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Diffstat (limited to 'loader/LoaderAndLayerInterface.md')
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diff --git a/loader/LoaderAndLayerInterface.md b/loader/LoaderAndLayerInterface.md index 3f0fef86..ca71fae5 100644 --- a/loader/LoaderAndLayerInterface.md +++ b/loader/LoaderAndLayerInterface.md @@ -248,6 +248,66 @@ Get\*ProcAddr will often be the only way to access extension API features.  +##### WSI Extensions + +Khronos approved WSI extensions are available and provide Windows System Integration +support for various execution environments. It is important to understand that some WSI +extensions are valid for all targets, but others are particular to a given execution +environment (and loader). This desktop loader (currently targeting Windows and Linux) +only enables those WSI extensions that are appropriate to the current environment. +For the most part, the selection is done in the loader using compile-time preprocessor +flags. All versions of the desktop loader currently expose at least the following WSI +extension support: +- VK_KHR_surface +- VK_KHR_swapchain +- VK_KHR_display + +In addition, each of the following OS targets for the loader support target-specific extensions: +- **Windows** : VK_KHR_win32_surface +- **Linux (default)** : VK_KHR_xcb_surface and VK_KHR_xlib_surface +- **Linux (Wayland build)** : VK_KHR_wayland_surface +- **Linux (Mir build)** : VK_KHR_mir_surface + +**NOTE:** Wayland and Mir targets are not fully supported at this time and should be considered +alpha quality. + +It is important to understand that while the loader may support the various entry-points +for these extensions, there is a hand-shake required to actually use them: +* At least one physical device must support the extension(s) +* The application must select such a physical device +* The application must request the extension(s) be enabled while creating the instance or logical device (This depends on whether or not the given extension works with an instance or a device). +* The instance and/or logical device creation must succeed. + +Only then can you expect to properly use a WSI extension in your Vulkan program. + +##### New Extensions + +With the ability to expand Vulkan so easily, extensions will be created that the loader knows +nothing about. If the extension is a device extension, the loader will pass the unknown +entry-point down the device call chain ending with the appropriate ICD entry-points. +However, if the extension is an instance extension, the loader will fail to load it. + +*But why doesn't the loader support unknown instance extensions?* +<br/> +Let's look again at the Instance call chain: + + +Notice that for a normal instance function call, the loader has to handle passing along the +function call to the available ICDs. If the loader has no idea of the parameters or return +value of the instance call, it can't properly pass information along to the ICDs. +There may be ways to do this, which will be explored in the future. However, for now, this +loader does not support any unknown instance extensions. + +Because the device call-chain does not pass through the loader terminator, this is not +a problem for device extensions. Instead, device extensions terminate directly in the +ICD they are associated with. + +*Is this a big problem?* +<br/> +No! Most extension functionality only affects a device and not an instance or a physical +device. Thus, the overwhelming majority of extensions will be device extensions rather than +instance extensions. + Vulkan Installable Client Driver interface with the loader ---------------------------------------------------------- |