GSize(
                 width = maxX - minX,
                 height = maxY - minY
             )
         }
 
-        fun vCenterInBox(): P { // TODO: check the math here
-            return labelOffset.copy(
-                x = labelOffset.x() + vertex.width() / 2,
-                y = labelOffset.y() + vertex.height() / 2
+        /**
+         * Calculates the center point of the vertex within its bounding box.
+         *
+         * @return the center point of the vertex
+         */
+        fun vCenterInBox(): GPoint { // TODO: check the math here
+            return GPoint(
+                x = labelOffset.x + vertex.width / 2,
+                y = labelOffset.y + vertex.height / 2
             )
         }
     }
     private var _graph: IGraph<V, E> = graph
-    private val _positions = mutableMapOf<V, P>()
-    private var _vertexSize: (V) -> VertexSize<P, S> = vertexSize
-    private var _boundingBox: S? = null
+    private val _positions = mutableMapOf<V, GPoint>()
+    private var _vertexSize: (V) -> VertexSize = vertexSize
+    private var _boundingBox: GSize? = null
 
     @OptIn(ExperimentalAtomicApi::class)
     private var _lock: AtomicBoolean = AtomicBoolean(false)
@@ -50,18 +96,26 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
         }
 
         try {
+            println("Took lock in ${Exception().stackTrace.first()}")
             val x = block()
             _lock.store(false) // unlock after operation
             return x
         }
         finally {
+            println("Releasing lock in ${Exception().stackTrace.first()}")
             _lock.store(false) // we can safely unlock
         }
     }
 
     override fun graph(): IGraph<V, E> = _graph
     override fun setGraph(graph: IGraph<V, E>) { locked { _graph = graph } }
-    fun setVertexSize(vertexSize: (V) -> VertexSize<P, S>) { locked { _vertexSize = vertexSize } }
+
+    /**
+     * Sets the vertex measuring function.
+     *
+     * @param vertexSize a function that returns the size of a vertex, including its label offset
+     */
+    fun setVertexSize(vertexSize: (V) -> VertexSize) { locked { _vertexSize = vertexSize } }
 
     // Either a vertex, or a dummy node to break up multi-layer-spanning edges
     private data class Connector<V>(
@@ -114,29 +168,36 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
     }
 
     override fun compute() {
+        println("Acquiring lock")
         locked {
+            print("Starting layouting")
             _positions.clear()
 
             // Assign a layer to each vertex by traversing depth-first and ignoring back-edges.
             val roots = _graph.roots()
             if (roots.isEmpty()) { // Only reachable nodes matter.
-                _boundingBox = sizeZero
+                _boundingBox = GSize(0.0f, 0.0f)
                 return
             }
             val layers = mutableMapOf<V, Pair<Int, MutableSet<V>>>()
             val queue = ArrayDeque<Pair<V, Set<V>>>(roots.size * 2)
             queue.addAll(roots.map { it to emptySet() })
+            println(" - Computing layers from roots: $roots")
 
             while (!queue.isEmpty()) {
                 val (vertex, onPath) = queue.removeFirst()
                 val (layer, dep) = layers.getOrPut(vertex) { 0 to mutableSetOf() }
+                println("   - Visiting $vertex (layer $layer), path=$onPath, deps=$dep")
 
                 val succLayer = layer + 1
                 _graph.successors(vertex).forEach { (succ, _) ->
+                    if (succ in onPath) return@forEach
                     dep += succ
 
