Update the passthrough documentation to reflect the changes in Godot 4.3

_tools/redirects/redirects.csv

@@ -422,3 +422,4 @@ source,destination
 /tutorials/viewports/viewports.html,/tutorials/rendering/viewports.html
 /contributing/development/compiling/compiling_for_uwp.html,/about/faq.html#which-platforms-are-supported-by-godot
 /tutorials/export/exporting_for_uwp.html,/about/faq.html#which-platforms-are-supported-by-godot
+/tutorials/xr/openxr_passthrough.html,/tutorials/xr/ar_passthrough.html

tutorials/xr/ar_passthrough.rst

@@ -0,0 +1,192 @@
+.. _doc_openxr_passthrough:
+
+AR / Passthrough
+================
+
+Augmented Reality is supported through various methods depending on the capabilities of the hardware.
+
+Headsets such as the Magic Leap and glasses such as TiltFive show the rendered result on
+`see-through displays <https://en.wikipedia.org/wiki/See-through_display>`__ allowing the user
+to see the real world.
+
+Headsets such as the Quest, HTC Elite, and Lynx R1 implement this through a technique called video passthrough,
+where cameras record the real world and these images are used as the background on top of which our rendered
+result is used.
+
+.. note::
+
+    Passthrough is implemented very differently across platforms.
+
+    In Godot 4.3 we have implemented a unified approach that is explained on this help page
+    so you don't need to worry about these differences, the :ref:`XRInterface <class_xrinterface>`
+    implementation is now responsible for applying the correct platform dependent method [#]_.
+
+    For headsets such as the Meta Quest and HTC Elite you will need to use the
+    `OpenXR vendors plugin v3.0.0 <https://github.com/GodotVR/godot_openxr_vendors/releases>`__
+    or later to enable video passthrough.
+
+    For backwards compatibility the old API for passthrough is still available but it is recommended
+    to follow the new instructions below.
+
+Environment blend modes
+-----------------------
+
+The way we configure VR or AR functionality is through setting the environment blend mode.
+This mode determines how the (real world) environment is blended with the virtual world.
+
+.. list-table:: Blend modes
+  :widths: 35 65
+  :header-rows: 1
+
+  * - Blend mode
+    - Description
+  * - XR_ENV_BLEND_MODE_OPAQUE
+    - The rendered image is opaque, we do not see the real world. We're in VR mode.
+      This will turn off passthrough if video-passthrough is used.
+  * - XR_ENV_BLEND_MODE_ADDITIVE
+    - The rendered image is added to the real world and will look semi transparent.
+      This mode is generally used with see-through devices that are unable to obscure
+      the real world.
+      This will turn on passthrough if video-passthrough is used.
+  * - XR_ENV_BLEND_MODE_ALPHA_BLEND
+    - The rendered image is alpha blended with the real world.
+      On see-through devices that support this, the alpha will control the translucency
+      of the optics.
+      On video-passthrough devices alpha blending is applied with the video image.
+      passthrough will also be enabled if applicable. 
+        
+You can set the environment blend mode for your application through the ``environment_blend_mode``
+property of the :ref:`XRInterface <class_xrinterface>` instance.
+
+You can query the supported blend modes on the hardware using the
+``get_supported_environment_blend_modes`` property on the same instance.
+
+Configuring your background
+---------------------------
+
+When setting the blend mode to ``XR_ENV_BLEND_MODE_ALPHA_BLEND`` you must set
+the ``transparent_bg`` property on :ref:`Viewport <class_viewport>` to true.
+When using the ``XR_ENV_BLEND_MODE_ADDITIVE`` blend mode you should set your
+background color to black.
+
+Either solution will result in the background rendering not contributing to lighting.
+It is thus also recommended you adjust your environment settings accordingly and ensure
+there is adequate ambient light set to illuminate your scene.
+
+.. note::
+
+    Some AR SDKs do provide ambient lighting information or even provide a full radiance
+    map to allow for real world reflections in your virtual objects.
+    The core Godot XR functionality doesn't currently have support for this, however this
+    functionality can be exposed through plugins.
+
+OpenXR specific
+---------------
+
+In OpenXR you can configure the default blend mode you want to use.
