godot/modules/mono/glue/GodotSharp/GodotSharp/Core/NodePath.cs
Ignacio Roldán Etcheverry 483071716e C#: Move marshaling logic and generated glue to C#
We will be progressively moving most code to C#.
The plan is to only use Mono's embedding APIs to set things at launch.
This will make it much easier to later support CoreCLR too which
doesn't have rich embedding APIs.

Additionally the code in C# is more maintainable and makes it easier
to implement new features, e.g.: runtime codegen which we could use to
avoid using reflection for marshaling everytime a field, property or
method is accessed.

SOME NOTES ON INTEROP

We make the same assumptions as GDNative about the size of the Godot
structures we use. We take it a bit further by also assuming the layout
of fields in some cases, which is riskier but let's us squeeze out some
performance by avoiding unnecessary managed to native calls.

Code that deals with native structs is less safe than before as there's
no RAII and copy constructors in C#. It's like using the GDNative C API
directly. One has to take special care to free values they own.
Perhaps we could use roslyn analyzers to check this, but I don't know
any that uses attributes to determine what's owned or borrowed.

As to why we maily use pointers for native structs instead of ref/out:
- AFAIK (and confirmed with a benchmark) ref/out are pinned
  during P/Invoke calls and that has a cost.
- Native struct fields can't be ref/out in the first place.
- A `using` local can't be passed as ref/out, only `in`. Calling a
  method or property on an `in` value makes a silent copy, so we want
  to avoid `in`.

REGARDING THE BUILD SYSTEM

There's no longer a `mono_glue=yes/no` SCons options. We no longer
need to build with `mono_glue=no`, generate the glue and then build
again with `mono_glue=yes`. We build only once and generate the glue
(which is in C# now).
However, SCons no longer builds the C# projects for us. Instead one
must run `build_assemblies.py`, e.g.:
```sh
%godot_src_root%/modules/mono/build_scripts/build_assemblies.py \
        --godot-output-dir=%godot_src_root%/bin \
        --godot-target=release_debug`
```
We could turn this into a custom build target, but I don't know how
to do that with SCons (it's possible with Meson).

OTHER NOTES

Most of the moved code doesn't follow the C# naming convention and
still has the word Mono in the names despite no longer dealing with
Mono's embedding APIs. This is just temporary while transitioning,
to make it easier to understand what was moved where.
2021-08-20 10:24:56 +02:00

124 lines
3.8 KiB
C#

using System;
using System.Runtime.CompilerServices;
using Godot.NativeInterop;
namespace Godot
{
public sealed class NodePath : IDisposable
{
internal godot_node_path NativeValue;
~NodePath()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
public void Dispose(bool disposing)
{
// Always dispose `NativeValue` even if disposing is true
NativeValue.Dispose();
}
private NodePath(godot_node_path nativeValueToOwn)
{
NativeValue = nativeValueToOwn;
}
// Explicit name to make it very clear
internal static NodePath CreateTakingOwnershipOfDisposableValue(godot_node_path nativeValueToOwn)
=> new NodePath(nativeValueToOwn);
public NodePath()
{
}
public NodePath(string path)
{
if (!string.IsNullOrEmpty(path))
NativeValue = NativeFuncs.godotsharp_node_path_new_from_string(path);
}
public static implicit operator NodePath(string from) => new NodePath(from);
public static implicit operator string(NodePath from) => from.ToString();
public override unsafe string ToString()
{
if (IsEmpty)
return string.Empty;
godot_string dest;
godot_node_path src = NativeValue;
NativeFuncs.godotsharp_node_path_as_string(&dest, &src);
using (dest)
return Marshaling.mono_string_from_godot(&dest);
}
public NodePath GetAsPropertyPath()
{
godot_node_path propertyPath = default;
godot_icall_NodePath_get_as_property_path(ref NativeValue, ref propertyPath);
return CreateTakingOwnershipOfDisposableValue(propertyPath);
}
public string GetConcatenatedSubNames()
{
return godot_icall_NodePath_get_concatenated_subnames(ref NativeValue);
}
public string GetName(int idx)
{
return godot_icall_NodePath_get_name(ref NativeValue, idx);
}
public int GetNameCount()
{
return godot_icall_NodePath_get_name_count(ref NativeValue);
}
public string GetSubName(int idx)
{
return godot_icall_NodePath_get_subname(ref NativeValue, idx);
}
public int GetSubNameCount()
{
return godot_icall_NodePath_get_subname_count(ref NativeValue);
}
public bool IsAbsolute()
{
return godot_icall_NodePath_is_absolute(ref NativeValue);
}
public bool IsEmpty => godot_node_path.IsEmpty(in NativeValue);
[MethodImpl(MethodImplOptions.InternalCall)]
private static extern void godot_icall_NodePath_get_as_property_path(ref godot_node_path ptr, ref godot_node_path dest);
[MethodImpl(MethodImplOptions.InternalCall)]
private static extern string godot_icall_NodePath_get_concatenated_subnames(ref godot_node_path ptr);
[MethodImpl(MethodImplOptions.InternalCall)]
private static extern string godot_icall_NodePath_get_name(ref godot_node_path ptr, int arg1);
[MethodImpl(MethodImplOptions.InternalCall)]
private static extern int godot_icall_NodePath_get_name_count(ref godot_node_path ptr);
[MethodImpl(MethodImplOptions.InternalCall)]
private static extern string godot_icall_NodePath_get_subname(ref godot_node_path ptr, int arg1);
[MethodImpl(MethodImplOptions.InternalCall)]
private static extern int godot_icall_NodePath_get_subname_count(ref godot_node_path ptr);
[MethodImpl(MethodImplOptions.InternalCall)]
private static extern bool godot_icall_NodePath_is_absolute(ref godot_node_path ptr);
}
}