Fix stereo rendering glitches on Meta Quest browsers

Replace camera reference comparison with view matrix eye detection
for more reliable left/right eye identification. Recent Quest Browser
updates (Chromium 138/140, Horizon OS v83) changed WebXR multiview
behavior, causing the previous xrCamera.cameras[0]/[1] comparison
to fail intermittently on the left eye.

The new approach uses activeCamera.matrixWorldInverse.elements[12]
(the X translation in the view matrix) which reliably indicates:
- Negative value = left eye
- Positive value = right eye

This method is consistent across both Quest Browser and Safari/VisionOS.

Also adds explicit video texture synchronization in the render loop
to prevent timing-related glitches.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

vr180player/vr180-player.js

@@ -428,25 +428,20 @@ function init() {
 				return;
 			}
 
-			const xrCamera = renderer.xr.getCamera();
+			// Use view matrix eye offset for reliable stereo detection
+			// This works consistently across Quest Browser updates and Safari/VisionOS
+			// Left eye has negative X offset, right eye has positive X offset
+			const viewMatrix = activeCamera.matrixWorldInverse;
+			const eyeOffsetX = viewMatrix.elements[12];
 
-			if (xrCamera && xrCamera.cameras && xrCamera.cameras.length >= 2) {
+			if (eyeOffsetX < 0) {
-				if (activeCamera === xrCamera.cameras[0]) {
+				// Left eye - show left half of SBS video
 				material.map.offset.x = 0;
-				} else if (activeCamera === xrCamera.cameras[1]) {
-					material.map.offset.x = 0.5;
 			} else {
-					material.map.offset.x = 0;
+				// Right eye - show right half of SBS video
+				material.map.offset.x = 0.5;
 			}
 			material.map.repeat.x = 0.5;
-			} else {
-				const projMatrixEl8 = activeCamera.projectionMatrix.elements[8];
-				if (projMatrixEl8 < -0.0001) {
-					material.map.offset.x = 0; material.map.repeat.x = 0.5;
-				} else if (projMatrixEl8 > 0.0001) {
-					material.map.offset.x = 0.5; material.map.repeat.x = 0.5;
-				}
-			}
 		};
 
 		// Initialize 2D camera
@@ -1731,6 +1726,12 @@ function renderXR(timestamp, frame) {
 		}
 	}
 	try {
+		// Ensure video texture is synchronized with render loop
+		// This prevents glitches from texture update timing issues on Quest browsers
+		if (videoTexture && video && !video.paused && !video.ended) {
+			videoTexture.needsUpdate = true;
+		}
+
 		handleControllerInteractions();
 		renderer.render(scene, camera);
 	} catch (error) {