+Godot will select this blend mode at startup if available.
+If not available Godot will default to the first supported blend mode provided
+by the XR runtime.
+
+.. image:: img/openxr_default_blend_mode.webp
+
+For passthrough devices OpenXR requires additional settings to be configured.
+These settings are platform dependent and provided through the OpenXR vendors plugin.
+
+For example, these are the settings required on Meta Quest:
+
+.. image:: img/openxr_export_passthrough.webp
+
+The ``Passthrough`` setting defines whether passthrough is supported or even required.
+
+The ``Boundary Mode`` allows you to define whether the guardian is needed,
+disabling this fully requires passthrough to be enabled at all times.
+
+Putting it together
+-------------------
+
+Putting the above together we can use the following code as a base:
+
+.. code-block:: gdscript
+
+    @onready var viewport : Viewport = get_viewport()
+    @onready var environment : Environment = $WorldEnvironment.environment
+
+    func switch_to_ar() -> bool:
+        var xr_interface: XRInterface = XRServer.primary_interface
+        if xr_interface:
+            var modes = xr_interface.get_supported_environment_blend_modes()
+            if XRInterface.XR_ENV_BLEND_MODE_ALPHA_BLEND in modes:
+                xr_interface.environment_blend_mode = XRInterface.XR_ENV_BLEND_MODE_ALPHA_BLEND
+                viewport.transparent_bg = true
+            elif XRInterface.XR_ENV_BLEND_MODE_ADDITIVE in modes:
+                xr_interface.environment_blend_mode = XRInterface.XR_ENV_BLEND_MODE_ADDITIVE
+                viewport.transparent_bg = false
+        else:
+            return false
+
+        environment.background_mode = Environment.BG_COLOR
+        environment.background_color = Color(0.0, 0.0, 0.0, 0.0)
+        environment.ambient_light_source = Environment.AMBIENT_SOURCE_COLOR
+        return true
+
+    func switch_to_vr() -> bool:
+        var xr_interface: XRInterface = XRServer.primary_interface
+        if xr_interface:
+            var modes = xr_interface.get_supported_environment_blend_modes()
+            if XRInterface.XR_ENV_BLEND_MODE_OPAQUE in modes:
+                xr_interface.environment_blend_mode = XRInterface.XR_ENV_BLEND_MODE_OPAQUE
+            else:
+                return false
+
+        viewport.transparent_bg = false
+        environment.background_mode = Environment.BG_SKY
+        environment.ambient_light_source = Environment.AMBIENT_SOURCE_BG
+        return true
+
+Shadow to opacity
+-----------------
+
+Shadow to opacity is a render mode for Godot spatial shaders
+that was introduced in Godot 3 specifically for AR.
+It is a special render mode where the more a surface is in shadow,
+the more opaque the surface becomes. When a surface is fully lit,
+the surface becomes fully transparent and thus shows the real world.
+
+However the surface is rendered during the opaque state effectively.
+This has two consequences:
+
+* As both the depth buffer and color buffer are written to, we occlude
+  any geometry behind our surface even when fully transparent.
+* As we are making the surface opaque if in shadow, we can have virtual
+  objects cast shadows on real world objects [#]_.
+
+.. figure:: img/xr_passthrough_example.webp
+    :alt: Image showing shadow to opacity being used to show the users desk.
+
+    Image showing shadow to opacity being used to show the users desk.
+
+This enabled the following use cases:
+
+* You can render a box mesh around a real world table, this ensures the
+  table remains visible even if a virtual object is placed underneath it.
+  The virtual object will be correctly occluded.
+  Placing a virtual object on top of the real world table, will result in
+  a shadow being cast on the table.
+* You can use a shader with this render mode when render a hand mesh
+  using the hand tracking functionality, and ensure your hands properly
+  occlude virtual objects.
+
+The following shader code is a good base for this functionality:
+
+.. code-block:: glsl
+
+    shader_type spatial;
+    render_mode blend_mix, depth_draw_opaque, cull_back, shadow_to_opacity;
+
+    void fragment() {
+        ALBEDO = vec3(0.0, 0.0, 0.0);
+    }
+
+.. [#] Restrictions may apply depending on XR interface implementation.
+.. [#] This feature is still being perfected.

