use a vtable instead of direct linking

ui/src/api.cxx

@@ -4,54 +4,13 @@
 #include <utility>
 
 namespace ffi {
-extern "C" Core* rt4_viewport_create(xcb_connection_t* connection, std::uint32_t window, std::uint32_t width, std::uint32_t height);
-extern "C" void rt4_viewport_destroy(Core* viewport);
-extern "C" void rt4_viewport_configure(Core* viewport, std::uint32_t width, std::uint32_t height);
-extern "C" void rt4_viewport_redraw(Core* viewport, const RedrawArgs* args);
+extern "C" ICore* rt4_viewport_create(xcb_connection_t* connection, std::uint32_t window, std::uint32_t width, std::uint32_t height);
 } // namespace ffi
 
-BoxCore::BoxCore(BoxCore&& b)
-	: ptr(std::exchange(b.ptr, {})) {
-}
-
-BoxCore::~BoxCore() {
-	reset();
-}
-
-BoxCore& BoxCore::operator=(BoxCore&& b) {
-	if (&b == this)
-		return *this;
-	std::swap(ptr, b.ptr);
-	b.reset();
-	return *this;
-}
-
 BoxCore BoxCore::from_xcb(xcb_connection_t* connection, std::uint32_t window, std::uint32_t width, std::uint32_t height) {
 	if (!connection)
 		throw std::logic_error("attempt to use a null connection");
 	if (!window)
 		throw std::logic_error("attempt to use a null window");
-	BoxCore out;
-	out.ptr.ptr = ffi::rt4_viewport_create(connection, window, width, height);
-	return out;
-}
-
-void BoxCore::reset() {
-	auto viewport = std::exchange(ptr, {});
-	if (viewport)
-		ffi::rt4_viewport_destroy(viewport.use());
-}
-
-ffi::Core* MutCore::use() const {
-	if (!ptr)
-		throw std::logic_error("attempt to use a null Core");
-	return ptr;
-}
-
-void MutCore::configure(std::uint32_t width, std::uint32_t height) const {
-	rt4_viewport_configure(use(), width, height);
-}
-
-void MutCore::redraw(const RedrawArgs& args) const {
-	rt4_viewport_redraw(use(), &args);
+	return BoxCore{ffi::rt4_viewport_create(connection, window, width, height)};
 }

ui/src/api.hxx

@@ -2,15 +2,32 @@
 
 #include <cstdint>
 
+#include <memory>
+
 struct xcb_connection_t;
 
+class IBoxed {
+	friend struct BoxDeleter;
+
+private:
+	~IBoxed() = delete;
+	virtual void destroy() = 0;
+};
+
+struct BoxDeleter {
+	void operator()(IBoxed* obj) {
+		obj->destroy();
+	}
+};
+
+template <typename T>
+using Box = std::unique_ptr<T, BoxDeleter>;
+
 struct alignas(16) Vec4 {
 	float x, y, z, w;
 };
 
 namespace ffi {
-struct Core;
-
 struct RedrawArgs {
 	float cam_yaw;
 	float cam_pitch;
@@ -21,36 +38,14 @@ struct RedrawArgs {
 
 using ffi::RedrawArgs;
 
-class MutCore {
-	friend class BoxCore;
-
+class ICore : public IBoxed {
 public:
-	explicit operator bool() const { return ptr; }
-
-	void configure(std::uint32_t width, std::uint32_t height) const;
-	void redraw(const RedrawArgs& args) const;
-
-private:
-	ffi::Core* ptr = nullptr;
-	ffi::Core* use() const;
+	virtual void configure(std::uint32_t width, std::uint32_t height) = 0;
+	virtual void redraw(const RedrawArgs& args) = 0;
 };
 
