Require opt-in attribute to reset combinator

Bonsai.Core/Expressions/CombinatorBuilder.cs

@@ -77,6 +77,11 @@ void UpdateArgumentRange()
 
         static Delegate BuildResetCombinator(Type combinatorType)
         {
+            if (!combinatorType.IsDefined(typeof(ResetCombinatorAttribute)))
+            {
+                return null;
+            }
+
             List<PropertyInfo> resetProperties = null;
             var combinatorProperties = combinatorType.GetProperties();
             for (int i = 0; i < combinatorProperties.Length; i++)

Bonsai.Core/ResetCombinatorAttribute.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Bonsai
+{
+    /// <summary>
+    /// Instructs the build process to reset non-serializable public properties
+    /// marked with <see cref="System.Xml.Serialization.XmlIgnoreAttribute"/>.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class)]
+    public sealed class ResetCombinatorAttribute : Attribute
+    {
+    }
+}

Bonsai.Vision/Drawing/AddImage.cs

@@ -8,6 +8,7 @@ namespace Bonsai.Vision.Drawing
     /// <summary>
     /// Represents an operator that specifies drawing the specified image to the canvas.
     /// </summary>
+    [ResetCombinator]
     [Description("Draws the specified image to the canvas.")]
     public class AddImage : CanvasElement
     {

Bonsai.Vision/Drawing/DrawContours.cs

@@ -9,6 +9,7 @@ namespace Bonsai.Vision.Drawing
     /// Represents an operator that specifies drawing contour outlines or filled
     /// interiors in an image.
     /// </summary>
+    [ResetCombinator]
     [Description("Draws contour outlines or filled interiors in an image.")]
     public class DrawContours : CanvasElement
     {

Bonsai.Vision/Drawing/FillPolygon.cs

@@ -9,6 +9,7 @@ namespace Bonsai.Vision.Drawing
     /// Represents an operator that specifies filling an area bounded by several
     /// polygonal contours.
     /// </summary>
+    [ResetCombinator]
     [Description("Fills an area bounded by several polygonal contours.")]
     public class FillPolygon : CanvasElement
     {

Bonsai.Vision/Drawing/LineChart.cs

@@ -9,6 +9,7 @@ namespace Bonsai.Vision.Drawing
     /// Represents an operator that specifies drawing a line chart by plotting
     /// each row of a matrix as a polyline element.
     /// </summary>
+    [ResetCombinator]
     [Description("Draws a line chart by plotting each row of a matrix as a polyline element.")]
     public class LineChart : CanvasElement
     {

Bonsai.Vision/Drawing/Path.cs

@@ -9,6 +9,7 @@ namespace Bonsai.Vision.Drawing
     /// <summary>
     /// Represents an operator that specifies drawing a path from an array of vertices.
     /// </summary>
+    [ResetCombinator]
     [Description("Draws a path from an array of vertices.")]
     public class Path : CanvasElement
     {

Bonsai.Vision/Drawing/PolyLine.cs

@@ -8,6 +8,7 @@ namespace Bonsai.Vision.Drawing
     /// <summary>
     /// Represents an operator that specifies drawing one or more polygonal curves.
     /// </summary>
+    [ResetCombinator]
     [Description("Draws one or more polygonal curves.")]
     public class PolyLine : CanvasElement
     {