ash/README.md

#Ash

A very lightweight wrapper around Vulkan

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## Stable yet?
I don't expect any big changes anymore. The library will still remain < 1.0 until I had time to use it in a real project. If you encounter any problems, feel free to open an [Issue](https://github.com/MaikKlein/ash/issues).

## Why Ash?
- [x] Lightweight Vulkan wrapper
- [x] Low overhead
- [x] Added type safety
- [x] More convenient to use than raw Vulkan
- [x] Includes a loader
- [x] Extensions have their own loader

## What does it do?

### Explicit returns with `Result`
Functions return a `type VkResult<T> = Result<T, vk::Result>` instead of an error code. No mutable references for the output are required.
```Rust
pub fn create_instance(&self,
                       create_info: &vk::InstanceCreateInfo,
                       allocation_callbacks: Option<&vk::AllocationCallbacks>)
                       -> Result<Instance, InstanceError> {
let instance: Instance = entry.create_instance(&create_info, None)
    .expect("Instance creation error");
```


Always returns a `Vec<T>` for functions that output multiple values.
```Rust
pub fn get_swapchain_images_khr(&self,
                                swapchain: vk::SwapchainKHR)
                                -> VkResult<Vec<vk::Image>>;
let present_images = swapchain_loader.get_swapchain_images_khr(swapchain).unwrap();
```

### Slices
Ash always uses slices in functions.
```Rust
// C
void vkCmdPipelineBarrier(
    VkCommandBuffer                             commandBuffer,
    VkPipelineStageFlags                        srcStageMask,
    VkPipelineStageFlags                        dstStageMask,
    VkDependencyFlags                           dependencyFlags,
    uint32_t                                    memoryBarrierCount,
    const VkMemoryBarrier*                      pMemoryBarriers,
    uint32_t                                    bufferMemoryBarrierCount,
    const VkBufferMemoryBarrier*                pBufferMemoryBarriers,
    uint32_t                                    imageMemoryBarrierCount,
    const VkImageMemoryBarrier*                 pImageMemoryBarriers);

// 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]);

device.cmd_pipeline_barrier(setup_command_buffer,
                            vk::PIPELINE_STAGE_TOP_OF_PIPE_BIT,
                            vk::PIPELINE_STAGE_TOP_OF_PIPE_BIT,
                            vk::DependencyFlags::empty(),
                            &[],
                            &[],
                            &[layout_transition_barrier]);

// or

let slice = device.map_memory::<Vertex>(vertex_input_buffer_memory,
                          0,
                          vertex_input_buffer_info.size,
                          vk::MemoryMapFlags::empty())
    .unwrap();
slice.copy_from_slice(&vertices);
```

### Type safety
Ash still uses raw Vulkan structs. The only difference is type safety. Everything that can be an enum is an enum like `vk::StructureType`, flags are implemented similar to the `Bitflags` crate. Ash also follows the Rust style guide. The reason that Ash uses raw Vulkan structs is to be extensible, just like the Vulkan spec.
```Rust
let pool_create_info = vk::CommandPoolCreateInfo {
    s_type: vk::StructureType::CommandPoolCreateInfo,
    p_next: ptr::null(),
    flags: vk::COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT,
    queue_family_index: queue_family_index,
};
let pool = device.create_command_pool(&pool_create_info, None).unwrap();
```

Additionally pointers like `Instance`, `Device`, `Queue` etc are hidden behind a type. Those pointers can only be constructed from within `Ash` which elimites invalid API usage and has the benefit of making some functions in Vulkan **safe**.

### Function pointer loading
Ash also takes care of loading the function pointers. Function pointers are split into 3 categories. Entry, Instance and Device. The reason for not loading it into a global is that in Vulkan you can have multiple devices and each device must load its own function pointers.
```Rust
// Looks for the vulkan lib in your path, alternatively you can supply the path explicitly.
let entry = Entry::load_vulkan().unwrap();
let instance: Instance = entry.create_instance(&create_info).expect("Instance creation error");
let device: Device = instance.create_device(pdevice, &device_create_info)
    .unwrap();
```

### Extension loading
Additionally, every Vulkan extension has to be loaded explicity. You can find all extensions under [ash::extensions](https://github.com/MaikKlein/ash/tree/master/src/extensions). You still have to tell Vulkan which instance or device extensions you want to load.
```Rust
use ash::extensions::Swapchain;
let swapchain_loader = Swapchain::new(&instance, &device).expect("Unable to load swapchain");
let swapchain = swapchain_loader.create_swapchain_khr(&swapchain_create_info).unwrap();
```

### Implicit handles
You don't have to pass an Instance or Device handle anymore, this is done implicitly for you. This makes sure that you will always use the most optimal implementation for your `Device`.
```Rust
// C
VkResult vkCreateCommandPool(
    VkDevice                                    device,
    const VkCommandPoolCreateInfo*              pCreateInfo,
    const VkAllocationCallbacks*                pAllocator,
    VkCommandPool*                              pCommandPool);

// Rust
pub fn create_command_pool(&self,
                           create_info: &vk::CommandPoolCreateInfo)
                           -> VkResult<vk::CommandPool>;

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

### 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()
    ]
}
```
## 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 start is to use the [LunarG Vulkan SDK](https://lunarg.com/vulkan-sdk/)
### [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)

## Roadmap

### Extensions
- [x] Swapchain
- [x] Surface
- [x] XlibSurface
- [x] DebugReport
- [x] Win32Surface
- [x] MirSurface
- [x] XcbSurface
- [x] AndroidSurface
- [x] WaylandSurface
- [ ] Display

### In progress
- Wrapping the complete spec

## 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://av.dfki.de/~jhenriques/development.html)
* [Vulkan examples](https://github.com/SaschaWillems/Vulkan)
* [Vulkan tutorial](https://vulkan-tutorial.com/)
* [Vulkano](https://github.com/tomaka/vulkano/)
* [vk-rs](https://github.com/Osspial/vk-rs)