This is a more conceptual, thinking-out-loud question than a technical one. I have a 3D heightmapped terrain as part of a multiplayer RTS that I would like to terraform over a network. The terraforming will be done by units within the gameworld; the player will paint a "target heightmap" that they'd like the current terrain to resemble and units will deform towards that on their own (a la Perimeter).

Given my terrain is 257x257 vertices, the naive approach of sending heights when they change will flood the bandwidth very quickly - updating a quarter of the terrain every second will hit ~66kB/s. This is clearly way too much.

My next thought was to move to a brush-based system, where you send e.g. the centre of a circle, its radius, and some function defining the influence of the brush from the centre going outwards. But even with reliable UDP the "start" and "stop" messages could still be delayed. I guess I could compare timestamps and compensate for this, although it'd likely mean that clients would deform verts too much on their local simulations and then have to smooth them back to the correct heights. I could also send absolute vert heights in the "start" and "stop" messages to guarantee correct data on the clients.

Alternatively I could treat brushes in a similar way to units, and do the standard position + velocity + client-side prediction jazz on them, with the added stipulation that they deform terrain within a certain radius around them. The server could then intermittently do a pass and send (a subset of) recently updated verts to clients as and when there's bandwidth to spare.

Any other suggestions, or indications that I'm on the right (or wrong!) track with any of these ideas would be greatly appreciated.