-class BoxCore {
+class BoxCore : public Box<ICore> {
 public:
-	BoxCore() = default;
-	BoxCore(const BoxCore&) = delete;
-	BoxCore(BoxCore&&);
-	BoxCore& operator=(const BoxCore&) = delete;
-	BoxCore& operator=(BoxCore&&);
-	~BoxCore();
-
-	explicit operator bool() const { return !!ptr; }
-	const MutCore* operator->() const { return &ptr; }
-
-	void reset();
-
+	using Box<ICore>::Box;
 	static BoxCore from_xcb(xcb_connection_t* connection, std::uint32_t window, std::uint32_t width, std::uint32_t height);
-
-private:
-	MutCore ptr;
 };

ui/src/lib.rs

@@ -4,11 +4,74 @@ use PROJECT_NAME::{Core, RedrawArgs, init_gpu_inner};
 use glam::{UVec2, uvec2};
 use raw_window_handle::{RawDisplayHandle, RawWindowHandle, XcbDisplayHandle, XcbWindowHandle};
 
+use crate::vtable::ICoreImpl;
+
+mod vtable {
+	use std::ops::{Deref, DerefMut};
+
+	use PROJECT_NAME::{Core, RedrawArgs};
+	use glam::uvec2;
+
+	#[repr(C)]
+	struct ICoreVTable {
+		destroy: unsafe extern "C" fn(this: Box<ICoreImpl>),
+		configure: unsafe extern "C" fn(this: &mut ICoreImpl, width: u32, height: u32),
+		redraw: unsafe extern "C" fn(this: &mut ICoreImpl, args: &RedrawArgs),
+	}
+
+	unsafe extern "C" fn destroy(this: Box<ICoreImpl>) {
+		drop(this);
+	}
+
+	unsafe extern "C" fn configure(this: &mut ICoreImpl, width: u32, height: u32) {
+		this.core.configure(uvec2(width, height));
+	}
+
+	unsafe extern "C" fn redraw(this: &mut ICoreImpl, args: &RedrawArgs) {
+		this.core.redraw(args);
+	}
+
+	static VTABLE: ICoreVTable = ICoreVTable {
+		destroy: destroy,
+		configure: configure,
+		redraw: redraw,
+	};
+
+	#[repr(C)]
+	pub(crate) struct ICoreImpl {
+		vtable: &'static ICoreVTable,
+		core: Core,
+	}
+
+	impl ICoreImpl {
+		pub(crate) fn new(core: Core) -> Box<Self> {
+			Box::new(ICoreImpl {
+				vtable: &VTABLE,
+				core,
+			})
+		}
+	}
+
+	impl DerefMut for ICoreImpl {
+		fn deref_mut(&mut self) -> &mut Self::Target {
+			&mut self.core
+		}
+	}
+
+	impl Deref for ICoreImpl {
+		type Target = Core;
+
+		fn deref(&self) -> &Self::Target {
+			&self.core
+		}
+	}
+}
+
 unsafe fn create_viewport(
 	display: impl Into<RawDisplayHandle>,
 	window: impl Into<RawWindowHandle>,
 	size: UVec2,
-) -> Box<Core> {
+) -> Box<ICoreImpl> {
 	let target = wgpu::SurfaceTargetUnsafe::RawHandle {
 		raw_display_handle: display.into(),
 		raw_window_handle: window.into(),
@@ -17,7 +80,7 @@ unsafe fn create_viewport(
 		instance.create_surface_unsafe(target)
 	}))
 	.unwrap();
-	Box::new(Core::new(gpu, size))
+	ICoreImpl::new(Core::new(gpu, size))
 }
 
 #[unsafe(no_mangle)]
@@ -26,23 +89,8 @@ unsafe extern "C" fn rt4_viewport_create(
 	window: NonZero<u32>,
 	width: u32,
 	height: u32,
-) -> Box<Core> {
+) -> Box<ICoreImpl> {
 	let display = XcbDisplayHandle::new(Some(connection), 0);
 	let window = XcbWindowHandle::new(window);
 	unsafe { create_viewport(display, window, uvec2(width, height)) }
 }
-
-#[unsafe(no_mangle)]
-unsafe extern "C" fn rt4_viewport_destroy(viewport: Box<Core>) {
-	drop(viewport);
-}
-
-#[unsafe(no_mangle)]
-unsafe extern "C" fn rt4_viewport_configure(viewport: &mut Core, width: u32, height: u32) {
-	viewport.configure(uvec2(width, height));
-}
-
-#[unsafe(no_mangle)]
-unsafe extern "C" fn rt4_viewport_redraw(viewport: &mut Core, args: &RedrawArgs) {
-	viewport.redraw(args);
-}