godot/modules/mono/mono_gd/gd_mono_marshal.h
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

107 lines
4.5 KiB
C++

/*************************************************************************/
/* gd_mono_marshal.h */
/*************************************************************************/
/* This file is part of: */
/* GODOT ENGINE */
/* https://godotengine.org */
/*************************************************************************/
/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur. */
/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md). */
/* */
/* Permission is hereby granted, free of charge, to any person obtaining */
/* a copy of this software and associated documentation files (the */
/* "Software"), to deal in the Software without restriction, including */
/* without limitation the rights to use, copy, modify, merge, publish, */
/* distribute, sublicense, and/or sell copies of the Software, and to */
/* permit persons to whom the Software is furnished to do so, subject to */
/* the following conditions: */
/* */
/* The above copyright notice and this permission notice shall be */
/* included in all copies or substantial portions of the Software. */
/* */
/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, */
/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF */
/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY */
/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, */
/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE */
/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
/*************************************************************************/
#ifndef GDMONOMARSHAL_H
#define GDMONOMARSHAL_H
#include "core/variant/variant.h"
#include "gd_mono.h"
#include "gd_mono_utils.h"
namespace GDMonoMarshal {
template <typename T>
T unbox(MonoObject *p_obj) {
return *(T *)mono_object_unbox(p_obj);
}
Variant::Type managed_to_variant_type(const ManagedType &p_type, bool *r_nil_is_variant = nullptr);
bool try_get_array_element_type(const ManagedType &p_array_type, ManagedType &r_elem_type);
// String
_FORCE_INLINE_ String mono_string_to_godot_not_null(MonoString *p_mono_string) {
char32_t *utf32 = (char32_t *)mono_string_to_utf32(p_mono_string);
String ret = String(utf32);
mono_free(utf32);
return ret;
}
_FORCE_INLINE_ String mono_string_to_godot(MonoString *p_mono_string) {
if (p_mono_string == nullptr) {
return String();
}
return mono_string_to_godot_not_null(p_mono_string);
}
_FORCE_INLINE_ MonoString *mono_string_from_godot(const String &p_string) {
return mono_string_from_utf32((mono_unichar4 *)(p_string.get_data()));
}
// Variant
MonoObject *variant_to_mono_object_of_type(const Variant &p_var, const ManagedType &p_type);
MonoObject *variant_to_mono_object(const Variant &p_var);
// These overloads were added to avoid passing a `const Variant *` to the `const Variant &`
// parameter. That would result in the `Variant(bool)` copy constructor being called as
// pointers are implicitly converted to bool. Implicit conversions are f-ing evil.
_FORCE_INLINE_ MonoObject *variant_to_mono_object_of_type(const Variant *p_var, const ManagedType &p_type) {
return variant_to_mono_object_of_type(*p_var, p_type);
}
_FORCE_INLINE_ MonoObject *variant_to_mono_object(const Variant *p_var) {
return variant_to_mono_object(*p_var);
}
Variant mono_object_to_variant(MonoObject *p_obj);
Variant mono_object_to_variant_no_err(MonoObject *p_obj);
/// Tries to convert the MonoObject* to Variant and then convert the Variant to String.
/// If the MonoObject* cannot be converted to Variant, then 'ToString()' is called instead.
String mono_object_to_variant_string(MonoObject *p_obj, MonoException **r_exc);
// Array
MonoArray *Array_to_mono_array(const Array &p_array);
Array mono_array_to_Array(MonoArray *p_array);
// PackedStringArray
MonoArray *PackedStringArray_to_mono_array(const PackedStringArray &p_array);
} // namespace GDMonoMarshal
#endif // GDMONOMARSHAL_H