Fix error amd Update features.

Changed Span<PointData> to ReadOnlySpan<PointData> on method Operate in EffectorBase.cs
Changed the return type of method Operate in EffectorBase.cs from void to PointDate
Added FieldHelper and BlendField function to make the blending work.

Runtime/Cloner/Helper/FieldHelper.cs

@@ -0,0 +1,56 @@
+using Unity.Mathematics;
+
+namespace Misaki.ArtTool
+{
+    internal class FieldHelper
+    {
+        public static float BlendField(float a, float b, float t, BlendingMode blendingMode)
+        {
+            var result = 0.0f;
+            switch (blendingMode)
+            {
+                case BlendingMode.Normal:
+                    result = math.lerp(a, b, t);
+                    break;
+
+                case BlendingMode.Min:
+                    result = math.lerp(a, math.min(a, b), t);
+                    break;
+
+                case BlendingMode.Subtract:
+                    result = math.lerp(a, a - b, t);
+                    break;
+
+                case BlendingMode.Multiply:
+                    result = math.lerp(a, a * b, t);
+                    break;
+
+                case BlendingMode.Overlay:
+                    var o1 = 1.0f - 2.0f * (1.0f - a) * (1.0f - b);
+                    var o2 = 2.0f * a * b;
+                    var zeroOrOne = math.step(a, 0.5f);
+                    result = o2 * zeroOrOne + (1.0f - zeroOrOne) * o1;
+                    result = math.lerp(a, result, t);
+                    break;
+
+                case BlendingMode.Max:
+                    result = math.lerp(a, math.max(a, b), t);
+                    break;
+
+                case BlendingMode.Add:
+                    result = math.lerp(a, a + b, t);
+                    break;
+
+                case BlendingMode.Screen:
+                    result = 1.0f - (1.0f - b) * (1.0f - a);
+                    result = math.lerp(a, result, t);
+                    break;
+
+                default:
+                    break;
+            }
+
+            return result;
+        }
+    }
+}