lib: Provide entrypoint through Ash loader w.o. implementing Entry (#56)

* lib: Provide entrypoint through Ash loader w.o. implementing Entry

Ash recently [dropped all traits](1) to simplify `ash::Device` usage,
but this also disallows ash-molten from overriding the `EntryV1_0` trait
to provide a static entrypoint intead.

Fortunately ash-molten can simply pass a library loading closure that
returns the static address of `vkGetInstanceProcAddr` to
`EntryCustom::new_custom`, getting rid of the copied `fn
create_instance` implementation at the same time.

[1]: https://github.com/MaikKlein/ash/pull/412

* cargo: Disable unneeded `libloading` feature in Ash

The entry-point is statically linked from `MoltenVK` and does not need
any dlopen nor dlsym functionality.

* Fix some typos

Cargo.toml

@@ -14,7 +14,7 @@ documentation = "https://docs.rs/ash-molten"
 build = "build/build.rs"
 
 [dependencies]
-ash = "0.32"
+ash = { version = "0.33", default-features = false }
 
 [build-dependencies]
 anyhow = "1.0"

README.md

@@ -13,15 +13,15 @@ Requires Xcode 12 and Mac OS 10.15 (Catalina) to compile.
 
 ## Why?
 
-* You want to compile down to a single binary that doesn't need any enviroment variables to bet set.
+* You want to compile down to a single binary that doesn't need any environment variables to bet set.
 
 * You just want to try out [MoltenVK](https://github.com/KhronosGroup/MoltenVK) without needing to setup the SDK.
 
 ## Why not?
 
-* [ash](https://github.com/MaikKlein/ash) already supports [MoltenVK](https://github.com/KhronosGroup/MoltenVK) via runtime linking. Runtime linking is the prefered way of using Vulkan because the loader can be updated at anytime without needing to recompile.
+* [ash](https://github.com/MaikKlein/ash) already supports [MoltenVK](https://github.com/KhronosGroup/MoltenVK) via runtime linking. Runtime linking is the preferred way of using Vulkan because the loader can be updated at anytime without needing to recompile.
 
-* `ash-molten` doesn't have access to the validation layers and thefore can not output any debug information.
+* `ash-molten` doesn't have access to the validation layers and therefore can not output any debug information.
 
 ## How?
 
@@ -62,7 +62,7 @@ To update the version of [MoltenVK](https://github.com/KhronosGroup/MoltenVK) us
 - In `build.rs`, change `static VERSION = "1.1.0"` to the new [MoltenVK release](https://github.com/KhronosGroup/MoltenVK/releases) tag name
 - Update the crate version in `Cargo.toml`
   - Bump the patch version
-  - Set the version metadata to the MoltenVK release. 
+  - Set the version metadata to the MoltenVK release.
   - E.g. `0.2.0+37` -> `0.2.1+38`.
 
 ### Updating pre-built version

build/build.rs

@@ -91,7 +91,7 @@ mod mac {
     }
 
     // Features are not used inside build scripts, so we have to explicitly query them from the
-    // enviroment
+    // environment
     pub(crate) fn is_feature_enabled(feature: &str) -> bool {
         std::env::vars()
             .filter_map(|(flag, _)| {
@@ -136,7 +136,7 @@ mod mac {
         });
 
         if Path::new(&checkout_dir).exists() {
-            // Don't pull if a specific hash has been checkedout
+            // Don't pull if a specific hash has been checked out
             if MOLTEN_VK_PATCH.is_none() {
                 let git_status = Command::new("git")
                     .current_dir(&checkout_dir)
@@ -186,7 +186,7 @@ mod mac {
                 "ios" => ("ios", "iOS"),
                 target => panic!("unknown target '{}'", target),
             },
-            Err(e) => panic!("failed to determinte target os '{}'", e),
+            Err(e) => panic!("failed to determine target os '{}'", e),
         };
 
         let status = Command::new("sh")
@@ -274,7 +274,7 @@ use std::{
 #[cfg(any(target_os = "macos", target_os = "ios"))]
 fn main() {
     use crate::mac::*;
-    // The 'external' feature was not enabled. Molten will be built automaticaly.
+    // The 'external' feature was not enabled. Molten will be built automatically.
     let external_enabled = is_feature_enabled("EXTERNAL");
     let pre_built_enabled = is_feature_enabled("PRE_BUILT");
 
