Fix drag freezing

Author: li3zhen1

Examples/ForceDirectedGraphExample/ForceDirectedGraphExample/Lattice.swift

@@ -11,7 +11,7 @@ import Grape
 
 struct Lattice: View {
 
-    let width = 20
+    let width = 30
     let edge: [(Int, Int)]
 
     @State var graphStates = ForceDirectedGraphState(
@@ -33,7 +33,6 @@ struct Lattice: View {
         self.edge = edge
     }
 
-    @inlinable
     var body: some View {
         ForceDirectedGraph(states: graphStates) {
 
@@ -51,11 +50,15 @@ struct Lattice: View {
 
         } force: {
             .link(
-                originalLength: .constant(0.8),
+                originalLength: 0.8,
                 stiffness: .weightedByDegree { _, _ in 1.0 }
             )
             .manyBody(strength: -0.8)
         }
+        .graphOverlay(content: { proxy in
+            Rectangle().fill(.clear).contentShape(Rectangle())
+                .withGraphDragGesture(proxy)
+        })
         .toolbar {
             GraphStateToggle(graphStates: graphStates)
         }

Examples/ForceDirectedGraphExample/ForceDirectedGraphExample/MermaidVisualization.swift

@@ -100,7 +100,7 @@ struct MermaidVisualization: View {
 
         } force: {
             .manyBody()
-            .link(originalLength: .constant(70))
+            .link(originalLength: 70.0)
             .center()
         } emittingNewNodesWithStates: { id in
             KineticState(position: getInitialPosition(id: id, r: 100))
@@ -111,7 +111,6 @@ struct MermaidVisualization: View {
                 .onTapGesture { value in
                     if let nodeID = proxy.locateNode(at: .init(x: value.x, y: value.y)) {
                         guard let nodeID = nodeID as? String else { return }
-                        print(nodeID)
                         model.tappedNode = nodeID
                     }
                 }

Examples/ForceDirectedGraphExample/ForceDirectedGraphExample/Miserables.swift

@@ -69,7 +69,7 @@ struct MiserableGraph: View {
             .manyBody(strength: -20)
             .center()
             .link(
-                originalLength: .constant(35.0),
+                originalLength: 35.0,
                 stiffness: .weightedByDegree { _, _ in 1.0}
             )
         }

Examples/ForceDirectedGraphExample/ForceDirectedGraphExample/MyRing.swift

@@ -14,43 +14,44 @@ struct MyRing: View {
 
     @State var graphStates = ForceDirectedGraphState()
 
+    @State var draggingNodeID: Int? = nil
+    
+    static let storkeStyle = StrokeStyle(lineWidth: 1.5, lineCap: .round, lineJoin: .round)
+    
     var body: some View {
 
         ForceDirectedGraph(states: graphStates) {
             Series(0..<20) { i in
+                
                 NodeMark(id: 3 * i + 0)
                     .symbolSize(radius: 6.0)
                     .foregroundStyle(.green)
-                    .stroke(.clear)
+                    .stroke(3*i+0 == draggingNodeID ? .black : .clear, Self.storkeStyle)
+                    
                 NodeMark(id: 3 * i + 1)
                     .symbol(.pentagon)
                     .symbolSize(radius:10)
                     .foregroundStyle(.blue)
-                    .stroke(.clear)
+                    .stroke(3*i+1 == draggingNodeID ? .black : .clear, Self.storkeStyle)
+                
                 NodeMark(id: 3 * i + 2)
                     .symbol(.circle)
                     .symbolSize(radius:6.0)
                     .foregroundStyle(.yellow)
-                    .stroke(.clear)
+                    .stroke(3*i+2 == draggingNodeID ? .black : .clear, Self.storkeStyle)
 
                 LinkMark(from: 3 * i + 0, to: 3 * i + 1)
                 LinkMark(from: 3 * i + 1, to: 3 * i + 2)
-                
                 LinkMark(from: 3 * i + 0, to: 3 * ((i + 1) % 20) + 0)
                 LinkMark(from: 3 * i + 1, to: 3 * ((i + 1) % 20) + 1)
                 LinkMark(from: 3 * i + 2, to: 3 * ((i + 1) % 20) + 2)
-                
-                
             }
-            .stroke(
-                .black,
-                StrokeStyle(lineWidth: 1.5, lineCap: .round, lineJoin: .round)
-            )
+            .stroke(.black, Self.storkeStyle)
 
         } force: {
             .manyBody(strength: -15)
             .link(
-                originalLength: .constant(20.0),
+                originalLength: 20.0,
                 stiffness: .weightedByDegree { _, _ in 3.0}
             )
             .center()
@@ -69,10 +70,16 @@ struct MyRing: View {
     func describe(_ state: GraphDragState?) {
         switch state {
         case .node(let anyHashable):
-            print("Dragging \(anyHashable as! Int)")
+            let id = anyHashable as! Int
+            if draggingNodeID != id {
+                draggingNodeID = id
+                print("Dragging \(id)")
+            }
         case .background(let start):
+            draggingNodeID = nil
             print("Dragging \(start)")
         case nil:
+            draggingNodeID = nil
             print("Drag ended")
         }
     }