tutorials/xr/index.rst

@@ -18,6 +18,7 @@ Basic Tutorial
    a_better_xr_start_script
    introducing_xr_tools
    basic_xr_locomotion
+   ar_passthrough
 
 Advanced topics
 ---------------
@@ -30,4 +31,3 @@ Advanced topics
    xr_action_map
    xr_room_scale
    openxr_hand_tracking
-   openxr_passthrough

tutorials/xr/openxr_passthrough.rst

@@ -1,87 +0,0 @@
-.. _doc_openxr_passthrough:
-
-The OpenXR passthrough
-======================
-
-Passthrough is a technique where camera images are used to present the environment of the user as the background.
-This turns a VR headset into an AR headset, often referred to as Mixed Reality or MR.
-
-.. note::
-
-  As passthrough is relatively new there isn't a singular way this is implemented across platforms.
-  There may be additions in the future so this is a work in progress.
-
-Passthrough extension
----------------------
-
-OpenXR has a vendor extension for passthrough submitted by Meta.
-Currently this extension is only supported on Quest and PICO but may be adopted by other headsets in the future.
-
-:ref:`XRInterface <class_xrinterface>` has entry points for passthrough so different interfaces can implement this feature.
-For :ref:`OpenXRInterface <class_openxrinterface>` the meta passthrough extension is implemented here.
-
-In code you can call ``is_passthrough_supported`` to check if this extension is available.
-If so you can simply enable passthrough by calling ``start_passthrough``.
-You can call ``stop_passthrough`` to disable passthrough.
-
-You do need to make sure the background is transparent.
-You need to enable the ``transparent_bg`` property on the viewport.
-Some background environment settings will still fill the background with an opaque color,
-you can use a ``custom color`` with a color that has alpha set to 0.
-
-The OpenXR runtime will display the camera image as the background.
-
-.. note::
-
-  For privacy reasons **no access** is given to the camera image.
-
-.. warning::
-
-  After passthrough is enabled it is possible to change settings that will break passthrough.
-  Be sure not to disable the ``transparent_bg`` setting or change the environment blend mode.
-  This will result in the camera image no longer being visible but you still incur the overhead.
-
-  Always use ``stop_passthrough`` if you wish to turn off passthrough.
-
-Finally, for using passthrough on the Quest you must set the following export property:
-
-.. image:: img/xr_export_passthrough.webp
-
-Passthrough through AR
-----------------------
-
-Some of the headsets recently adding OpenXR support have taken a different approach.
-They simply mimic being an AR device. The Lynx R1 is such a device but others may be doing the same.
-
-The following thus applies to both passthrough devices that mimic AR, and actual AR devices.
-
-If ``is_passthrough_supported`` returns false the next step is to call ``get_supported_environment_blend_modes``.
-This will return a list of supported blend modes for submitting the main render image to OpenXR.
-
-We need to check if ``XR_ENV_BLEND_MODE_ALPHA_BLEND`` is present in this list.
-If so we can tell OpenXR to expect an image that can be alpha blended with a background.
-To do this, we simply call ``set_environment_blend_mode(xr_interface.XR_ENV_BLEND_MODE_ALPHA_BLEND)``.
-
-We must also set ``transparent_bg`` to true and adjust the environment to ensure we submit the right image.
-
-Putting it together
--------------------
-
-Putting the above together we can use the following code as a base:
-
-.. code-block:: gdscript
-
-  func enable_passthrough() -> bool:
-    var xr_interface: XRInterface = XRServer.primary_interface
-    if xr_interface and xr_interface.is_passthrough_supported():
-      if !xr_interface.start_passthrough():
-        return false
-    else:
-      var modes = xr_interface.get_supported_environment_blend_modes()
-      if xr_interface.XR_ENV_BLEND_MODE_ALPHA_BLEND in modes:
-        xr_interface.set_environment_blend_mode(xr_interface.XR_ENV_BLEND_MODE_ALPHA_BLEND)
-      else:
-        return false
-
-    get_viewport().transparent_bg = true
-    return true