More work on radial menus

Source/Integration/RadialMenu.cpp

@@ -0,0 +1,86 @@
+#include "RadialMenu.h"
+
+
+void URadialMenu::Configure(int32 NItems, float ItemHeight, float InnerRadius, float MinSpoke, float Spread)
+{
+    CNItems = NItems;
+    CItemHeight = ItemHeight;
+    CInnerRadius = InnerRadius;
+    CMinSpoke = MinSpoke;
+    CSpread = Spread;
+
+    CNumRight = (NItems / 2);
+    CNumLeft = NItems - CNumRight;
+    Items.SetNum(NItems);
+
+    LeftItems = View(Items.GetData(), CNumLeft);
+    RightItems = View(Items.GetData() + CNumLeft, CNumRight);
+
+    CalculateSide(LeftItems);
+    CalculateSide(RightItems);
+    FlipHorizontal(LeftItems);
+}
+
+FVector2D URadialMenu::PieSliceToVector(double Slice, double Slices)
+{
+    double HalfRevolutions = (Slice + 0.5) / Slices;
+    double Radians = (HalfRevolutions * UE_PI);
+    return FVector2D(FMath::Sin(Radians), -FMath::Cos(Radians));
+}
+
+void URadialMenu::FlipHorizontal(View V)
+{
+    for (FRadialMenuItem& Item : V)
+    {
+        Item.Point1.X = -Item.Point1.X;
+        Item.Point2.X = -Item.Point2.X;
+        Item.Point3.X = -Item.Point3.X;
+        Item.RightSide = !Item.RightSide;
+    }
+}
+
+void URadialMenu::CalculateSide(View V)
+{
+    // Point1 is simple. RightSide is always initialized to
+    // true, it may get reversed in FlipHorizontal.
+    for (int32 I = 0; I < V.Num(); I++)
+    {
+        V[I].RightSide = true;
+        V[I].Point1 = PieSliceToVector(I, V.Num()) * CInnerRadius;
+    }
+
+    // Calculate point2 for all spokes.
+    double NextLineMin = CItemHeight * 0.5;
+    int32 Mid = (V.Num() / 2);
+    if (V.Num() & 1)
+    {
+        V[Mid].Point2 = FVector2D(CInnerRadius + CMinSpoke, 0.0);
+        NextLineMin = CItemHeight;
+        Mid += 1;
+    }
+    for (int32 I = Mid; I < V.Num(); I++)
+    {
+        FVector2D UnitVec = PieSliceToVector(I, V.Num());
+        double Y = (UnitVec.Y * (CInnerRadius + CMinSpoke));
+        if (Y < NextLineMin) Y = NextLineMin;
+        NextLineMin = Y + CItemHeight;
+        FVector2D Point2 = UnitVec * (Y / UnitVec.Y);
+        V[I].Point2 = Point2;
+        V[V.Num() - I].Point2 = Point2 * FVector2D(1.0,-1.0);
+    }
+
+    // The rule we use for calculating point2 may result in
+    // a very short horizontal spoke.  If so, fix it.
+    if ((V.Num() & 1) && (V.Num() >= 3))
+    {
+        Mid = V.Num() / 2;
+        if (V[Mid].Point2.X < V[Mid + 1].Point2.X)
+            V[Mid].Point2.X = V[Mid + 1].Point2.X;
+    }
+
+    // Calculate Point3.
+    for (int32 I = 0; I < V.Num(); I++)
+    {
+        V[I].Point3 = V[I].Point2 + FVector2D(CSpread, 0.0);
+    }
+}

Source/Integration/RadialMenu.h

@@ -0,0 +1,60 @@
+//
+// This class implements the layout calculatations for a radial
+// menu.
+//
+
+#pragma once
+
+#include "CoreMinimal.h"
+#include "RadialMenu.generated.h"
+
+
+USTRUCT(BlueprintType)
+struct FRadialMenuItem
+{
+    GENERATED_BODY()
+
+    FVector2D Point1 = {0,0};
+    FVector2D Point2 = {0,0};
+    FVector2D Point3 = {0,0};
+    bool RightSide = false;
+};
+
+UCLASS(BlueprintType)
+class URadialMenu : public UObject
+{
+    GENERATED_BODY()
+
+public:
+    UFUNCTION(BlueprintCallable)
+    void Configure(int32 NItems, float ItemHeight, float InnerRadius, float MinSpoke, float Spread);
+
+    UFUNCTION(BlueprintCallable)
+    int32 NumItems() const { return Items.Num(); }
+
+    UFUNCTION(BlueprintCallable)
+    const TArray<FRadialMenuItem> GetItems() const { return Items; }
+
+    TArray<FRadialMenuItem> Items;
+
+private:
+    using View = TArrayView<FRadialMenuItem>;
+
+    void CalculateSide(View V);
+    void FlipHorizontal(View V);
+
+    // The half-circle is divided into pie slices.  Returns a direction vector
+    // which aims directly down the center of the pie slice.
+    FVector2D PieSliceToVector(double Slice, double Slices);
+    
+    int32 CNItems = 0;
+    float CItemHeight = 0;
+    float CInnerRadius = 0;
+    float CMinSpoke = 0;
+    float CSpread = 0;
+    int32 CNumLeft = 0;
+    int32 CNumRight = 0;
+    View LeftItems;
+    View RightItems;
+};
+