-                    if (succ in onPath) return@forEach
                     layers[succ]?.let { (l, sDep) ->
+                        println("     - Successor $succ already had layer $l (might be increased, along with its dependents)")
+                        dep += sDep
+
                         val delta = succLayer - l
                         if (delta > 0) {
                             layers[succ] = succLayer to (sDep)
@@ -145,27 +206,36 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
                                     ?: (succLayer to mutableSetOf())
                             }
                         }
+                    } ?: run {
+                        layers[succ] = succLayer to mutableSetOf()
                     }
+                    println("     - Adding successor to queue: $succ (layer: ${layers[succ]?.first})")
                     queue.addLast(succ to onPath + vertex)
                 }
+
+                // ensure dependents are always up to date
+                layers.values.filter { it.second.contains(vertex) }.forEach { (_, d) -> d.addAll(dep) }
             }
+            println(" - Assigned layers:")
+            layers.forEach { (v, p) -> println("   - Vertex $v: layer ${p.first}, dependents: ${p.second}") }
 
             // Cache node sizes
             val vertexSizes = layers.mapValues { (v, _) -> _vertexSize(v).let { it.fullSize() to it.vCenterInBox() } }
 
             // Compute layer y positions (and thus the bounding box height).
-            val layerCount = layers.maxOf { it.value.first }
+            val layerCount = layers.maxOf { it.value.first } + 1
             val layerHeights = MutableList(layerCount) { 0.0f }
+            println(" - Have $layerCount layers")
 
             var minOffset = Float.POSITIVE_INFINITY
             var maxOffset = Float.NEGATIVE_INFINITY
             layers.forEach { (vertex, pair) ->
                 val (layer, _) = pair
                 val size = vertexSizes[vertex]!!
-                layerHeights[layer] = max(layerHeights[layer], size.first.height())
+                layerHeights[layer] = max(layerHeights[layer], size.first.height)
                 if(layer == 0) {
                     // Take into account vertex bounding box offset
-                    val delta = size.second.y()
+                    val delta = size.second.y
                     if(delta < minOffset) minOffset = delta
                     if(delta > maxOffset) maxOffset = delta
                 }
@@ -178,9 +248,17 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
                 y
             }
 
+            println(" - Layer measurements: (height, y) = ${(layerHeights zip layerY)}")
+            println(" - Layers with nodes:")
+            for(i in 0 until layerCount) {
+                val verts = layers.filter { it.value.first == i }.keys
+                println("   - Layer $i: $verts")
+            }
+
             // Compute disjoint graphs
             val disjoint = roots.fold(listOf<Set<V>>()) { acc, root ->
                 val reachable = layers[root]?.second?.toMutableSet() ?: return@fold acc
+                reachable += root
 
                 val dedup = acc.mapNotNull { other ->
                     val inter = reachable intersect other
@@ -196,6 +274,7 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
             }
             var currentXZero = 0.0f
             disjoint.forEach { sub ->
+                println(" - Layouting disjoint subgraph: $sub")
                 // Put each vertex in a list by layer
                 val layered = List(layerCount) { layer ->
                     sub.mapNotNull {
@@ -204,6 +283,9 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
                     }.toMutableList()
                 }
 
+                println("   - Initial layered vertices:")
+                layered.forEachIndexed { idx, list -> println("     - Layer $idx: $list") }
+
                 // Break up multi-layer edges with dummy nodes
                 layered.forEachIndexed { idx, list ->
                     list.forEach { v ->
@@ -223,6 +305,15 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
                 }
 
                 val layerWidths = MutableList(layerCount) { -horizontalMargin } // avoid double adding margin on 1st node
+
+                // Layout roots
+                layered[0].forEach { root ->
+                    root.x.fold({ node ->
+                        val w = vertexSizes[node]!!.first.width
+                        layerWidths[0] += w + horizontalMargin
+                    }) {}
+                }
+
                 // Layer-by-layer, assign x slots (not yet positions)
                 for(i in 1 until layered.size) {
                     // Barycenter heuristic: average of parents' slots
@@ -234,7 +325,7 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
 
                     layered[i].forEach { v ->
                         v.x.fold({ node ->
-                            val w = vertexSizes[node]!!.first.width()
+                            val w = vertexSizes[node]!!.first.width
                             layerWidths[i] += w + horizontalMargin
                         }) { /* do nothing */ }
                     }
@@ -247,12 +338,14 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
 
