New screen behaviour

README.md

@@ -29,6 +29,8 @@ Use `data-projection="plane"` for flat 3D video on a rectangular plane:
 </div>
 ```
 
+Use `data-head-lock="auto|position|none"` to control positional comfort in immersive mode. It defaults to `auto`, which position-locks `vr180` media to the headset to avoid false 6DoF parallax, while leaving `plane` media fixed like a screen. Use `position` to force locking for either projection, or `none` to keep all media world-fixed.
+
 Use an `img` element for a static SBS image:
 
 ```html
@@ -50,7 +52,7 @@ It does not support over-under, MV-HEVC, APMP, or `.aivu`.
 ## How it works
 When the page loads, the media is embedded normally with an entry button over it. When the user clicks the button, the player checks for `navigator.xr` and `immersive-vr` support.
 
-- In WebXR, `vr180` maps the left and right halves of the SBS media onto the matching eyes of a 180 degree sphere.
+- In WebXR, `vr180` maps the left and right halves of the SBS media onto the matching eyes of a 180 degree sphere. In the default `auto` head-lock mode, the sphere follows headset position but not headset rotation.
 - In WebXR, `plane` maps the left and right halves onto the matching eyes of a floating 16:9 plane.
 - Outside WebXR, both modes render only the left half of the SBS media so viewers do not see the raw double image.
 - Static images show only applicable controls; playback, seek, and mute controls are video-only.