ash/README.md

Ash
=

A very lightweight wrapper around Vulkan
-

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## Overview
- [x] A true Vulkan API without compromises
- [x] Convenience features without limiting functionality
- [x] Additional type safety
- [x] Device local function pointer loading
- [x] No validation, everything is **unsafe**
- [x] Generated from `vk.xml`
- [x] Support for Vulkan `1.1`, `1.2`

## Features
### Explicit returns with `Result`
```rust
// function signature
pub fn create_instance(&self,
                       create_info: &vk::InstanceCreateInfo,
                       allocation_callbacks: Option<&vk::AllocationCallbacks>)
                       -> Result<Instance, InstanceError> { .. }
let instance = entry.create_instance(&create_info, None)
    .expect("Instance creation error");
```


### `Vec<T>` instead of mutable slices

```rust
pub fn get_swapchain_images(&self,
                            swapchain: vk::SwapchainKHR)
                            -> VkResult<Vec<vk::Image>>;
let present_images = swapchain_loader.get_swapchain_images_khr(swapchain).unwrap();
```
*Note*: Functions don't return `Vec<T>` if this would limit the functionality. See `p_next`.

### Slices
```rust
pub fn cmd_pipeline_barrier(&self,
                            command_buffer: vk::CommandBuffer,
                            src_stage_mask: vk::PipelineStageFlags,
                            dst_stage_mask: vk::PipelineStageFlags,
                            dependency_flags: vk::DependencyFlags,
                            memory_barriers: &[vk::MemoryBarrier],
                            buffer_memory_barriers: &[vk::BufferMemoryBarrier],
                            image_memory_barriers: &[vk::ImageMemoryBarrier]);
```

### Strongly typed handles

Each Vulkan handle type is exposed as a newtyped struct for improved type safety. Null handles can be constructed with
`T::null()`, and handles may be freely converted to and from `u64` with `Handle::from_raw` and `Handle::as_raw` for
interop with non-Ash Vulkan code.

### Default implementation for all types
```rust
// No need to manually set the structure type
let desc_alloc_info = vk::DescriptorSetAllocateInfo {
    descriptor_pool: self.pool,
    descriptor_set_count: self.layouts.len() as u32,
    p_set_layouts: self.layouts.as_ptr(),
    ..Default::default()
};
```
### Builder pattern

```rust
// We lose all lifetime information when we call `.build()`. Be careful!
let queue_info = [vk::DeviceQueueCreateInfo::builder()
    .queue_family_index(queue_family_index)
    .queue_priorities(&priorities)
    .build()];

// We don't need to call `.build()` here because builders implement `Deref`.
let device_create_info = vk::DeviceCreateInfo::builder()
    .queue_create_infos(&queue_info)
    .enabled_extension_names(&device_extension_names_raw)
    .enabled_features(&features);

let device: Device = instance
    .create_device(pdevice, &device_create_info, None)
    .unwrap();
```

To not lose this lifetime single items can be "cast" to a slice of length _one_ with `std::slice::from_ref` while still taking advantage of `Deref`:

```rust
let queue_info = vk::DeviceQueueCreateInfo::builder()
    .queue_family_index(queue_family_index)
    .queue_priorities(&priorities);

let device_create_info = vk::DeviceCreateInfo::builder()
    .queue_create_infos(std::slice::from_ref(&queue_info))
    ...;
```

Builders have an explicit lifetime, and are marked as `#[repr(transparent)]`.
```rust
#[repr(transparent)]
pub struct DeviceCreateInfoBuilder<'a> {
    inner: DeviceCreateInfo,
    marker: ::std::marker::PhantomData<&'a ()>,
}
impl<'a> DeviceCreateInfoBuilder<'a> {
    //...
    pub fn queue_create_infos(
        mut self,
        queue_create_infos: &'a [DeviceQueueCreateInfo],
    ) -> DeviceCreateInfoBuilder<'a> {...}
    //...
```

Every reference has to live as long as the builder itself. Builders implement `Deref` targeting their corresponding Vulkan struct, so references to builders can be passed directly
to Vulkan functions.

