Integrating C++ system library

pusewicz · 2024-07-01T22:03:02.447Z

I'm having trouble trying to integrate Gosu in my Swift project. Adding SDL2 (with module.modulemap) was easy and works no problem. Bear in mind that I'm a complete noob to Swift.

I wanted to jump some hoops and add Gosu directly as it implements some of the functionality to create games easier compared to plain SDL2.

I have Gosu installed through Homebrew.

My Sources/CGosu/module.modulemap:

module CGosu [system] {
  umbrella header "/opt/homebrew/include/Gosu/Gosu.hpp"
  export *
}

My Package.swift:

// swift-tools-version: 5.10
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
  name: "SwiftGosu",
  platforms: [
    .macOS(.v14)
  ],
  targets: [
    .executableTarget(
      name: "SwiftGosu",
      dependencies: ["CGosu"],
      path: "Sources"
    ),
    .systemLibrary(
      name: "CGosu",
      providers: [.brew(["libgosu"])]
    ),
  ]
)

Output for swift run:

error: emit-module command failed with exit code 1 (use -v to see invocation)
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "/opt/homebrew/include/Gosu/Gosu.hpp"
        ^
/opt/homebrew/include/Gosu/Gosu.hpp:9:10: note: in file included from /opt/homebrew/include/Gosu/Gosu.hpp:9:
#include <Gosu/Audio.hpp>
         ^
/opt/homebrew/include/Gosu/Audio.hpp:3:10: note: in file included from /opt/homebrew/include/Gosu/Audio.hpp:3:
#include <Gosu/Fwd.hpp>
         ^
/opt/homebrew/include/Gosu/Fwd.hpp:3:1: error: unknown type name 'namespace'
namespace Gosu
^
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "/opt/homebrew/include/Gosu/Gosu.hpp"
        ^
/opt/homebrew/include/Gosu/Gosu.hpp:9:10: note: in file included from /opt/homebrew/include/Gosu/Gosu.hpp:9:
#include <Gosu/Audio.hpp>
         ^
/opt/homebrew/include/Gosu/Audio.hpp:3:10: note: in file included from /opt/homebrew/include/Gosu/Audio.hpp:3:
#include <Gosu/Fwd.hpp>
         ^
/opt/homebrew/include/Gosu/Fwd.hpp:3:15: error: expected ';' after top level declarator
namespace Gosu
              ^
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "/opt/homebrew/include/Gosu/Gosu.hpp"
        ^
/opt/homebrew/include/Gosu/Gosu.hpp:9:10: note: in file included from /opt/homebrew/include/Gosu/Gosu.hpp:9:
#include <Gosu/Audio.hpp>
         ^
/opt/homebrew/include/Gosu/Audio.hpp:4:10: note: in file included from /opt/homebrew/include/Gosu/Audio.hpp:4:
#include <Gosu/IO.hpp>
         ^
/opt/homebrew/include/Gosu/IO.hpp:4:10: error: 'algorithm' file not found
#include <algorithm>
         ^
/Users/piotr/Work/GitHub/SwiftGosu/Sources/main.swift:4:8: error: could not build Objective-C module 'CGosu'
import CGosu
       ^
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "/opt/homebrew/include/Gosu/Gosu.hpp"
        ^
/opt/homebrew/include/Gosu/Gosu.hpp:9:10: note: in file included from /opt/homebrew/include/Gosu/Gosu.hpp:9:
#include <Gosu/Audio.hpp>
         ^
/opt/homebrew/include/Gosu/Audio.hpp:3:10: note: in file included from /opt/homebrew/include/Gosu/Audio.hpp:3:
#include <Gosu/Fwd.hpp>
         ^
/opt/homebrew/include/Gosu/Fwd.hpp:3:1: error: unknown type name 'namespace'
namespace Gosu
^
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "/opt/homebrew/include/Gosu/Gosu.hpp"
        ^
/opt/homebrew/include/Gosu/Gosu.hpp:9:10: note: in file included from /opt/homebrew/include/Gosu/Gosu.hpp:9:
#include <Gosu/Audio.hpp>
         ^
/opt/homebrew/include/Gosu/Audio.hpp:3:10: note: in file included from /opt/homebrew/include/Gosu/Audio.hpp:3:
#include <Gosu/Fwd.hpp>
         ^
/opt/homebrew/include/Gosu/Fwd.hpp:3:15: error: expected ';' after top level declarator
namespace Gosu
              ^
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "/opt/homebrew/include/Gosu/Gosu.hpp"
        ^
/opt/homebrew/include/Gosu/Gosu.hpp:9:10: note: in file included from /opt/homebrew/include/Gosu/Gosu.hpp:9:
#include <Gosu/Audio.hpp>
         ^
/opt/homebrew/include/Gosu/Audio.hpp:4:10: note: in file included from /opt/homebrew/include/Gosu/Audio.hpp:4:
#include <Gosu/IO.hpp>
         ^
/opt/homebrew/include/Gosu/IO.hpp:4:10: error: 'algorithm' file not found
#include <algorithm>
         ^
/Users/piotr/Work/GitHub/SwiftGosu/Sources/main.swift:4:8: error: could not build Objective-C module 'CGosu'
import CGosu
       ^
error: fatalError

