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1f35f84e2b
This is for people to review edits for @philiptaylor's points, but I'll probably pull equivalent changes back into the private repo and merge there before bringing it back to github in one of the (hopefully) weekly updates. [ChangeLog] This bundles up low-hanging editorial issues from public issue 101. Some items from that issue are more complex and remain to be done. There's also some related cleanup of the extensions appendix to clarify the distinction between a Vulkan API command, and the functions and function pointers corresponding to that command which may be provided by the API loader and runtime. Remaining todo from #101 : - [ ] 24.5.1 "Ab, Yb, Zb" -> "Xb, Yb, Zb". - [ ] 29.2 "explicitly enabled layers" clarification. - [ ] 30.3.3 Confusingly similar tiny circle symbols in format tables. - [ ] 30.3.3 Missing information about some formats. - [ ] C.3 Clarify or punt on "lower-case UTF-8" in FQDN layer names.
179 lines
7.7 KiB
Plaintext
179 lines
7.7 KiB
Plaintext
// Copyright (c) 2015-2016 The Khronos Group Inc.
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// Copyright notice at https://www.khronos.org/registry/speccopyright.html
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[[initialization]]
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= Initialization
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Before using {apiname}, an application must: initialize it by loading the
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{apiname} commands, and creating a slink:VkInstance object.
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[[initialization-functionpointers]]
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== Command Function Pointers
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{apiname} commands are not necessarily exposed statically on a platform.
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Function pointers for all {apiname} commands can: be obtained with the
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command:
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include::../protos/vkGetInstanceProcAddr.txt[]
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* pname:instance is the instance that the function pointer will be
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compatible with.
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* pname:pName is the name of the command to obtain.
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include::../validity/protos/vkGetInstanceProcAddr.txt[]
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fname:vkGetInstanceProcAddr itself is obtained in a platform- and loader-
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specific manner. Typically, the loader library will export this command as a
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function symbol, so applications can: link against the loader library, or
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load it dynamically and look up the symbol using platform-specific APIs.
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Loaders are encouraged to export function symbols for all other core
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{apiname} commands as well; if this is done, then applications that use only
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the core {apiname} commands have no need to use fname:vkGetInstanceProcAddr.
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Function pointers to commands that don't operate on a specific instance can:
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be obtained by using this command with pname:instance equal to `NULL`. The
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following commands can: be accessed this way:
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* fname:vkEnumerateInstanceExtensionProperties
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* fname:vkEnumerateInstanceLayerProperties
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* fname:vkCreateInstance
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If pname:instance is a valid sname:VkInstance, function pointers to any
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commands that operate on pname:instance or a child of pname:instance can: be
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obtained. The returned function pointer must: only be called with a
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dispatchable object (the first parameter) that is a child of pname:instance.
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If pname:pName is not the name of a core {apiname} command, or is an
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extension command for any extension not supported by any available layer or
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implementation, then fname:vkGetInstanceProcAddr will return `NULL`.
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ifdef::editing-notes[]
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[NOTE]
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.editing-note
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====
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(Jon, Bug 14886 / Gitlab issue 4) The WSI group tentatively agreed that the
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WSI extensions were special, and should get static entry points in link
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libraries and prototypes in +vulkan.h+, while future extensions would have
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to be dynamically loaded. If this decision is upheld by the group as a
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whole, it would probably be encoded in the previous paragraph, in the WSI
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extensions branch of the Specification.
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However, this decision hasn't been fully signed off on by the entire Vulkan
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WG yet AFAIK. Note that implementations typically won't support many of the
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WSI extensions, so ``static entry points'' doesn't relieve apps of the
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neccessity of runtime enabling and testing of each extension before using
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it.
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====
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endif::editing-notes[]
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In order to support systems with multiple {apiname} implementations
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comprising heterogenous collections of hardware and software, the function
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pointers returned by fname:vkGetInstanceProcAddr may: point to dispatch
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code, which calls a different real implementation for different
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sname:VkDevice objects (and objects created from them). The overhead of this
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internal dispatch can: be avoided by obtaining device-specific function
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pointers for any commands that use a device or device-child object as their
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dispatchable object. Such function pointers can: be obtained with the
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command:
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include::../protos/vkGetDeviceProcAddr.txt[]
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* pname:device is the logical device that provides the function pointer.
