This document discusses calling C++ code from C# and summarizes the UrhoSharp library which provides bindings between the C++ Urho3D game engine and C#. Key points: - C++/CLI, COM, and P/Invoke can be used to call C++ from C# - UrhoSharp exposes over 200 classes and 5000 methods of the Urho3D API to C# with similar performance - The binding is generated automatically from Urho3D header and source files using a custom binding generator - Object lifetime is managed by reference counting between the managed and native memory arenas

1. C++ via C#
Egor Bogatov
@EgorBo

2. Calling C++ from C#. For what?
• Lovely IDE + R#
• Syntactic sugar
• nuget

3. Calling C++ from C#. How?
• C++/CLI
• COM
• [DllImport], [MethodImpl]
• IPC, Sockets,…

4. Calling C++ from C#. How?
• C++/CLI
• COM
• [DllImport], [MethodImpl]
• IPC, Sockets,…

5. UrhoSharp
• ~ 200 classes
• ~ 5000 methods
• Same FPS
• +10% memory
• C# for:
Windows
Mac OS
Android
iOS
tvOS

6. Urho3D API
class Node : public Animatable
{
public:
Node(Context* context);
void SetName(const String& name);
const String& GetName();
void SetPosition(const Vector3& position);
const Vector3& GetPosition();
void AddChild(Node* node, unsigned index = M_MAX_UNSIGNED);
void RemoveChild(Node* node);
};
public class Node : Animatable
{
public Node(Context context) { }
public string Name { get; set; }
public Vector3 Position { get; set; }
void AddChild(Node node, uint index = uint.MaxValue) { }
void RemoveChild(Node node) { }
}
Node.cpp
C++
C#

7. Urho3D API
class Node : public Animatable
{
public:
Node(Context* context);
void SetName(const String& name);
};
glue.cpp

8. Urho3D API
Node.cpp
C#
Node node = new Node(context);
node.SetName("foo");
Node* node = new Node(context_);
node->SetName("foo");

9. Urho3D APIvoid SetName(const String& name);
extern "C"
DllExport void Node_SetName (Node *target, const char * name){
target->SetName (Urho3D::String(name));
}
[DllImport ("mono-urho", …)]
static extern void Node_SetName (IntPtr handle, string name);
public void SetName (string name) { Node_SetName (handle, name);
Node.cppNode.h
binding.cpp
Node.cs
original API
generated
generated

10. Urho3D API
class Node : public Animatable
{
public:
Node(Context* context);
void SetName(const String& name);
};
DllExport void* Node_Node (Context * context) {
return new Node(context);
}
DllExport void Node_SetName (Node *target, const char * name) {
target->SetName (Urho3D::String(name));
}
public partial class Node : Animatable
{
private IntPtr handle;
[DllImport ("mono-urho")]
static extern IntPtr Node_Node (IntPtr context);
public Node (Context context) { handle = Node_Node (context.Handle); }
[DllImport ("mono-urho")]
static extern void Node_SetName (IntPtr handle, string name);
public void SetName (string name) { Node_SetName (handle, name);
Node.cppNode.h
binding.cpp
Node.cs
original API
generated
generated

11. Binding flow
Urho3D sources
(*.cpp, *.h)
Urho.pch
Generator (Binder)
binding.cpp *.cs
UrhoSharp.dll
Win: mono-urho.dll
Droid: libmono-urho.so
OSX: libmono-urho.dylib
iOS: urho.framework
nuget package
all-urho.cpp via clang
roslyn
• clang
• gcc
• msvc
clang.dll
Nrefactory.dll
PCL, Profile7

12. Object lifecycle
RefCounted:
• AddRef
• ReleaseRef
• RefsCount
• ~dctor
Node node = new Node(context)
1) Allocate a native object (Node* node = new Node)
scene.AddNode(node)
2) AddRef is called, callback to managed code
3) Managed code receives the callback, adds hard reference to node
scene.RemoveAll();
5) Managed code receives callback from native ~dctor,
removes reference. GC is now able to collect empty wrapper.
6) GC collects managed wrapper

13. Egor Bogatov
@EgorBo
github:
• UrhoSharp
• CppSharp