Remove needless pointer offsets from generated C#

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/AST/ClassLayout.cs

@@ -171,6 +171,11 @@ namespace CppSharp.AST
             }
         }
 
+        /// <summary>
+        /// Indicates whether this class layout has a subclass at a non-zero offset.
+        /// </summary>
+        public bool HasSubclassAtNonZeroOffset { get; set; }
+
         private List<LayoutField> vTablePointers;
     }
 }

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -428,7 +428,8 @@ namespace CppSharp.Generators.CSharp
 
                     PushBlock(BlockKind.Field);
 
-                    WriteLine("protected int {0};", Helpers.PointerAdjustmentIdentifier);
+                    if (@class.Layout.HasSubclassAtNonZeroOffset)
+                        WriteLine($"protected int {Helpers.PrimaryBaseOffsetIdentifier};");
 
                     // use interfaces if any - derived types with a secondary base this class must be compatible with the map
                     var @interface = @class.Namespace.Classes.FirstOrDefault(
@@ -2183,8 +2184,8 @@ namespace CppSharp.Generators.CSharp
 
             if (@class.IsRefType)
             {
-                if (@class.HasBaseClass)
-                    WriteLine("{0} = {1};", Helpers.PointerAdjustmentIdentifier,
+                if (@class.BaseClass?.Layout.HasSubclassAtNonZeroOffset == true)
+                    WriteLine("{0} = {1};", Helpers.PrimaryBaseOffsetIdentifier,
                         GetOffsetToBase(@class, @class.BaseClass));
                 if (!@class.IsAbstractImpl)
                 {
@@ -2945,17 +2946,17 @@ namespace CppSharp.Generators.CSharp
                 to = to.OriginalClass ?? to;
                 baseOffset = GetOffsetToBase(from, to);
             }
-            var isPrimaryBase = (from.BaseClass?.OriginalClass ?? from.BaseClass) == to;
-            if (isPrimaryBase)
+            bool isPrimaryBase = (from.BaseClass?.OriginalClass ?? from.BaseClass) == to;
+            bool isOrHasSubclassAtNonZeroOffset =
+                from.Layout.HasSubclassAtNonZeroOffset ||
+                to?.Layout.HasSubclassAtNonZeroOffset == true;
+            if (isPrimaryBase && isOrHasSubclassAtNonZeroOffset)
             {
-                return string.Format("({0} + {1}{2})",
-                    Helpers.InstanceIdentifier,
-                    Helpers.PointerAdjustmentIdentifier,
-                    baseOffset == 0 ? string.Empty : (" - " + baseOffset));
+                return Helpers.InstanceIdentifier +
+                    (baseOffset == 0 ? " + " + Helpers.PrimaryBaseOffsetIdentifier : string.Empty);
             }
-            return string.Format("({0}{1})",
-                Helpers.InstanceIdentifier,
-                baseOffset == 0 ? string.Empty : " + " + baseOffset);
+            return Helpers.InstanceIdentifier +
+                (baseOffset == 0 ? string.Empty : " + " + baseOffset);
         }
 
         private static uint GetOffsetToBase(Class from, Class to)

src/Generator/Generators/CodeGenerator.cs

@@ -1209,7 +1209,7 @@ namespace CppSharp.Generators
         public static readonly string InternalStruct = Generator.GeneratedIdentifier("Internal");
         public static readonly string InstanceField = Generator.GeneratedIdentifier("instance");
         public static readonly string InstanceIdentifier = Generator.GeneratedIdentifier("Instance");
-        public static readonly string PointerAdjustmentIdentifier = Generator.GeneratedIdentifier("PointerAdjustment");
+        public static readonly string PrimaryBaseOffsetIdentifier = Generator.GeneratedIdentifier("PrimaryBaseOffset");
         public static readonly string ReturnIdentifier = Generator.GeneratedIdentifier("ret");
         public static readonly string DummyIdentifier = Generator.GeneratedIdentifier("dummy");
         public static readonly string TargetIdentifier = Generator.GeneratedIdentifier("target");

src/Parser/ASTConverter.cs

@@ -1587,7 +1587,15 @@ namespace CppSharp
             _class.IsInjected = @class.IsInjected;
 
             if (@class.Layout != null)
+            {
                 _class.Layout = VisitClassLayout(@class.Layout);
+                if (_class.BaseClass != null)
+                {
+                    AST.LayoutBase @base = _class.Layout.Bases.Find(
+                        b => b.Class == _class.BaseClass);
+                    _class.BaseClass.Layout.HasSubclassAtNonZeroOffset = @base.Offset > 0;
+                }
+            }
         }
 
         public override AST.Declaration VisitClass(Class @class)