OpenXR 0.90 Overview Guide
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OpenXR is a cross-platform API that enables combined real and virtual environments through human-machine interaction, including virtual reality, augmented reality, and mixed reality technologies. The document provides a high-level overview of key concepts in OpenXR, including instances, sessions, spaces, swapchains, input and haptics, and the render loop. It also summarizes how OpenXR separates applications actions from input devices and uses interaction profiles to map actions to inputs.
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OpenXR 0.90 Overview Guide
- 1. Input and Haptics OpenXR API Overview Instances GetInstanceProcAddr EnumerateInstanceExtensionProperties CreateInstance DestroyInstance GetInstanceProperties Sessions CreateSession BeginSession EndSession DestroySession OpenXRTM is a cross-platform API that enables a continuum of real-and-virtual combined environments generated by computers through human-machine interaction and is inclusive of the technologies associated with virtual reality, augmented reality, and mixed reality. More information and specifications at khronos.org/openxr API Layers Various layers can be enabled to enhance functionality such as a validation layer, or tracing layer. Input and Haptics Applications define actions, the runtime binds actions to input devices. Action sets are application-defined collections of actions. Instances Application’s representation of the OpenXR runtime. The CreateInstance function calls the loader to determine which installed OpenXR runtime to connect to. View Configurations Configuration for rendering, such as MONO or STEREO. The application queries the runtime for supported configurations, then selects the configuration to use. Systems A collection of related devices in the runtime working together to enable XR experiences. May include VR/AR displays, input form factors, and trackable objects. Swapchains The OpenXR runtime allows applications to create multiple swapchains, into which 2D or 3D images are organized to present to the user. Render Loop A session is created and the application’s XR rendering loop begins. Sessions An active interaction between the application and the runtime. An application indicates it wants to render by beginning a session. Spaces Frame of reference, how to track real and virtual objects and their relative motion. OpenXR defines 3 reference spaces, VIEW, LOCAL, and STAGE. Events Events are messages sent from the runtime into a queue from which the application will read one at a time. Helper Functions Functions to help with conversions of strings. Events PollEvent Systems GetSystem GetSystemProperties EnumerateEnvironmentBlendModes API Layers EnumerateApiLayerProperties View Configurations EnumerateViewConfigurations GetViewConfigurationProperties EnumerateViewConfigurationViews LocateViews Helper Functions ResultToString StructureTypeToString StringToPath PathToString Create action and action spaces xrCreateAction name = “teleport” type = XR_INPUT_ACTION_TYPE_BOOLEAN name = “teleport_ray” type = XR_INPUT_ACTION_TYPE_POSE xrCreateActionSpace action = “teleport_ray” Render Loop WaitFrame BeginFrame EndFrame Input and Haptics CreateAction DestroyAction CreateActionSet DestroyActionSet GetActionState* SyncActionData GetBoundSourceForAction GetInputSourceLocalizedName SetInteractionProfileSuggestedBindings GetCurrentInteractionProfile ApplyHapticFeedback StopHapticFeedback Swapchains EnumerateSwapchainFormats CreateSwapchain DestroySwapchain EnumerateSwapchainImages AcquireSwapchainImage WaitSwapchainImage ReleaseSwapchainImage Spaces EnumerateReferenceSpaces CreateReferenceSpace CreateActionSpace LocateSpace GetReferenceSpaceBoundsRect DestroySpace OpenXR separates the application actions such as Move, Jump, and Teleport from the input device: Trigger, Thumbstick, and Button. This simplifies support for different or future input devices and maximizes user accessibility. Interaction profiles identify a collection of buttons and other input sources in a physical arrangement to allow applications and runtimes to coordinate action to input mapping. Interaction profiles for well known XR systems are included in the specification. Set up interaction profile bindings xrSetInteractionProfileSuggestedBindings /interaction_profiles/oculus/touch_controller Action “teleport” -> /user/hand/right/input/a/click Action “teleport_ray” -> /user/hand/right/input/pointer/pose /interaction_profiles/htc/vive_controller Action “teleport” -> /user/hand/right/input/trackpad/click Action “teleport_ray” -> /user/hand/right/input/pointer/pose Get action states xrGetActionStateBoolean (“teleport_ray”) if (state.currentState) // button is pressed { xrLocateSpace (teleport_ray_space, stage_reference_space); }
- 2. Learn more about OpenXR OpenXR is maintained by the Khronos® Group, a worldwide consortium of organizations that creates and maintains key standards used across many industries. Visit Khronos online for resources to help you master OpenXR: OpenXR Resource Page: khronos.org/openxr Forums: forums.khronos.org Slack: https://khr.io/slack Videos & Presentations: khr.io/library Khronos Events: khronos.org/events Khronos Blog: khronos.org/blog Reference Guides: khr.io/refguides Khronos Books: khronos.org/developers/books Khronos Merchandise: khronos.org/store © 2019 The Khronos® Group Inc. OpenXR Application Lifecycle A high level overview of a typical OpenXR application including the order of function calls, creation of objects, session state changes, and the rendering loop. Refer to the OpenXR specification at khronos.org/openxr for details. www.khronos.org/openxr Session States and Frame Loop Applica�on Started Decide API and Extensions usages Instance Created Instance Destroyed Applica�on Completed Session System Unavailable System Available Session Created Session Destroyed xrDestroyInstance xrCreateInstance xrGetInstanceProperties xrEnumerateApiLayerProperties xrEnumerateExtensionProperties xrCreateSession xrDestroySession xrDestroySpace xrDestroyAction xrDestroyActionSet xrDestroySwapchain xrGetSystem XR_ERROR _FORM_FACTOR_UNAVAILABLE xrPollEvent xrGetSystemProperties xrEnumerateViewConfigurations xrGetViewConfigurationProperties xrEnumerateViewConfigurationViews xrEnumerateEnvironmentBlendModes XR_SESSION_STATE RUNNING or VISIBLE or FOCUSED Execute Graphics Work xrReleaseSwapchainImage xrAcquireSwapchainImage xrWaitSwapchainImage xrLocateSpace xrLocateViews xrSyncActionData xrGetActionState* xrApplyHapticFeedback xrStopHapticFeedback xrGetCurrentInteractionProfile XR_SESSION_STATE READY XR_SESSION_STATE STOPPING XR_SESSION_STATE EXITING XR_SESSION_STATE LOSS_PENDING not focused XR_SESSION_STATE IDLE xrWaitFrame xrBeginFrame not visible xrEnumerateReferenceSpaces xrCreateReferenceSpace xrCreateActionSpace xrGetReferenceSpaceBoundsRect xrEnumerateSwapchainFormats xrCreateSwapchain xrEnumerateSwapchainImages xrCreateActionSet xrCreateAction xrSetInteractionProfileSuggestedBindings xrEndFrame xrBeginSession xrEndSession Handle Ac�ons