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 |
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 |
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.