                 // Assign x positions
                 layered.forEachIndexed { idx, layer ->
+                    println("   - Positioning layer $idx")
                     var currentX = currentXZero + (maxWidth - layerWidths[idx]) / 2
                     layer.forEach { v ->
                         v.x.fold({ node ->
                             val offset = vertexSizes[node]!!.second
-                            _positions[node] = pointZero.copy(x = currentX + offset.x(), y = layerY[idx] + offset.y())
-                            currentX += vertexSizes[node]!!.first.width() + horizontalMargin
+                            _positions[node] = GPoint(x = currentX + offset.x, y = layerY[idx] + offset.y)
+                            println("     - Put vertex $node at ${_positions[node]}")
+                            currentX += vertexSizes[node]!!.first.width + horizontalMargin
                         }) { /* do nothing */ }
                     }
                 }
@@ -263,20 +356,22 @@ class PseudoForestLayout<V, E, P : IPoint<P>, S : ISize<S>>(
 
             // Compute the bounding box
             // min x and y are 0
-            _boundingBox = sizeZero.copy(currentXZero - disjoinXMargin, layerY.last() + layerHeights.last() / 2 + offset)
+            _boundingBox = GSize(currentXZero - disjoinXMargin, layerY.last() + layerHeights.last() / 2 + offset)
+            println("Done layouting")
         }
+        println("Released lock")
     }
 
-    override fun location(vertex: V): P {
-        if(vertex !in _graph.vertices()) throw GraphException.vertexNotFound(vertex)
+    override fun location(vertex: V): GPoint {
+        if (vertex !in _graph.vertices()) throw GraphException.vertexNotFound(vertex)
         return _positions[vertex] ?: run {
             compute()
-            _positions[vertex]!!
+            _positions[vertex] ?: throw IllegalArgumentException("Vertex $vertex was not layout-ed: $_positions")
         }
     }
 
-    override fun freezeAt(vertex: V, point: P) = throw UnsupportedOperationException("PseudoForestLayout does not allow freezing vertices.")
+    override fun freezeAt(vertex: V, point: GPoint) = throw UnsupportedOperationException("PseudoForestLayout does not allow freezing vertices.")
     override fun unfreeze(vertex: V) { /* no-op: cannot freeze vertices */ }
 
-    override fun boundingBox(): S = _boundingBox ?: run { compute(); _boundingBox!! }
+    override fun boundingBox(): GSize = locked { _boundingBox ?: run { compute(); _boundingBox!! } }
 }

src/main/kotlin/com/jaytux/altgraph/layout/SumType.kt

@@ -1,25 +1,80 @@
 package com.jaytux.altgraph.layout
 
+/**
+ * A sum type (aka tagged union, variant, discriminated union) of two types.
+ *
+ * At any time, a SumType holds either a `T1` or a `T2` value.
+ *
+ * @param T1 the first type
+ * @param T2 the second type
+ */
 sealed class SumType<out T1, out T2> {
+    /**
+     * The first alternative of the sum type.
+     *
+     * This class overrides both [equals] and [hashCode] to refer through to the contained value.
+     * Specifically, equality is defined such that only the following hold:
+     * - `SumT1(x) == SumT1(y)` if and only if `x == y`; or
+     * - `SumT1(x) == y` if and only if `x == y`.
+     *
+     * @param T1 the type of the value
+     * @property value the value
+     */
     class SumT1<out T1>(val value: T1) : SumType<T1, Nothing>() {
         override fun equals(other: Any?): Boolean =
-            other is SumT1<*> && value == other.value
+            (other is SumT1<*> && value == other.value) || value == other
         override fun hashCode(): Int = value.hashCode()
     }
 
