enableBackgroundFromAsset method
Enables the background using an asset image.
Implementation
Future<void> enableBackgroundFromAsset(String assetPath) async {
_bg ??= SkyPass(assetPath: assetPath);
await _bg!.init(_gl, caps: _caps);
_bg?.setYawPitchDegrees(90, 0); // pitch only → flips sky/ground
_bgAssetPath = assetPath;
}