feat: add index_camera_passthrough docs

content/docs/fossvr/monado/index_camera_passthrough/_index.md

@@ -0,0 +1,87 @@
+---
+weight: 300
+title: index_camera_passthrough
+---
+
+# index_camera_passthrough
+
+- [index_camera_passthrough GitHub repository](https://github.com/yshui/index_camera_passthrough)
+
+{{< hint danger >}}
+**Warning**
+
+index_camera_passthrough is still to be considered alpha-quality and highly experimental.
+{{< /hint >}}
+
+index_camera_passthrough is a dual API (OpenXR and OpenVR) view corrected passthrough overlay for lighthouse tracked devices with not less or more than 2 external cameras.
+
+Despite the name this application supports all lighthouse style devices as long as two HMD cameras are present and the device has a valid config.json stored on the firmware, factory calibrated with said camera intrinsics.
+
+Currently the overlay is set to toggle off/on with the press of both controller B buttons, at the same time.
+
+Here is an example configuration for monado which should be written to the path `~/.config/index_camera_passthrough/index_camera_passthrough.toml`
+
+For SteamVR usage, change the backend to openvr.
+
+```## This is the configuration file for index_camera_passthrough.
+## This file should live at ~/.config/index_camera_passthrough/index_camera_passthrough.toml
+
+## This is your selected backend
+## possible values: "openxr" | "openvr"
+backend="openxr"
+
+## camera device to use. auto detect if not set
+camera_device = "/dev/video0"
+
+## which button should toggle the overlay visibility. press things
+## button on both controllers to toggle the overlay.
+## possible values: "Menu" | "Grip" | "Trigger" | "A" | "B"
+toggle_button = "B"
+
+## how long does the button need to be held before the overlay open,
+## closing the overlay is always instantaneous
+open_delay = "0s"
+
+[overlay.position]
+## how will the overlay be positioned.
+## possible values:
+##   - "Hmd":      stay in front of your Hmd
+##   - "Absolute": fixed place in VR space
+mode = "Hmd"
+
+## how far away should the overlay be placed
+## only meaningful if mode is "Hmd"
+distance = 0.7
+
+## transformation matrix for absolute position, column-major
+## only meaningful if mode is "Absolute"
+# transform = [ [1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1] ]
+
+[display_mode]
+## the display mode.
+## possible values:
+##   - "Stereo": show a 3D image, how much you can see is limited by how
+##               big the overlay is in your field of view.
+##   - "Flat":   show a flat image
+mode = "Stereo"
+
+## which camera's image to display in Flat mode
+## only meaningful if mode is "Flat"
+# eye = "Left"
+
+## Because your eyes and the cameras are at different physical locations, it is impossible
+## to project camera view into VR space perfectly. There are trade offs approximating
+## this projection.
+##
+## possible values:
+## (a smaller viewing range here means things too close to you will give you double vision).
+##
+##   - "FromCamera": in this mode, we assume your eyes are at the cameras' physical location. this mode 
+##                   has larger viewing range, but everything will look smaller to you.
+##   - "FromEye":    in this mode, we assume your cameras are at your eyes' physical location. everything will
+##                   have the right scale in this mode, but the viewing range is smaller.
+##
+## only available if mode is "Stereo"
+projection_mode = "FromEye"
+
+```