+    /**
+     * The second alternative of the sum type.
+     *
+     * This class overrides both [equals] and [hashCode] to refer through to the contained value.
+     * Specifically, equality is defined such that only the following hold:
+     * - `SumT2(x) == SumT2(y)` if and only if `x == y`; or
+     * - `SumT2(x) == y` if and only if `x == y`.
+     *
+     * @param T2 the type of the value
+     * @property value the value
+     */
     class SumT2<out T2>(val value: T2) : SumType<Nothing, T2>() {
         override fun equals(other: Any?): Boolean =
-            other is SumT2<*> && value == other.value
+            (other is SumT2<*> && value == other.value) || value == other
         override fun hashCode(): Int = value.hashCode()
     }
 
+    /**
+     * Pattern matches on the sum type.
+     *
+     * If the sum type holds a `T1`, invokes [onT1] with the contained value and returns its result.
+     * Otherwise, invokes [onT2] with the contained value and returns its result.
+     *
+     * @param R the return type of the pattern match
+     * @param onT1 the function to invoke if the sum type holds a `T1`
+     * @param onT2 the function to invoke if the sum type holds a `T2`
+     * @return the result of invoking either [onT1] or [onT2]
+     */
     fun <R> fold(onT1: (T1) -> R, onT2: (T2) -> R): R = when(this) {
         is SumT1 -> onT1(value)
         is SumT2 -> onT2(value)
     }
 
+    override fun toString(): String = fold({ it.toString() }) { it.toString() }
+
     companion object {
+        /**
+         * Constructs a [SumType] holding a `T1`.
+         *
+         * @receiver the value to hold
+         * @return a [SumType] holding the receiver as a `T1`
+         */
         fun <T> T.sum1(): SumType<T, Nothing> = SumT1(this)
+        /**
+         * Constructs a [SumType] holding a `T2`.
+         *
+         * @receiver the value to hold
+         * @return a [SumType] holding the receiver as a `T2`
+         */
         fun <T> T.sum2(): SumType<Nothing, T> = SumT2(this)
     }
 }

src/main/kotlin/com/jaytux/altgraph/swing/DefaultEdge.kt

@@ -0,0 +1,66 @@
+package com.jaytux.altgraph.swing
+
+import java.awt.Color
+import java.awt.Graphics2D
+import java.awt.Point
+import java.awt.Polygon
+import java.awt.geom.QuadCurve2D
+import kotlin.math.atan2
+import kotlin.math.cos
+import kotlin.math.sin
+import kotlin.math.sqrt
+
+class QuadraticEdge<E>(
+    var delta: Float = 0.2f,
+    var arrowLen: Int = 10,
+    var color: Color = Color.BLACK,
+    var arrowAngle: Double = Math.PI / 6.0
+) : IEdgeRenderer<E> {
+    override fun drawEdge(g: Graphics2D, from: Point, to: Point, meta: E, offsetFrom: Float, offsetTo: Float) {
+        val g2 = g.create() as Graphics2D
+        g2.color = color
+
+        val len = from.distance(to).toFloat()
+        val xLen = delta * len
+
+        val fx = from.x.toFloat(); val fy = from.y.toFloat()
+        val tx = to.x.toFloat(); val ty = to.y.toFloat()
+
+        val midX = (fx + tx) / 2
+        val midY = (fy + ty) / 2
+
+
+        val x1 = tx - midX; val y1 = ty - midY
+        val fac = xLen / sqrt(x1 * x1 + y1 * y1)
+
+        val cx = (midX + y1 * fac)
+        val cy = (midY - x1 * fac)
+
+        val dx1 = cx - fx; val dy1 = cy - fy; val d1fac = offsetFrom / sqrt(dx1 * dx1 + dy1 * dy1)
+        val dx2 = tx - cx; val dy2 = ty - cy; val d2fac = offsetTo / sqrt(dx2 * dx2 + dy2 * dy2)
+
+        val x1_ = fx + dx1 * d1fac; val y1_ = fy + dy1 * d1fac
+        val x2_ = tx - dx2 * d2fac; val y2_ = ty - dy2 * d2fac
+        val curve = QuadCurve2D.Float(
+            x1_, y1_,
+            cx, cy,
+            x2_, y2_
+        )
+        g2.draw(curve)
+
+        // draw arrowhead at the end of the curve
+        val angle = atan2(y2_ - cy, x2_ - cx)
+        val arrowX1 = x2_ - arrowLen * cos(angle - arrowAngle).toFloat()
+        val arrowY1 = y2_ - arrowLen * sin(angle - arrowAngle).toFloat()
+        val arrowX2 = x2_ - arrowLen * cos(angle + arrowAngle).toFloat()
+        val arrowY2 = y2_ - arrowLen * sin(angle + arrowAngle).toFloat()
+        val arrowHead = Polygon(
+            intArrayOf(x2_.toInt(), arrowX1.toInt(), arrowX2.toInt()),
+            intArrayOf(y2_.toInt(), arrowY1.toInt(), arrowY2.toInt()),
+            3
+        )
+        g2.fill(arrowHead)
+    }
+}
+
+fun <E> defaultEdgeRenderer(): IEdgeRenderer<E> = QuadraticEdge()

