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88 lines
3.6 KiB
ReStructuredText
88 lines
3.6 KiB
ReStructuredText
.. _doc_openxr_passthrough:
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The OpenXR passthrough
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======================
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Passthrough is a technique where camera images are used to present the environment of the user as the background.
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This turns a VR headset into an AR headset, often referred to as Mixed Reality or MR.
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.. note::
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As passthrough is relatively new there isn't a singular way this is implemented across platforms.
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There may be additions in the future so this is a work in progress.
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Passthrough extension
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---------------------
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OpenXR has a vendor extension for passthrough submitted by Meta.
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Currently this extension is only supported on Quest and PICO but may be adopted by other headsets in the future.
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:ref:`XRInterface <class_xrinterface>` has entry points for passthrough so different interfaces can implement this feature.
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For :ref:`OpenXRInterface <class_openxrinterface>` the meta passthrough extension is implemented here.
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In code you can call ``is_passthrough_supported`` to check if this extension is available.
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If so you can simply enable passthrough by calling ``start_passthrough``.
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You can call ``stop_passthrough`` to disable passthrough.
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You do need to make sure the background is transparent.
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You need to enable the ``transparent_bg`` property on the viewport.
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Some background environment settings will still fill the background with an opaque color,
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you can use a ``custom color`` with a color that has alpha set to 0.
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The OpenXR runtime will display the camera image as the background.
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.. note::
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For privacy reasons **no access** is given to the camera image.
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.. warning::
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After passthrough is enabled it is possible to change settings that will break passthrough.
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Be sure not to disable the ``transparent_bg`` setting or change the environment blend mode.
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This will result in the camera image no longer being visible but you still incur the overhead.
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Always use ``stop_passthrough`` if you wish to turn off passthrough.
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Finally, for using passthrough on the Quest you must set the following export property:
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.. image:: img/xr_export_passthrough.webp
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Passthrough through AR
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----------------------
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Some of the headsets recently adding OpenXR support have taken a different approach.
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They simply mimic being an AR device. The Lynx R1 is such a device but others may be doing the same.
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The following thus applies to both passthrough devices that mimic AR, and actual AR devices.
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If ``is_passthrough_supported`` returns false the next step is to call ``get_supported_environment_blend_modes``.
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This will return a list of supported blend modes for submitting the main render image to OpenXR.
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We need to check if ``XR_ENV_BLEND_MODE_ALPHA_BLEND`` is present in this list.
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If so we can tell OpenXR to expect an image that can be alpha blended with a background.
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To do this, we simply call ``set_environment_blend_mode(xr_interface.XR_ENV_BLEND_MODE_ALPHA_BLEND)``.
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We must also set ``transparent_bg`` to true and adjust the environment to ensure we submit the right image.
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Putting it together
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-------------------
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Putting the above together we can use the following code as a base:
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.. code-block:: gdscript
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func enable_passthrough() -> bool:
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var xr_interface: XRInterface = XRServer.primary_interface
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if xr_interface and xr_interface.is_passthrough_supported():
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if !xr_interface.start_passthrough():
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return false
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else:
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var modes = xr_interface.get_supported_environment_blend_modes()
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if xr_interface.XR_ENV_BLEND_MODE_ALPHA_BLEND in modes:
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xr_interface.set_environment_blend_mode(xr_interface.XR_ENV_BLEND_MODE_ALPHA_BLEND)
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else:
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return false
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get_viewport().transparent_bg = true
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return true
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