A single clipping polygon (up to MAX_CLIP_POLY_VERTS vertices), or null.
When true, a fragment is hidden if it's outside ANY plane (union). When false (the Cesium default), it's hidden only if outside EVERY plane (intersection).
When true, the polygon shows its interior and hides the exterior. When false (the Cesium default), it hides its interior and shows the exterior.
Master switch — when false, pack emits an empty (no-op) uniform.
Re-project the clip geometry into frame's current world frame and return the
packed uniform (a view onto an internal buffer — copy it if you need to retain it).
Call every frame: the floating origin shifts, so the world-space planes/polygon move.
Clipping planes (up to MAX_CLIP_PLANES).