GaussianContent

GPU-resident container for a single Gaussian-splat 3D Tiles tile. Sealed TileContent variant parallel to MeshContent / PointCloudContent; the GPU buffer slots reflect what a Gaussian-splat renderer needs (positions, anisotropic scales, rotation quaternions, opacity, and either flat RGBA or view-dependent spherical harmonic coefficients).

Lifecycle:

1. prepareGaussianContent runs off the render thread on the parse coroutine, captures per-attribute float arrays, quantizes centres to int16 (for the sort), computes the bounding sphere.

2. syncGaussianContentGpu runs each render frame, looking up each attribute's VBO from the cache and re-uploading the kept-alive payload when LRU eviction has dropped it. After the first sync the float CPU arrays are dropped; the int16 centres + the sort indices stay alive to feed resortByCamera.

3. resortByCamera runs each render frame: launches the bucket sort on Dispatchers.Default when the camera direction has moved past the angle gate, then enqueues the resulting indices for GL upload on the next render frame. Stationary or slow camera pays nothing; in-flight sorts block restart until the upload drains.

A concrete Gaussian-splat codec (earth.worldwind.layer.ogc3d.content.spz.SpzGaussianLoader) produces a GaussianPayload; the built-in rasterizer (earth.worldwind.layer.ogc3d.draw.DrawableTileGaussian) renders the splats as GL_POINTS with a Gaussian falloff per fragment.