src/main/kotlin/com/jaytux/altgraph/swing/DefaultVertexComponent.kt

@@ -0,0 +1,87 @@
+package com.jaytux.altgraph.swing
+
+import com.jaytux.altgraph.layout.PseudoForestLayout
+import java.awt.*
+import java.awt.RenderingHints.KEY_ANTIALIASING
+import java.awt.RenderingHints.VALUE_ANTIALIAS_ON
+import java.awt.geom.AffineTransform
+import java.awt.geom.Ellipse2D
+import javax.swing.JLabel
+
+class DefaultVertexComponent(
+    label: String,
+    private var _shape: Shape = Ellipse2D.Double(0.0, 0.0, 30.0, 30.0),
+    var labelOffset: Point = Point(20, 7),
+) : IDrawable {
+    val label = JLabel(label)
+    private lateinit var _preferredSize: Dimension
+    private var _arrowTarget: Point = Point(0, 0)
+    private var _arrowTargetOffset: Float = 0.0f
+    var fillColor: Color = Color.LIGHT_GRAY
+    var borderStroke: Stroke = BasicStroke(1.0f)
+    var borderColor: Color = Color.BLACK
+
+    var shape: Shape
+        get() = _shape
+        set(value) {
+            _shape = value
+            _arrowTarget = Point(value.bounds.width / 2, value.bounds.height / 2)
+            _arrowTargetOffset = (value.bounds.width + value.bounds.height).toFloat() / 4.0f
+            updatePreferredSize()
+        }
+
+    init {
+        updatePreferredSize()
+        shape = _shape // to initialize arrow target and offset
+    }
+
+    fun updatePreferredSize() {
+        val bounds = shape.bounds
+        val textSize = label.preferredSize
+
+        val cx = bounds.width / 2; val cy = bounds.height / 2
+        val tx = cx + labelOffset.x; val ty = cy + labelOffset.y - textSize.height / 2
+
+        val textRect = Rectangle(tx, ty, textSize.width, textSize.height)
+        val total = bounds.union(textRect)
+        _preferredSize = Dimension(total.width, total.height)
+    }
+
+    override fun draw(graphics: Graphics2D) {
+        val g = graphics.create() as Graphics2D
+        g.setRenderingHint(KEY_ANTIALIASING, VALUE_ANTIALIAS_ON)
+        val shapeBounds = shape.bounds
+        val cx = shapeBounds.width / 2; val cy = shapeBounds.height / 2
+        val tx = AffineTransform.getTranslateInstance((cx - shapeBounds.centerX), (cy - shapeBounds.centerY))
+        val transShape = tx.createTransformedShape(shape)
+
+        g.color = fillColor
+        g.fill(transShape)
+        g.color = borderColor
+        g.stroke = borderStroke
+        g.draw(transShape)
+
+        val textSize = label.preferredSize
+        val lx = cx + labelOffset.x; val ly = cy + labelOffset.y - textSize.height / 2
+        label.size = textSize
+        g.translate(lx, ly)
+        label.paint(g)
+
+        g.dispose()
+    }
+
+    fun vertexSize(): PseudoForestLayout.VertexSize {
+        val size = _preferredSize
+        val lSize = label.preferredSize
+        return PseudoForestLayout.VertexSize(size.graph(), labelOffset.graph(), lSize.graph())
+    }
+
+    fun asRenderData(): IVertexRenderer.RenderData =
+        IVertexRenderer.RenderData(this, _arrowTarget, _arrowTargetOffset)
+}
+
+fun <V> defaultRenderer(
+    toString: (V) -> String = { it.toString() }
+) : IVertexRenderer<V> = IVertexRenderer { v: V ->
+    DefaultVertexComponent(toString(v)).asRenderData()
+}