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* pname:pName is the name of any {apiname} command whose first parameter
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is one of
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** sname:VkDevice
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** sname:VkQueue
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** sname:VkCommandBuffer
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If pname:pName is not the name of one of these {apiname} commands, and is
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not the name of an extension command belonging to an extension enabled for
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pname:device, then fname:vkGetDeviceProcAddr will return `NULL`.
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include::../validity/protos/vkGetDeviceProcAddr.txt[]
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[[initialization-instances]]
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== Instances
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There is no global state in {apiname} and all per-application state is
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stored in a sname:VkInstance object. Creating a sname:VkInstance object
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initializes the {apiname} library and allows the application to pass
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information about itself to the implementation.
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To create an instance object, call:
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include::../protos/vkCreateInstance.txt[]
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* pname:pCreateInfo points to an instance of slink:VkInstanceCreateInfo
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controlling creation of the instance.
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* pname:pAllocator controls host memory allocation as described in the
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<<memory-allocation, Memory Allocation>> chapter.
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* pname:pInstance points a sname:VkInstance handle in which the resulting
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instance is returned.
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include::../validity/protos/vkCreateInstance.txt[]
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The definition of sname:VkInstanceCreateInfo is:
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include::../structs/VkInstanceCreateInfo.txt[]
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* pname:sType is the type of this structure.
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* pname:pNext is `NULL` or a pointer to an extension-specific structure.
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* pname:flags is reserved for future use.
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* pname:pApplicationInfo is `NULL` or a pointer to an instance of
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sname:VkApplicationInfo. If not `NULL`, this information helps
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implementations recognize behavior inherent to classes of applications.
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slink:VkApplicationInfo is defined in detail below.
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* pname:enabledLayerCount is the number of global layers to enable.
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* pname:ppEnabledLayerNames is a pointer to an array of
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pname:enabledLayerCount null-terminated UTF-8 strings containing the
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names of layers to enable for the created instance. See the
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<<extended-functionality-layers,Layers>> section for further details.
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* pname:enabledExtensionCount is the number of global extensions to
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enable.
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* pname:ppEnabledExtensionNames is a pointer to an array of
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pname:enabledExtensionCount null-terminated UTF-8 strings containing the
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names of extensions to enable.
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include::../validity/structs/VkInstanceCreateInfo.txt[]
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fname:vkCreateInstance creates the instance, then enables and initializes
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global layers and extensions requested by the application. If an extension
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is provided by a layer, both the layer and extension must: be specified at
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fname:vkCreateInstance time.
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The pname:pApplicationInfo member of slink:VkInstanceCreateInfo can: point
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to an instance of sname:VkApplicationInfo. This structure is defined as:
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include::../structs/VkApplicationInfo.txt[]
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* pname:sType is the type of this structure.
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* pname:pNext is `NULL` or a pointer to an extension-specific structure.
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* pname:pApplicationName is a pointer to a null-terminated UTF-8 string
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containing the name of the application.
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* pname:applicationVersion is an unsigned integer variable containing the
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developer-supplied version number of the application.
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* pname:pEngineName is a pointer to a null-terminated UTF-8 string
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containing the name of the engine (if any) used to create the
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application.
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* pname:engineVersion is an unsigned integer variable containing the
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developer-supplied version number of the engine used to create the
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application.
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* pname:apiVersion is the version of the {apiname} API against which the
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application expects to run, encoded as described in the
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<<fundamentals-versionnum,API Version Numbers and Semantics>> section.
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If pname:apiVersion is 0 the implementation must: ignore it, otherwise
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if the implementation does not support the requested pname:apiVersion
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it must: return VK_ERROR_INCOMPATIBLE_DRIVER.
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include::../validity/structs/VkApplicationInfo.txt[]
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To destroy an instance, call:
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include::../protos/vkDestroyInstance.txt[]
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* pname:instance is the handle of the instance to destroy.
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* pname:pAllocator controls host memory allocation as described in the
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<<memory-allocation, Memory Allocation>> chapter.
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include::../validity/protos/vkDestroyInstance.txt[]
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