Struct vulkano::instance::Instance[−][src]

pub struct Instance { /* fields omitted */ }

Expand description

An instance of a Vulkan context. This is the main object that should be created by an application before everything else.

Application info

When you create an instance, you have the possibility to pass an ApplicationInfo struct as the first parameter. This struct contains various information about your application, most notably its name and engine.

Passing such a structure allows for example the driver to let the user configure the driver’s behavior for your application alone through a control panel.

use vulkano::instance::{Instance, InstanceExtensions};
use vulkano::Version;

// Builds an `ApplicationInfo` by looking at the content of the `Cargo.toml` file at
// compile-time.
let app_infos = app_info_from_cargo_toml!();

let _instance = Instance::new(Some(&app_infos), Version::V1_1, &InstanceExtensions::none(), None).unwrap();

API versions

Both an Instance and a Device have a highest version of the Vulkan API that they support. This places a limit on what Vulkan functions and features are available to use when used on a particular instance or device. It is possible for the instance and the device to support different versions. The supported version for an instance can be queried before creation with FunctionPointers::api_version, while for a device it can be retrieved with PhysicalDevice::api_version.

When creating an Instance, you have to specify a maximum API version that you will use. This restricts the API version that is available for the instance and any devices created from it. For example, if both instance and device potentially support Vulkan 1.2, but you specify 1.1 as the maximum API version when creating the Instance, then you can only use Vulkan 1.1 functions, even though they could theoretically support a higher version. You can think of it as a promise never to use any functionality from a higher version.

The maximum API version is not a minimum, so it is possible to set it to a higher version than what the instance or device inherently support. The final API version that you are able to use on an instance or device is the lower of the supported API version and the chosen maximum API version of the Instance.

However, due to a quirk in how the Vulkan 1.0 specification was written, if the instance only supports Vulkan 1.0, then it is not possible to specify a maximum API version higher than 1.0. Trying to create an Instance will return an IncompatibleDriver error. Consequently, it is not possible to use a higher device API version with an instance that only supports 1.0.

Extensions

When creating an Instance, you must provide a list of extensions that must be enabled on the newly-created instance. Trying to enable an extension that is not supported by the system will result in an error.

Contrary to OpenGL, it is not possible to use the features of an extension if it was not explicitly enabled.

Extensions are especially important to take into account if you want to render images on the screen, as the only way to do so is to use the VK_KHR_surface extension. More information about this in the swapchain module.

For example, here is how we create an instance with the VK_KHR_surface and VK_KHR_android_surface extensions enabled, which will allow us to render images to an Android screen. You can compile and run this code on any system, but it is highly unlikely to succeed on anything else than an Android-running device.

use vulkano::instance::Instance;
use vulkano::instance::InstanceExtensions;
use vulkano::Version;

let extensions = InstanceExtensions {
    khr_surface: true,
    khr_android_surface: true,
    .. InstanceExtensions::none()
};

let instance = match Instance::new(None, Version::V1_1, &extensions, None) {
    Ok(i) => i,
    Err(err) => panic!("Couldn't build instance: {:?}", err)
};

Layers

When creating an Instance, you have the possibility to pass a list of layers that will be activated on the newly-created instance. The list of available layers can be retrieved by calling the layers_list function.

A layer is a component that will hook and potentially modify the Vulkan function calls. For example, activating a layer could add a frames-per-second counter on the screen, or it could send information to a debugger that will debug your application.

Note: From an application’s point of view, layers “just exist”. In practice, on Windows and Linux, layers can be installed by third party installers or by package managers and can also be activated by setting the value of the VK_INSTANCE_LAYERS environment variable before starting the program. See the documentation of the official Vulkan loader for these platforms.

Note: In practice, the most common use of layers right now is for debugging purposes. To do so, you are encouraged to set the VK_INSTANCE_LAYERS environment variable on Windows or Linux instead of modifying the source code of your program. For example: export VK_INSTANCE_LAYERS=VK_LAYER_LUNARG_api_dump on Linux if you installed the Vulkan SDK will print the list of raw Vulkan function calls.

Example

// For the sake of the example, we activate all the layers that
// contain the word "foo" in their description.
let layers: Vec<_> = instance::layers_list()?
    .filter(|l| l.description().contains("foo"))
    .collect();

let layer_names = layers.iter()
    .map(|l| l.name());

let instance = Instance::new(None, Version::V1_1, &InstanceExtensions::none(), layer_names)?;

Struct vulkano::instance::Instance[−][src]

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