Engine/Structure

The base (NMPR)

Everything is built on a small core, that was the original network multiplayer release of Minetest (call it NMPR). Being around 8000 lines of code, it contains:

• The map, including simple voxel lighting and rendering code
• The client + server logic
• The main loop, invoking the client, the server and the rendering.
• A bunch of wrappers for OS-dependent things, and utilities.

As the current code still largely bases on the NMPR, it is useful to look at how it works.

Map (the voxels)

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Network protocol

The high-level network protocol of NMPR is delightfully simple. There are three commands for the server, and three commands for the client. Since this, a lot has been added and changed, but the basic idea stays the same.

Server -> Client

TOCLIENT_BLOCKDATA	v3s16 p, MapBlock data	Send the content of a block (16x16x16 nodes)
TOCLIENT_ADDNODE	v3s16 p, MapNode node	Add a node
TOCLIENT_REMOVENODE	v3s16 p, MapNode node	Remove a node
TOCLIENT_PLAYERPOS	foreach(player){ u16 player_id, v3s32 p*100, v3s32 speed*100}	Update players on client

Client -> Server

TOSERVER_GETBLOCK	v3s16 p	Ask the server to send the data of a block
TOSERVER_ADDNODE	v3s16 p, MapNode node	Inform the server of a placed node
TOSERVER_REMOVENODE	v3s16 p, MapNode node	Inform the server of a removed node
TOSERVER_PLAYERPOS	v3s32 p*100, v3s32 speed*100	Inform the server of the positon of the local player

Minetest uses it's own reliability layer on top of UDP. It isn't well documented at the moment, and thorough understanding of it isn't that important, so let's skip it as of now.

Rendering

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Programming style

Minetest is designed in a fairly basic C++ object oriented way: Almost everything is contained within some kind of a class, with inheritance and interfaces being used sparingly in obvious ways.