vkgen 0.1.8

# vkgen
Generates Rust source code from vk.xml

### This crate offers
- an easy to use cli tool
- no external dependencies except libloading
- only ~1.000 lines of code which ensures simple maintainability
- a generator that can easily be modified to support other languages (just replace vkgen::gen() with your own code)
- support for all future versions of the Vulkan API (as long as the structure of the registry does not change)

### General information
- libloading is required to load vkGetInstanceProcAddr from the Vulkan shared library
- all functions are loaded dynamically during runtime via vkGetInstanceProcAddr and vkGetDeviceProcAddr
- a very thin wrapper is generated for all dispatchable handles to store function pointers / parent handles,
  but without any remarkable performance penalties

## Usage
### Step 1
Download vk.xml from the official Vulkan-Headers repository (https://github.com/KhronosGroup/Vulkan-Headers/blob/master/registry/vk.xml)

### Step 2
Generate Rust source code from vk.xml

```$ vkgen <input file> <output file>```

- `input file` should be the Vulkan registry (vk.xml)
- `output file` will be created if it does not exist

### Step 3
Add libloading to cargo.toml
```
[dependencies]
libloading = "0.5.0"
```
This is required to load vkGetInstanceProcAddr from the Vulkan shared library.

### Step 4
Load libvulkan in order to use the generated functions
```rust
unsafe { vkLoad("path/to/libvulkan"); }
```
Note: vkLoad() only loads vkGetInstanceProcAddr from the shared library, all other
      functions are loaded dynamically via vkGetInstanceProcAddr and
      vkGetDeviceProcAddr to avoid additional dispatch overhead.

## Examples
This simple example demonstrates how to load libvulkan on linux and output the instance
version (1.1.0). vk.rs is the file containing the generated Rust source code.
The location of libvulkan.so/vulkan.dll may vary depending on the OS.
```rust
mod vk;

use self::vk::*;

fn main() {
	unsafe { vkLoad("/usr/lib/x86_64-linux-gnu/libvulkan.so.1.1.92"); }

	let mut v: u32 = 0;
	vkEnumerateInstanceVersion(&mut v as *mut u32);
	println!("vulkan instance version is {}.{}.{}", VK_VERSION_MAJOR(v), VK_VERSION_MINOR(v), VK_VERSION_PATCH(v));
}

```

## Known Issues
- enum aliases are not generated (this is because Rust does not allow two enum constants with the same value)