How should I go ahead and add it? Should I clone the Gosu repository directly to Sources/CGosu and use that instead? With the systemLibrary definition it seems I can't make it treat it as a C++ library.

xtremekforever · 2024-07-03T02:16:18.785Z

Hey, it looks like you need to enable CXX Interoperability mode in the project. See here: Swift.org - Setting Up Mixed-Language Swift and C++ Projects

By the looks of your Packge.swift, you’re importing Gosu as a C module which is why it’s whining about it. Have a look at the guide and see if you can enable CXX interop for the project.

jrose · 2024-07-03T05:55:40.032Z

…and per Modules — Clang 19.0.0git documentation, you can put requires cplusplus in your module definition to make sure this doesn't happen by accident.

pusewicz · 2024-07-03T09:46:47.998Z

Ok, this is now better. I also had to figure out that the main executable target had to link to the library, too so that it could find the symbols.

github.com

pusewicz/SwiftGosu/blob/main/Package.swift

// swift-tools-version: 5.10
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
  name: "SwiftGosu",
  platforms: [
    .macOS(.v14)
  ],
  targets: [
    .executableTarget(
      name: "SwiftGosu",
      dependencies: ["CGosuFFI"],
      path: "Sources",
      exclude: ["CGosuFFI"],
      swiftSettings: [.interoperabilityMode(.Cxx)],
      linkerSettings: [.linkedLibrary("gosu")]
    ),
    .systemLibrary(

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pusewicz · 2024-07-05T15:12:56.095Z

Thank you for the help @xtremekforever and @jrose!

xtremekforever · 2024-07-05T22:23:07.998Z

Glad you could get it working!!

pusewicz · 2024-07-06T15:24:02.776Z

@xtremekforever BTW. Do you know if it's possible to directly use namespaced C++ classes? Or do I need a C wrapper for those?

xtremekforever · 2024-07-06T17:09:05.282Z

I think it should be. In my case I was using namespaced classes from our proprietary library where all classes were under a “lib” namespace, and I did stuff like:

let myInstance = lib.MyClass()

I did have issues creating instances of classes that used fancy types like std::atomic and std::mutex- it seemed that having members using those type classes caused Swift to not even show the class, so they had to be wrapped in C functions to get instances instead.

Are you having issues seeing your namespaced classes?

pusewicz · 2024-07-08T08:02:54.407Z

Cool, I think I finally got it to work! Next step, inheritance (or wrapping?).

I've got this C++ class thing. In order to use it, I need to inherit from it, and override the update method.

github.com

gosu/gosu/blob/master/src/Window.cpp#L37-L59


      
          Gosu::Window::Window(int width, int height, unsigned window_flags, double update_interval)
              : m_impl(new Impl)
          {
              set_borderless(window_flags & WF_BORDERLESS);
              set_resizable(window_flags & WF_RESIZABLE);
          
              // Even in fullscreen mode, temporarily show the window in windowed mode to center it.
              // This ensures that the window will be centered correctly when exiting fullscreen mode.
              // Fixes https://github.com/gosu/gosu/issues/369
              // (This will implicitly create graphics() and input(), and make the OpenGL context current.)
              resize(width, height, false);
              SDL_SetWindowPosition(sdl_window(), SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED);
          
              // Really enable fullscreen if desired.
              resize(width, height, (window_flags & WF_FULLSCREEN));
          
              m_impl->update_interval = update_interval;
          
              input().on_button_down = [this](Button button) { button_down(button); };
              input().on_button_up = [this](Button button) { button_up(button); };

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Here's an example in C++.

github.com

gosu/gosu/blob/master/examples/Tutorial/Tutorial.cpp#L131-L196


      
          class GameWindow : public Gosu::Window
          {
              Gosu::Image background_image;
              Animation star_anim;
              Gosu::Font font;
          
              Player player;
              std::list<Star> stars;
          
          public:
              GameWindow()
              :   Window(640, 480), font(20)
              {
                  set_caption("Gosu Tutorial Game");
          
                  std::string filename = Gosu::resource_path("media/Space.png");
                  background_image = Gosu::Image(filename, Gosu::IF_TILEABLE);
          
                  filename = Gosu::resource_path("media/Star.png");
                  star_anim = Gosu::load_tiles(filename, 25, 25);

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@xtremekforever Would you know how could this be achieved in Swift? Directly trying to inherit does not work.

/Users/piotr/Work/GitHub/SwiftGosu/Sources/main.swift:6:24: error: 'Window' is not a member type of enum '__ObjC.Gosu'
class GameWindow: Gosu.Window {
                  ~~~~ ^
/opt/homebrew/include/Gosu/Window.hpp:23:11: note: record 'Window' is not automatically available: does not have a copy constructor or destructor; does this type have reference semantics?
    class Window : private Noncopyable
          ^
          SWIFT_SHARED_REFERENCE(<#retain#>, <#release#>)

Obviously, as you can tell, I'm new to C++/Swift, so I have no idea what I'm doing :P.

xtremekforever · 2024-07-09T14:02:09.370Z

When it comes to this I'm not sure if it's really possible in Swift right now. You may just need to make a class in C++ that inherits from it and provides an update method, and that maybe calls a Swift class method instead.