src/main/kotlin/com/jaytux/altgraph/swing/Functional.kt

@@ -0,0 +1,21 @@
+package com.jaytux.altgraph.swing
+
+import java.awt.Graphics2D
+import java.awt.Point
+
+interface IDrawable {
+    fun draw(graphics: Graphics2D)
+}
+
+fun interface IVertexRenderer<V> {
+    data class RenderData(
+        val drawer: IDrawable,
+        val arrowTarget: Point,
+        val arrowTargetOffset: Float
+    )
+    fun getDrawable(v: V): RenderData
+}
+
+fun interface IEdgeRenderer<E> {
+    fun drawEdge(g: Graphics2D, from: Point, to: Point, meta: E, offsetFrom: Float, offsetTo: Float)
+}

src/main/kotlin/com/jaytux/altgraph/swing/GeometryWrappers.kt

@@ -1,29 +1,12 @@
 package com.jaytux.altgraph.swing
 
-import com.jaytux.altgraph.layout.IPoint
-import com.jaytux.altgraph.layout.ISize
+import com.jaytux.altgraph.layout.GPoint
+import com.jaytux.altgraph.layout.GSize
 import java.awt.Dimension
 import java.awt.Point
 
-class GSize(val size: Dimension) : ISize<GSize> {
-    override fun width(): Float = size.width.toFloat()
-    override fun height(): Float = size.height.toFloat()
-    override fun copy(width: Float, height: Float): GSize =
-        GSize(Dimension(width.toInt(), height.toInt()))
+fun GSize.swing() = Dimension(width.toInt(), height.toInt())
+fun GPoint.swing() = Point(x.toInt(), y.toInt())
 
-    override fun hashCode(): Int = size.hashCode()
-    override fun equals(other: Any?): Boolean = other is GSize && size == other.size
-    override fun toString(): String = "$size"
-}
-
-class GPoint(val point: Point) : IPoint<GPoint> {
-    override fun x(): Float = point.x.toFloat()
-    override fun y(): Float = point.y.toFloat()
-    override fun copy(x: Float, y: Float): GPoint =
-        GPoint(Point(x.toInt(), y.toInt()))
-
-    override fun hashCode(): Int = point.hashCode()
-    override fun equals(other: Any?): Boolean =
-        other is GPoint && point == other.point
-    override fun toString(): String = "$point"
-}
+fun Dimension.graph() = GSize(width.toFloat(), height.toFloat())
+fun Point.graph() = GPoint(x.toFloat(), y.toFloat())

