Event Handling

[modwizcode]

Can you explain that a bit more? I’m pretty new to low level java like this, so I’m trying to learn it. What are mixins exactly? I’ve looked at that file before, but I’m not sure what exactly it’s doing. How do I match up the arguments for the events?

[thomas15v]

Mixins make it possible to change minecraft base classes without writing the bytecode. Sponge uses mixins because managing bytecode is not funny and maintainable. Also you will have to change brand if you want to use them.

It may be better if you read the description on the example file for mixins:
https://github.com/SpongePowered/Sponge/blob/feature/mixins/src/main/java/org/spongepowered/mixin/impl/MixinWorld.java

Also when playing with mixins don’t forget to register your mixing class here:
https://github.com/SpongePowered/Sponge/blob/feature/mixins/src/main/resources/mixins.sponge.json

[modwizcode]

Ah thanks, very helpful. We should keep a post like this pinned for people who want to start working on this. No need to duplicate this effort.

[modwizcode]

Also mixins aren’t part of sponge by default, it’s still in a branch, any reason for this?

[thomas15v]

I wouldn’t know I am not a Sponge Dev . I suppose they made this feature on a different branch because they where unsure how they would do it.

Also its on PR, But I would be surprised if it doesn’t get accepted.

Implement CatalogType ingore case. Closes #59 #60

[modwizcode]

I just started messing around with the pre-existing event mapping stuff, but lets say I wanted to make a command listening event that just forwarded the whole string to the event handler. How would I map the methods to the forge event? Sorry about all the questions, I’ve never really looked into this class mapping and ASM stuff.

[thomas15v]

@modwizcode

How would I map the methods to the forge event?

events.put("net.minecraftforge.event.ServerChatEvent", AsyncPlayerChatEvent.class);

Seems you are unaware of the selection ability of gist xD. What is fine it also took me a while to notice it. If you click the link you will see that line 70 is selected .

[modwizcode]

And then if I needed to modify the forge event to fit the Sponge event? Do I have to use mixins to do that?

[thomas15v]

Yes for the methods you need a mixin I guess. I wrote a mixin class to explain (not tested, but this is as it should work). Be aware that you don’t need to implement methods from the Event class. The event transformer already implement those.

package org.spongepowered.mixin.impl;

import net.minecraft.entity.player.EntityPlayerMP;
import net.minecraftforge.event.ServerChatEvent;
import org.spongepowered.api.entity.Player;
import org.spongepowered.api.event.player.AsyncPlayerChatEvent;
import org.spongepowered.mod.mixin.Mixin;
import org.spongepowered.mod.mixin.Shadow;


@Mixin(ServerChatEvent.class)
public abstract class MixinServerChatEvent implements AsyncPlayerChatEvent {

    @Shadow public String message;
    @Shadow public EntityPlayerMP player;
    
    @Override
    public String getMessage() {
        return message; //this will work
    }

    @Override
    public Player getPlayer() {
        return (Player) player; //This will crash until Player has a mixin 
    }
} 

[modwizcode]

Awesome thanks, I can’t wait for Mixins to become core.

[thomas15v]

Me either xD. But ya they are waiting on Forge 1.8. As it is unknown of the events will still be there (I suppose they will).

Also note: For the chat event this implementation is wrong. Because the event should be asynchronous.

[modwizcode]

Finally got the chat event to work without mixins. Turns out I have to add the registration in two places to get it to be ASM transformed.

[modwizcode]

Now I just want to know what the BlockEvent class visitor is doing.

[thomas15v]

@modwizcode

BlockEvent class visitor

Sorry I can’t find that part.

[modwizcode]

https://github.com/SpongePowered/Sponge/blob/master/src/main/java/org/spongepowered/mod/asm/util/ASMEventListenerHolderFactory.java

You’ll have to open the truncated file, but this is the file.

[thomas15v]

Honestly no idea what it is doing. Looks hacky. Meaby @Raphfrk could explain it?

[modwizcode]

I would like it to be explained, mixins were merged in to master yesterday and I finally think I have ASM figured out.

[modwizcode]

Found some of what I needed here

Looking for sage advice on Access Transformer and bytecode injection

The problem it solves is that BlockBreak is a forge event, and because of that it can’t be exposed to the sponge API. But we do have a VoxelEvent in the API. So for the sponge implementation we either need to duplicate the BlockBreak event(by inserting the event posts for VoxelEvent at the correct positions, potentially breaking stuff and separating the forge mods from sponge plugins) or to extend the BreakBlock event so that it functions as a VoxelEvent. For the other events currently named …

But I still don’t know why that one particular class is modified in that specific place, while the startup and initialization events are injected as part of the EventTransformer class.

[modwizcode]

The solution for this currently won’t work with Mixins because of this issue:

Damageable interface clashes with required extend EntityPlayer for Player Mixin

Both Bukkit and Sponge have chosen to implement damage as a double instead of the default implementation of an float. What this means is that when attempting to create a Mixin for the Player or Entity interfaces, which requires both implementing the Sponge interface and extending the Forge/Minecraft class, that it won’t be possible to implement anything using the Damageable interface. I may be mistaken and it might be a simple workaround that I’m missing, but I can’t seem to figure it out.

[modwizcode]

As I am wrapping up finished posts, this was fixed by mixins with the annotations.