We're targeting .NET 5 for now to make development easier while
.NET 6 is not yet released.
TEMPORARY REGRESSIONS
---------------------
Assembly unloading is not implemented yet. As such, many Godot
resources are leaked at exit. This will be re-implemented later
together with assembly hot-reloading.
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.
Godot.NET.Sdk
-------------
Godot uses its own custom MSBuild Sdk for game
projects. This new Sdk adds its own functionality
on top of 'Microsoft.NET.Sdk'.
The new Sdk is resolved from the NuGet package.
All the default boilerplate was moved from game
projects to the Sdk. The default csproj for
game project can now be as simple as:
```
<Project Sdk="Godot.NET.Sdk/4.0.0-dev2">
<PropertyGroup>
<TargetFramework>netstandard2.1</TargetFramework>
</PropertyGroup>
</Project>
```
Source files are included by automatically so
Godot no longer needs to keep the csproj in sync
when creating new source files.
Define constants
----------------
Godot defines a list of constants for conditional
compilation. When exporting games, this list also
included engine 'features' and platform 'bits'.
There were a few problems with that:
- The 'features' constants were only defined when
exporting games. Not when building the game for
running in the editor player.
- If the project was built externally by an IDE,
the constants wouldn't be defined at all.
The new Sdk assigns default values to these
constants when not built from the Godot editor,
i.e.: when built from an IDE or from the command
line. The default define constants are determined
from the system MSBuild is running on.
However, it's not possible for MSBuild to
determine the set of supported engine features.
It's also not possible to determine if a project
is being built to run on a 32-bit or 64-bit
Godot executable.
As such the 'features' and 'bits' constants had
to be removed.
The benefit of checking those at compile time
was questionable, and they can still be checked
at runtime.
The new list of define constants includes:
- GODOT
- GODOT_<PLATFORM>
Defaults to the platform MSBuild is running on.
- GODOT_<PC/MOBILE/WEB>
- TOOLS
When building with the 'Debug' configuration
(editor and editor player).
- GODOT_REAL_T_IS_DOUBLE
Not defined by default unless $(GodotRealTIsDouble)
is overriden to be 'true'.
.NET Standard
-------------
The target framework of game projects was changed
to 'netstandard2.1'.
By adding a reference to the 'Microsoft.NETFramework.ReferenceAssemblies' nuget
package, we can build projects targeting .NET Framework with the dotnet CLI.
By referencing this package we also don't need to install Mono on Linux/macOS
or .NET Framework on Windows, as the assemblies are taken from the package.
Previously we had a placeholder solution called 'Managed' to benefit from
tooling while editing the a part of the C# API.
Later the bindings generator would create the final 'GodotSharp' solution
including these C# files as well as the auto-generated C# API.
Now we replaced the 'Managed' solution with the final 'GodotSharp' solution
which is no longer auto-generated, and the bindings generator only takes
care of the auto-generated C# API.
This has the following benefits:
- It's less confusing as there will no longer be two versions of the same file
(the original and a generated copy of it). Now there's only one.
- We no longer need placeholder for auto-generated API classes, like Node or
Resource. We used them for benefiting from tooling. Now we can just use the
auto-generated API itself.
- Simplifies the build system and bindings generator. Removed lot of code
that is not needed anymore.
Also added a post-build target to the GodotTools project to copy the output to
the data dir. This makes it easy to iterate when doing changes to GodotTools,
as SCons doesn't have to be executed anymore just to copy these new files.
Ignacio Roldán Etcheverry