Firstly, I heavily recommend following the standard Java naming conventions as it will make your code more understandable for others.
The technical name for a block present in the world at a specific position is a "Block State", represented by the BlockState class.
You can only change the block state at a specific position on the server-side. Your raycasting code in ran on the client-side, so you need to use the Fabric Networking API. You can see the server-side Javadoc here and the client-side Javadoc here.
Thankfully, Fabric Wiki has a networking tutorial so you don't have to read all that Javadoc. The part that you're interested in is "sending packets to the server and receiving packets on the server".
Here's a guide specific for your use case:
Introduction to Networking
Minecraft operates in two different components; the client and the server.
The client is responsible for doing jobs such as rendering and GUIs, while the server is responsible for handling the world storage, entity AI etc. (talking about logical client and server here)
The physical server and physical client are the actual JAR files that are run.
The physical (dedicated) server contains only the logical server, while a physical client contains both a logical (integrated) server and a logical client.
A diagram that explains it can be found here.
So, the logical client cannot change the state of the logical server (e.g. block states in a world), so packets have to be sent from the client to the server in order for the server to respond.
The following code is only example code, and you shouldn't copy it! You should think about safety precautions like preventing cheat clients from changing every block. Probably one of the most important rules in networking: assume the client is lying.
The Fabric Networking API
Your starting points are ServerPlayNetworking and ClientPlayNetworking. They are the classes that help you send and receive packets.
Register a listener using registerGlobalReceiver, and send a packet by using send.
You first need an Identifier in order to separate your packet from other packets and make sure it is interpreted correctly. An Identifier like this is recommended to be put in a static field in your ModInitializer or a utility class.
public class MyMod implements ModInitializer {
public static final Identifier SET_BLOCK_PACKET = new Identifier("modid", "setblock");
}
(Don't forget to replace modid with your mod ID)
You usually want to pass data with your packets (e.g. block position and block to change to), and you can do so with a PacketByteBuf.
Let's Piece This all Together
So, we have an Identifier. Let's send a packet!
Client-Side
We will start by creating a PacketByteBuf and writing the correct data:
private static void displayBoundingBox(MatrixStack matrixStack, float tickDelta) {
// ...
PacketByteBuf data = PacketByteBufs.create();
buf.writeBlockPos(hit.getPos());
// Minecraft doesn't have a way to write a Block to a packet, so we will write the registry name instead
buf.writeIdentifier(new Identifier("minecraft", "someblock" /*for example, "stone"*/));
}
And now sending the packet
// ...
ClientPlayNetworking.send(SET_BLOCK_PACKET, buf);
Server-Side
A packet with the SET_BLOCK_PACKET ID has been sent, But we also need to listen and receive it on the server-side. We can do that by using ServerPlayNetworking.registerGlobalReceiver:
@Override
public void onInitialize() {
// ...
// This code MUST be in onInitialize
ServerPlayNetworking.registerGlobalReceiver(SET_BLOCK_PACKET, (server, player, handler, buf, sender) -> {
});
}
We are using a lambda expression here. For more info about lambdas, Google is your friend.
When receiving a packet, code inside your lambda will be executed on the network thread. This code is not allowed to modify anything related to in-game logic (i.e. the world). For that, we will use server.execute(Runnable).
You should read the buf on the network thread, though.
ServerPlayNetworking.registerGlobalReceiver(SET_BLOCK_PACKET, (server, player, handler, buf, sender) -> {
BlockPos pos = buf.readBlockPos(); // reads must be done in the same order
Block blockToSet = Registry.BLOCK.get(buf.readIdentifier()); // reading using the identifier
server.execute(() -> { // We are now on the main thread
// In a normal mod, checks will be done here to prevent the client from setting blocks outside the world etc. but this is only example code
player.getServerWorld().setBlockState(pos, blockToSet.getDefaultState()); // changing the block state
});
});
Once again, you should prevent the client from sending invalid locations