@@ -283,7 +283,7 @@ fn main() {
 
     assert!(
         !(external_enabled && pre_built_enabled),
-        "external and prebuild cannot be active at the same time"
+        "external and prebuilt cannot be active at the same time"
     );
 
     if !external_enabled {

src/bin/main.rs

@@ -70,14 +70,11 @@
 // crate-specific exceptions:
 #![allow(unsafe_code)]
 
-use ash::{
-    version::{EntryV1_0, InstanceV1_0},
-    vk,
-};
+use ash::vk;
 use std::ffi::CString;
 fn main() {
     unsafe {
-        let entry = ash_molten::MoltenEntry::load().expect("Unable to load Molten");
+        let entry = ash_molten::MoltenEntry::load();
         let app_name = CString::new("Hello Static Molten").unwrap();
 
         let appinfo = vk::ApplicationInfo::builder()
@@ -85,7 +82,7 @@ fn main() {
             .application_version(0)
             .engine_name(&app_name)
             .engine_version(0)
-            .api_version(vk::make_version(1, 0, 0));
+            .api_version(vk::make_api_version(0, 1, 0, 0));
 
         let create_info = vk::InstanceCreateInfo::builder().application_info(&appinfo);
         let instance = entry.create_instance(&create_info, None).expect("Instance");

src/lib.rs

@@ -70,7 +70,9 @@
 // crate-specific exceptions:
 #![allow(unsafe_code)]
 
-use ash::{version::EntryV1_0, vk, Instance, InstanceError, RawPtr};
+use std::ops::Deref;
+
+use ash::{vk, EntryCustom};
 
 extern "system" {
     fn vkGetInstanceProcAddr(
@@ -79,62 +81,28 @@ extern "system" {
     ) -> vk::PFN_vkVoidFunction;
 }
 
-extern "system" fn get_instance_proc_addr(
-    instance: vk::Instance,
-    p_name: *const std::os::raw::c_char,
-) -> vk::PFN_vkVoidFunction {
-    unsafe { vkGetInstanceProcAddr(instance, p_name) }
-}
-
 /// The entry point for the statically linked molten library
-pub struct MoltenEntry {
-    static_fn: vk::StaticFn,
-    entry_fn_1_0: vk::EntryFnV1_0,
-}
+pub struct MoltenEntry(EntryCustom<()>);
 
 impl MoltenEntry {
-    /// Fetches the function pointer to `get_instance_proc_addr` which is statically linked. This
-    /// function can not fail.
-    pub fn load() -> Result<MoltenEntry, ash::LoadingError> {
-        let static_fn = vk::StaticFn {
-            get_instance_proc_addr,
-        };
-
-        let entry_fn_1_0 = vk::EntryFnV1_0::load(|name| unsafe {
-            std::mem::transmute(
-                static_fn.get_instance_proc_addr(vk::Instance::null(), name.as_ptr()),
-            )
-        });
-
-        Ok(MoltenEntry {
-            static_fn,
-            entry_fn_1_0,
-        })
+    /// Fetches the function pointer to `vkGetInstanceProcAddr` which is statically linked.
+    pub fn load() -> Self {
+        Self(
+            EntryCustom::new_custom((), |(), name| {
+                assert_eq!(name.to_bytes_with_nul(), b"vkGetInstanceProcAddr\0");
+                vkGetInstanceProcAddr as _
+            })
+            // This can never fail because we always return the address of
+            // `vkGetInstanceProcAddr` from the closure:
+            .unwrap(),
+        )
     }
 }
-impl EntryV1_0 for MoltenEntry {
-    type Instance = Instance;
-    #[doc = "<https://www.khronos.org/registry/vulkan/specs/1.1-extensions/man/html/vkCreateInstance.html>"]
-    unsafe fn create_instance(
-        &self,
-        create_info: &vk::InstanceCreateInfo,
-        allocation_callbacks: Option<&vk::AllocationCallbacks>,
-    ) -> Result<Self::Instance, InstanceError> {
-        let mut instance: vk::Instance = vk::Instance::null();
-        let err_code = self.fp_v1_0().create_instance(
-            create_info,
-            allocation_callbacks.as_raw_ptr(),
-            &mut instance,
-        );
-        if err_code != vk::Result::SUCCESS {
-            return Err(InstanceError::VkError(err_code));
-        }
-        Ok(Instance::load(&self.static_fn, instance))
-    }
-    fn fp_v1_0(&self) -> &vk::EntryFnV1_0 {
-        &self.entry_fn_1_0
-    }
-    fn static_fn(&self) -> &vk::StaticFn {
-        &self.static_fn
+
+impl Deref for MoltenEntry {
+    type Target = EntryCustom<()>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
     }
 }