Remove GC allocations on preview property collection

com.unity.shadergraph/Editor/Data/Graphs/BooleanMaterialSlot.cs

         public override SlotValueType valueType { get { return SlotValueType.Boolean; } }
         public override ConcreteSlotValueType concreteValueType { get { return ConcreteSlotValueType.Boolean; } }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override void CopyValuesFrom(MaterialSlot foundSlot)

com.unity.shadergraph/Editor/Data/Graphs/ColorMaterialSlot.cs

             properties.AddShaderProperty(property);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/ColorRGBMaterialSlot.cs

             properties.AddShaderProperty(property);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
     }
 }

com.unity.shadergraph/Editor/Data/Graphs/CubemapInputMaterialSlot.cs

             properties.AddShaderProperty(prop);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override void CopyValuesFrom(MaterialSlot foundSlot)

com.unity.shadergraph/Editor/Data/Graphs/DynamicValueMaterialSlot.cs

 			m_ConcreteValueType = valueType;
 		}
 
-		public override List<PreviewProperty> GetPreviewProperties(string name)
+		public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
             var propType = ConvertConcreteSlotValueTypeToPropertyType(concreteValueType);
 			var pp = new PreviewProperty(propType) { name = name };
 			if (propType == PropertyType.Vector1)
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
 		protected override string ConcreteSlotValueAsVariable(AbstractMaterialNode.OutputPrecision precision)

com.unity.shadergraph/Editor/Data/Graphs/DynamicVectorMaterialSlot.cs

             m_ConcreteValueType = valueType;
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public virtual void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
             var propType = ConvertConcreteSlotValueTypeToPropertyType(concreteValueType);
             var pp = new PreviewProperty(propType) { name = name };
             if (propType == PropertyType.Vector1)
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         protected override string ConcreteSlotValueAsVariable(AbstractMaterialNode.OutputPrecision precision)

com.unity.shadergraph/Editor/Data/Graphs/GradientInputMaterialSlot.cs

             properties.AddShaderProperty(prop);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(new PreviewProperty(PropertyType.Vector1)
+            properties.Add(new PreviewProperty(PropertyType.Vector1)
-            props.Add(new PreviewProperty(PropertyType.Vector1)
+            properties.Add(new PreviewProperty(PropertyType.Vector1)
-            props.Add(new PreviewProperty(PropertyType.Vector1)
+            properties.Add(new PreviewProperty(PropertyType.Vector1)
             {
                 name = string.Format("{0}_AlphasLength", name),
                 floatValue = value.alphaKeys.Length
             {
-                props.Add(new PreviewProperty(PropertyType.Vector4)
+                properties.Add(new PreviewProperty(PropertyType.Vector4)
                 {
                     name = string.Format("{0}_ColorKey{1}", name, i),
                     vector4Value = i < value.colorKeys.Length ? GradientUtils.ColorKeyToVector(value.colorKeys[i]) : Vector4.zero
             for(int i = 0; i < 8; i++)
             {
-                props.Add(new PreviewProperty(PropertyType.Vector2)
+                properties.Add(new PreviewProperty(PropertyType.Vector2)
-            return props;
         }
 
         public override void CopyValuesFrom(MaterialSlot foundSlot)

com.unity.shadergraph/Editor/Data/Graphs/MaterialSlot.cs

             }
         }
 
-        public virtual List<PreviewProperty> GetPreviewProperties(string name)
+        public virtual void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(default(PreviewProperty));
-            return props;
+            properties.Add(default(PreviewProperty));
         }
 
         public abstract void CopyValuesFrom(MaterialSlot foundSlot);

com.unity.shadergraph/Editor/Data/Graphs/Matrix2MaterialSlot.cs

             properties.AddShaderProperty(property);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override SlotValueType valueType { get { return SlotValueType.Matrix2; } }

com.unity.shadergraph/Editor/Data/Graphs/Matrix3MaterialSlot.cs

             properties.AddShaderProperty(property);
         }
         
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override SlotValueType valueType { get { return SlotValueType.Matrix3; } }

com.unity.shadergraph/Editor/Data/Graphs/Matrix4MaterialSlot.cs

             properties.AddShaderProperty(property);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override SlotValueType valueType { get { return SlotValueType.Matrix4; } }

com.unity.shadergraph/Editor/Data/Graphs/Texture2DInputMaterialSlot.cs

             properties.AddShaderProperty(prop);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override void CopyValuesFrom(MaterialSlot foundSlot)

com.unity.shadergraph/Editor/Data/Graphs/Vector1MaterialSlot.cs

         public override SlotValueType valueType { get { return SlotValueType.Vector1; } }
         public override ConcreteSlotValueType concreteValueType { get { return ConcreteSlotValueType.Vector1; } }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override void CopyValuesFrom(MaterialSlot foundSlot)

com.unity.shadergraph/Editor/Data/Graphs/Vector2MaterialSlot.cs

             properties.AddShaderProperty(property);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override SlotValueType valueType { get { return SlotValueType.Vector2; } }

com.unity.shadergraph/Editor/Data/Graphs/Vector3MaterialSlot.cs

             properties.AddShaderProperty(property);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override SlotValueType valueType { get { return SlotValueType.Vector3; } }

com.unity.shadergraph/Editor/Data/Graphs/Vector4MaterialSlot.cs

             properties.AddShaderProperty(property);
         }
 
-        public override List<PreviewProperty> GetPreviewProperties(string name)
+        public override void GetPreviewProperties(List<PreviewProperty> properties, string name)
-            List<PreviewProperty> props = new List<PreviewProperty>();
-            props.Add(pp);
-            return props;
+            properties.Add(pp);
         }
 
         public override SlotValueType valueType { get { return SlotValueType.Vector4; } }

com.unity.shadergraph/Editor/Data/Nodes/AbstractMaterialNode.cs

                 if (s_TempEdges.Any())
                     continue;
 
-                var items = s.GetPreviewProperties(GetVariableNameForSlot(s.id));
-                for(int i = 0; i < items.Count; i++)
+                s.GetPreviewProperties(properties, GetVariableNameForSlot(s.id));
+                for(int i = 0; i < properties.Count; i++)
-                    if (items[i].name == null)
-                    continue;
-
-                    properties.Add(items[i]);
+                    if (properties[i].name == null)
+                        properties.Remove(properties[i]);
                 }
             }
         }