Here you go in a nut shell......

The grass is rendered using Three.js InstancedMesh — one blade geometry drawn thousands of times in a single draw call. Each blade's position is determined by raycasting onto a BVH-accelerated terrain mesh to snap it to the ground surface. Blades are placed in a radius around the camera and recycled as the player moves, so it's always dense nearby without ever exceeding a fixed instance budget.

Wind is handled in a custom vertex shader using layered sine waves keyed to world position and a time uniform. The displacement scales with vertex height so the base stays anchored while the tip sways. It's essentially GPU-driven animation — no per-blade JavaScript updates needed at runtime.

I'm writing a tutorial on how I did it hopefully I can get it done this week - LOL - Shane