metal: Migrate to objc2 architecture with objc2-metal bindings

The current `objc` crate stack is completely unmaintained and has
severely fallen out of date with no updates for over 4 years.  The
`metal-rs` crate, built on top of this architecture, is completely
written by hand which is tedious to keep up-to-date, not to mention
has inconsistencies in its implementation.

All of this is superseded by the new `objc2` crate stack built by
@madsmtm.  Beyond providing what seems like a better, safer abstraction
over Objective-C, _all_ bindings are completely autogenerated meaning
we'll no longer lag behind upstream bindings (requiring painstaking
manual patching) or have inconsistencies in the implementations, as long
as the generator is properly able to represent the bindings.

Cargo.toml

@@ -34,7 +34,18 @@ egui = { version = ">=0.24, <=0.27", optional = true, default-features = false }
 egui_extras = { version = ">=0.24, <=0.27", optional = true, default-features = false }
 
 [target.'cfg(any(target_os = "macos", target_os = "ios"))'.dependencies]
-metal = { version = "0.27.0", default-features = false, features = ["link", "dispatch"], optional = true }
+objc2 = { version = "0.5", default-features = false, optional = true }
+objc2-foundation = { version = "0.2", default-features = false, optional = true }
+objc2-metal = { version = "0.2.0", default-features = false, features = [
+    "MTLAccelerationStructure",
+    "MTLBuffer",
+    "MTLDevice",
+    "MTLHeap",
+    # "MTLPixelFormat",
+    "MTLResource",
+    "MTLTexture",
+    "std",
+], optional = true }
 
 [target.'cfg(windows)'.dependencies]
 # Only needed for public-winapi interop helpers
@@ -71,6 +82,11 @@ features = [
     "Win32_Graphics_Dxgi_Common",
 ]
 
+[target.'cfg(any(target_os = "macos", target_os = "ios"))'.dev-dependencies]
+objc2-metal = { version = "0.2.0", default-features = false, features = [
+    "MTLPixelFormat",
+] }
+
 [[example]]
 name = "vulkan-buffer"
 required-features = ["vulkan", "ash/loaded"]
@@ -91,11 +107,8 @@ required-features = ["metal"]
 visualizer = ["dep:egui", "dep:egui_extras"]
 vulkan = ["dep:ash"]
 d3d12 = ["dep:windows"]
-metal = ["dep:metal"]
+metal = ["dep:objc2", "dep:objc2-metal", "dep:objc2-foundation"]
 # Expose helper functionality for winapi types to interface with gpu-allocator, which is primarily windows-rs driven
 public-winapi = ["dep:winapi"]
 
-default = ["d3d12", "vulkan"]
-
-[patch.crates-io]
-metal = { git = "https://github.com/Traverse-Research/metal-rs", rev = "a354c33" }
+default = ["d3d12", "vulkan", "metal"]

examples/metal-buffer.rs

@@ -2,11 +2,17 @@ use std::sync::Arc;
 
 use gpu_allocator::metal::{AllocationCreateDesc, Allocator, AllocatorCreateDesc};
 use log::info;
+use metal::MTLDevice as _;
+use objc2::rc::Id;
+use objc2_foundation::NSArray;
+use objc2_metal as metal;
 
 fn main() {
     env_logger::Builder::from_env(env_logger::Env::default().default_filter_or("trace")).init();
 
-    let device = Arc::new(metal::Device::system_default().unwrap());
+    let device = unsafe { metal::MTLCreateSystemDefaultDevice() };
+    // TODO: Not SendSync
+    let device = Arc::new(unsafe { Id::from_raw(device) }.expect("No MTLDevice found"));
 
     // Setting up the allocator
     let mut allocator = Allocator::new(&AllocatorCreateDesc {
@@ -60,11 +66,11 @@ fn main() {
 
     // Test allocating texture
     {
-        let texture_desc = metal::TextureDescriptor::new();
-        texture_desc.set_pixel_format(metal::MTLPixelFormat::RGBA8Unorm);
-        texture_desc.set_width(64);
-        texture_desc.set_height(64);
-        texture_desc.set_storage_mode(metal::MTLStorageMode::Private);
+        let texture_desc = unsafe { metal::MTLTextureDescriptor::new() };
+        texture_desc.setPixelFormat(metal::MTLPixelFormat::RGBA8Unorm);
+        unsafe { texture_desc.setWidth(64) };
+        unsafe { texture_desc.setHeight(64) };
+        texture_desc.setStorageMode(metal::MTLStorageMode::Private);
         let allocation_desc =
             AllocationCreateDesc::texture(&device, "Test allocation (Texture)", &texture_desc);
         let allocation = allocator.allocate(&allocation_desc).unwrap();
@@ -75,14 +81,14 @@ fn main() {
 
     // Test allocating acceleration structure
     {
-        let empty_array = metal::Array::from_slice(&[]);
-        let acc_desc = metal::PrimitiveAccelerationStructureDescriptor::descriptor();
-        acc_desc.set_geometry_descriptors(empty_array);
-        let sizes = device.acceleration_structure_sizes_with_descriptor(&acc_desc);
+        let empty_array = NSArray::from_slice(&[]);
+        let acc_desc = metal::MTLPrimitiveAccelerationStructureDescriptor::descriptor();
+        acc_desc.setGeometryDescriptors(Some(&empty_array));
+        let sizes = device.accelerationStructureSizesWithDescriptor(&acc_desc);
         let allocation_desc = AllocationCreateDesc::acceleration_structure_with_size(
             &device,
             "Test allocation (Acceleration structure)",
-            sizes.acceleration_structure_size,
+            sizes.accelerationStructureSize as u64,
             gpu_allocator::MemoryLocation::GpuOnly,
         );
         let allocation = allocator.allocate(&allocation_desc).unwrap();

src/d3d12/mod.rs

@@ -1,5 +1,3 @@
-#![deny(clippy::unimplemented, clippy::unwrap_used, clippy::ok_expect)]
-
 use std::{backtrace::Backtrace, fmt, sync::Arc};
 
 use log::{debug, warn, Level};

src/lib.rs

@@ -206,6 +206,7 @@
 //! # #[cfg(not(feature = "metal"))]
 //! # fn main() {}
 //! ```
+#![deny(clippy::unimplemented, clippy::unwrap_used, clippy::ok_expect)]
 
 mod result;
 pub use result::*;