Calling `.build()` will **discard** that lifetime because Vulkan structs use raw pointers internally. This should be avoided as much as possible because this can easily lead to dangling pointers. If `.build()` has to be called, it should be called as late as possible. [Lifetimes of temporaries](https://doc.rust-lang.org/reference/expressions.html#temporary-lifetimes) are extended to the enclosing statement, ensuring they are valid for the duration of a Vulkan call occurring in the same statement.


### Pointer chains

```rust
let mut variable_pointers = vk::PhysicalDeviceVariablePointerFeatures::builder();
let mut corner =
    vk::PhysicalDeviceCornerSampledImageFeaturesNV::builder();
;
let mut device_create_info = vk::DeviceCreateInfo::builder()
    .push_next(&mut corner)
    .push_next(&mut variable_pointers);
```

Pointer chains in builders differ from raw Vulkan. Instead of chaining every struct manually, you instead use `.push_next` on the struct that you are going to pass into the function. Those structs then get *prepended* into the chain.

`push_next` is also type checked, you can only add valid structs to the chain. Both the structs and the builders can be passed into `push_next`. Only builders for structs that can be passed into functions will implement a `push_next`.


### Flags and constants as associated constants

```rust
// Bitflag
vk::AccessFlags::COLOR_ATTACHMENT_READ | vk::AccessFlags::COLOR_ATTACHMENT_WRITE
```

```rust
// Constant
vk::PipelineBindPoint::GRAPHICS,
```
### Debug/Display for Flags

```rust
let flag = vk::AccessFlags::COLOR_ATTACHMENT_READ
        | vk::AccessFlags::COLOR_ATTACHMENT_WRITE;
println!("Debug: {:?}", flag);
println!("Display: {}", flag);
// Prints:
// Debug: AccessFlags(110000000)
// Display: COLOR_ATTACHMENT_READ | COLOR_ATTACHMENT_WRITE
```

### Function pointer loading
Ash also takes care of loading the function pointers. Function pointers are split into 3 categories.

* Entry: Loads the Vulkan library. Needs to outlive `Instance` and `Device`.
* Instance: Loads instance level functions. Needs to outlive the `Device`s it has created.
* Device: Loads device **local** functions.

The loader is just one possible implementation:

* Device level functions are retrieved on a per device basis.
* Everything is loaded by default, functions that failed to load are initialized to a function that always panics.
* Do not call Vulkan 1.1 functions if you have created a 1.0 instance. Doing so will result in a panic.

Custom loaders can be implemented.

### Extension loading
Additionally, every Vulkan extension has to be loaded explicitly. You can find all extensions under [ash::extensions](https://github.com/MaikKlein/ash/tree/master/ash/src/extensions).
```rust
use ash::extensions::khr::Swapchain;
let swapchain_loader = Swapchain::new(&instance, &device);
let swapchain = swapchain_loader.create_swapchain(&swapchain_create_info).unwrap();
```

### Raw function pointers

Raw function pointers are available, if something hasn't been exposed yet in the higher level API. Please open an issue if anything is missing.

```rust
device.fp_v1_0().destroy_device(...);
```

### Support for extension names
```rust
use ash::extensions::{Swapchain, XlibSurface, Surface, DebugReport};
#[cfg(all(unix, not(target_os = "android")))]
fn extension_names() -> Vec<*const i8> {
    vec![
        Surface::name().as_ptr(),
        XlibSurface::name().as_ptr(),
        DebugReport::name().as_ptr()
    ]
}
```

### Implicit handles
Handles from Instance or Device are passed implicitly.
```rust
pub fn create_command_pool(&self,
                           create_info: &vk::CommandPoolCreateInfo)
                           -> VkResult<vk::CommandPool>;

let pool = device.create_command_pool(&pool_create_info).unwrap();
```

### Optional linking

The default `linked` cargo feature will link your binary with the Vulkan loader directly and expose the infallible `Entry::new`.
If your application can handle Vulkan being missing at runtime, you can instead enable the `loaded` feature to dynamically load Vulkan with `Entry::load`.