src/main/kotlin/com/jaytux/altgraph/swing/GraphPane.kt

@@ -0,0 +1,131 @@
+package com.jaytux.altgraph.swing
+
+import com.jaytux.altgraph.core.IGraph
+import com.jaytux.altgraph.layout.ILayout
+import java.awt.Graphics
+import java.awt.Graphics2D
+import java.awt.Point
+import java.awt.event.MouseEvent
+import java.awt.event.MouseMotionListener
+import java.awt.geom.AffineTransform
+import javax.swing.JPanel
+
+class GraphPane<V, E>(
+    val graph: IGraph<V, E>,
+    layout: (GraphPane<V, E>, IGraph<V, E>) -> ILayout<V, E>
+) : JPanel()
+{
+    private val _delta = AffineTransform()
+    private var _zoom = 1.0
+    private var _panX = 0.0
+    private var _panY = 0.0
+
+    private val _layout: ILayout<V, E>
+    private var _renderer: IVertexRenderer<V> = defaultRenderer()
+    private var _edgeRenderer: IEdgeRenderer<E> = defaultEdgeRenderer()
+    private val _vertices = mutableMapOf<V, IVertexRenderer.RenderData>()
+
+    init {
+        this.layout = null
+        _delta.setToIdentity()
+        _layout = layout(this, graph)
+
+        addMouseWheelListener { event ->
+            val delta = event.preciseWheelRotation
+            if(delta < 0) {
+                _zoom *= 1.1
+            } else {
+                _zoom /= 1.1
+            }
+            transform()
+        }
+
+        addMouseMotionListener(object : MouseMotionListener {
+            var last: Point? = null
+
+            override fun mouseDragged(e: MouseEvent?) {
+                e?.let {
+                    last?.let {
+                        val dx = e.x - it.x
+                        val dy = e.y - it.y
+                        _panX += dx
+                        _panY += dy
+                        transform()
+                    }
+
+                    last = Point(e.x, e.y)
+                }
+            }
+
+            override fun mouseMoved(e: MouseEvent?) {
+                e?.let { last = it.point }
+            }
+        })
+    }
+
+    private fun transform() {
+        _delta.setToIdentity()
+        _delta.translate(_panX, _panY)
+        _delta.scale(_zoom, _zoom)
+        repaint()
+    }
+
+    fun relayout() {
+        _layout.compute()
+        repaint()
+    }
+
+    fun getComponentFor(v: V): IDrawable =
+        getRenderDataFor(v).drawer
+
+    fun getRenderDataFor(v: V): IVertexRenderer.RenderData =
+        _vertices.getOrPut(v) { _renderer.getDrawable(v) }
+
+    fun setRenderer(renderer: IVertexRenderer<V>) {
+        _renderer = renderer
+        _vertices.clear()
+        repaint()
+    }
+
+    fun setEdgeRenderer(renderer: IEdgeRenderer<E>) {
+        _edgeRenderer = renderer
+        repaint()
+    }
+
+    fun resetComponents() {
+        _vertices.clear()
+        repaint()
+    }
+
+    override fun paintComponent(g: Graphics?) {
+        super.paintComponent(g)
+        if(g == null) return
+
+        val g2 = g.create() as Graphics2D
+        g2.transform = _delta
+        graph.vertices().forEach { v -> getRenderDataFor(v) } // ensure all vertices are rendered
+        _vertices.forEach { (v, c) ->
+            if(v !in graph.vertices()) return@forEach
+            val pos = _layout.location(v).swing()
+
+            val g3 = g2.create() as Graphics2D
+            g3.translate(pos.x, pos.y)
+            c.drawer.draw(g3)
+            g3.dispose()
+        }
+
+        graph.edges().forEach { (e, vv) ->
+            val first = getRenderDataFor(vv.first)
+            val second = getRenderDataFor(vv.second)
+            val from = _layout.location(vv.first) + first.arrowTarget.graph()
+            val to = _layout.location(vv.second) + second.arrowTarget.graph()
+
+            _edgeRenderer.drawEdge(g2,
+                from.swing(),
+                to.swing(),
+            e, first.arrowTargetOffset, second.arrowTargetOffset)
+        }
+
+        g2.dispose()
+    }
+}