Sources/Grape/Descriptors/ForceDescriptor.swift

@@ -6,6 +6,13 @@ public enum NodeAttribute<NodeID: Hashable, Attribute> {
     case constant(Attribute)
 }
 
+extension NodeAttribute: ExpressibleByFloatLiteral where Attribute == Double {
+    @inlinable
+    public init(floatLiteral value: Double) {
+        self = .constant(value)
+    }
+}
+
 extension NodeAttribute {
     @inlinable
     func makeCompactRepresentation(nodeIDs: [NodeID]) -> ForceSimulation.AttributeDescriptor<Attribute> {
@@ -270,14 +277,26 @@ public struct ManyBodyForce<NodeID: Hashable>: _ForceDescriptor {
 
 public struct LinkForce<NodeID: Hashable>: _ForceDescriptor {
 
-    public enum Stiffness {
+    public enum Stiffness: ExpressibleByFloatLiteral {
         case constant(Double)
         case weightedByDegree((EdgeID<NodeID>, LinkLookup<NodeID>) -> Double)
+        
+        @inlinable
+        public init(floatLiteral value: Double) {
+            self = .weightedByDegree({ _, _ in
+                value
+            })
+        }
     }
 
-    public enum LinkLength {
+    public enum LinkLength: ExpressibleByFloatLiteral {
         case constant(Double)
         case varied((EdgeID<NodeID>, LinkLookup<NodeID>) -> Double)
+        
+        @inlinable
+        public init(floatLiteral value: Double) {
+            self = .constant(value)
+        }
     }
     public var stiffness: Stiffness
     public var originalLength: LinkLength

Sources/Grape/Gestures/GraphDragGesture.swift

@@ -81,6 +81,7 @@ struct GraphDragModifier: ViewModifier {
         if dragState == nil {
             if let nodeID = graphProxy.locateNode(at: value.startLocation) {
                 dragState = .node(nodeID)
+                
                 graphProxy.setNodeFixation(nodeID: nodeID, fixation: value.startLocation)
             } else {
                 dragState = .background(start: value.location.simd)

Sources/Grape/Modifiers/GraphProxy.swift

@@ -26,8 +26,8 @@ extension GraphProxy: _AnyGraphProxyProtocol {
     }
 
     @inlinable
-    public func setNodeFixation(nodeID: some Hashable, fixation: CGPoint?) {
-        storage?.setNodeFixation(nodeID: nodeID, fixation: fixation)
+    public func setNodeFixation(nodeID: some Hashable, fixation: CGPoint?, minimumAlpha: Double = 0.5) {
+        storage?.setNodeFixation(nodeID: nodeID, fixation: fixation, minimumAlpha: minimumAlpha)
     }
 
     @inlinable

Sources/Grape/Views/ForceDirectedGraphModel.swift

@@ -9,7 +9,7 @@ public protocol _AnyGraphProxyProtocol {
     func locateNode(at locationInViewportCoordinate: CGPoint) -> AnyHashable?
 
     @inlinable
-    func setNodeFixation(nodeID: some Hashable, fixation: CGPoint?)
+    func setNodeFixation(nodeID: some Hashable, fixation: CGPoint?, minimumAlpha: Double)
 
     @inlinable
     var kineticAlpha: Double { get nonmutating set }
@@ -38,10 +38,16 @@ extension ForceDirectedGraphModel: _AnyGraphProxyProtocol {
     }
 
     @inlinable
-    public func setNodeFixation(nodeID: some Hashable, fixation: CGPoint?) {
+    public func setNodeFixation(nodeID: some Hashable, fixation: CGPoint?, minimumAlpha: Double) {
         guard let nodeID = nodeID as? NodeID else {
             return
         }
+
+        simulationContext.storage.kinetics.alpha = max(
+            simulationContext.storage.kinetics.alpha, 
+            minimumAlpha
+        )
+
         let newLocationInSimulation: SIMD2<Double>? =
             if let fixation {
                 finalTransform.invert(fixation.simd)
@@ -58,8 +64,8 @@ extension ForceDirectedGraphModel: _AnyGraphProxyProtocol {
         get {
             simulationContext.storage.kinetics.alpha
         }
-        set {
-            simulationContext.storage.kinetics.alpha = newValue
+        _modify {
+            yield &simulationContext.storage.kinetics.alpha
         }
     }
 }
@@ -720,7 +726,7 @@ extension ForceDirectedGraphModel {
                 count: self.simulationContext.storage.kinetics.position.count
             )
         }
-        debugPrint("[REVIVED]")
+        debugPrint("Graph state revived. Note this might cause expensive rerendering when combined with `richLabel` with unstable id.")
     }
 
 }