## Example
You can find the examples [here](https://github.com/MaikKlein/ash/tree/master/examples).
All examples currently require: the LunarG Validation layers and a Vulkan library that is visible in your `PATH`. An easy way to get started is to use the [LunarG Vulkan SDK](https://lunarg.com/vulkan-sdk/)
#### Windows
Make sure that you have a Vulkan ready driver and install the [LunarG Vulkan SDK](https://lunarg.com/vulkan-sdk/).
#### Linux
Make sure that you have a Vulkan ready driver and install the [LunarG Vulkan SDK](https://lunarg.com/vulkan-sdk/). You also have to add the library and layers to your path. Have a look at my [post](http://askubuntu.com/a/803110/77183) if you are unsure how to do that.
#### macOS
Install the [LunarG Vulkan SDK](https://lunarg.com/vulkan-sdk/). This basically entails extracting the downloaded tarball to any location you choose and then setting a few environment variables. Specifically, if `SDK_PATH` is set to the root extracted SDK directory,

* `DYLD_LIBRARY_PATH = $SDK_PATH/macOS/lib`
* `VK_ICD_FILENAMES = $SDK_PATH/macOS/etc/vulkan/icd.d/MoltenVK_icd.json`
* `VK_LAYER_PATH = $SDK_PATH/macOS/etc/vulkan/explicit_layer.d`

### [Triangle](https://github.com/MaikKlein/ash/blob/master/examples/src/bin/triangle.rs)
Displays a triangle with vertex colors.
```
cd examples
cargo run --bin triangle
```

![screenshot](http://i.imgur.com/PQZcL6w.jpg)

### [Texture](https://github.com/MaikKlein/ash/blob/master/examples/src/bin/texture.rs)
Displays a texture on a quad.
```
cd examples
cargo run --bin texture
```
![texture](http://i.imgur.com/trow00H.png)

## Useful resources

### Examples

* [vulkan-tutorial-rust](https://github.com/Usami-Renko/vulkan-tutorial-rust) - A port of [vulkan-tutorial.com](vulkan-tutorial.com).
* [ash-sample-progression](https://github.com/bzm3r/ash-sample-progression) - A port of the LunarG examples.
* [ash-nv-rt](https://github.com/gwihlidal/ash-nv-rt) A raytracing example for ash.

### Utility libraries
* [vk-sync](https://github.com/gwihlidal/vk-sync-rs) - Simplified Vulkan synchronization logic, written in rust.
* [vk-mem-rs](https://github.com/gwihlidal/vk-mem-rs) - This crate provides an FFI layer and idiomatic rust wrappers for the excellent AMD Vulkan Memory Allocator (VMA) C/C++ library.
* [gpu-allocator](https://github.com/Traverse-Research/gpu-allocator) - Memory allocator written in pure Rust for GPU memory in Vulkan and in the future DirectX 12
* [lahar](https://github.com/Ralith/lahar) - Tools for asynchronously uploading data to a Vulkan device.

### Libraries that use ash
* [gfx-rs](https://github.com/gfx-rs/gfx) - gfx-rs is a low-level, cross-platform graphics abstraction library in Rust.

## A thanks to

* [Api with no secrets](https://software.intel.com/en-us/articles/api-without-secrets-introduction-to-vulkan-part-1)
* [Vulkan tutorial](http://jhenriques.net/development.html)
* [Vulkan examples](https://github.com/SaschaWillems/Vulkan)
* [Vulkan tutorial](https://vulkan-tutorial.com/)
* [Vulkano](https://github.com/vulkano-rs/vulkano)
* [vk-rs](https://github.com/Osspial/vk-rs)