[1.10.2][SOLVED] Modifying a vanilla method

[yooksi]

What would be the easiest way of successfully modifying a vanilla method? I would like all calls coming to method A to be diverted to method B (which would be a custom method). If I could modify the method at runtime I would inject some code that just makes a call to method B, don't know if it works like that in reality. After searching online about this I've found out this is called reflection and that it's a very advanced procedure. However I've seen some mods around that have done exactly that, but I am having problems getting a grasp on how they did it. As always, any help would really be appreciated, thanks!

[Animefan8888]

What would be the easiest way of successfully modifying a vanilla method? I would like all calls coming to method A to be diverted to method B (which would be a custom method). If I could modify the method at runtime I would inject some code that just makes a call to method B, don't know if it works like that in reality. After searching online about this I've found out this is called reflection and that it's a very advanced procedure. However I've seen some mods around that have done exactly that, but I am having problems getting a grasp on how they did it. As always, any help would really be appreciated, thanks!

Modifying a vanilla method is not supported by forge or this forum as that requires editing base classes which is a coremod.

[swordkorn]

I don't think he's asking how to edit the base code so to speak.

 

It would depend on which behaviours you intended to implement/"override" really. Using @SubscribeEvent and writing custom event handlers to "add" or "tweak" some existing Minecraft behaviour could give the illusion of overriding base methods, but is far simpler than trying to reflect the code.

[jeffryfisher]

I would like all calls coming to method A to be diverted to method B...

*IF* method 'A' happens to have a Forge hook in it, then you can see what event it spawns and write an event handler (method 'B') whose result can cause the remainder of method 'A' to be skipped.

 

If not, then you probably can't get there from here.

 

Which method do you want to hijack?

[Draco18s]

And why

[yooksi]

Modifying a vanilla method is not supported by forge or this forum as that requires editing base classes which is a coremod.

I do not wish to create a coremod, I would like to modify the content of the vanilla method during application runtime. There is a forum thread about a similar idea here, and it recommends using Access Transformers. Maybe what I am doing is considered creating a coremod, but this is not my intention.

 

There is no single way to achieve this. Modifying the actual code of vanilla classes is not possible as was said above.

Please describe what you want to achieve (describe the behavior, not how you intend to code it!).

I would like to replicate what the developer called atomicstrykers did here. He was able to redirect all calls coming from World.getRawLight to his own custom method, and like that was able to control all the light values in World. The reason I am interested in this is because I would like to create a moving light source that moves with the player, like an item torch emitting light when held for example. What makes me worry about this is the optimization side, so would the way he did it be a better approach then manually setting the light values and sending them to world for update?

[Draco18s]

Modifying a vanilla method is not supported by forge or this forum as that requires editing base classes which is a coremod.

I do not wish to create a coremod, I would like to modify the content of the vanilla method during application runtime. There is a forum thread about a similar idea here, and it recommends using Access Transformers. Maybe what I am doing is considered creating a coremod, but this is not my intention.

 

Access Transformers are....

• A coremod
  
• Completely unnecessary as you can use Reflection
  
• Don't modify code, only the access level (public, private, protected).

[yooksi]

I don't think an effect similar to DynamicLights is possible without a coremod at this time, so go ahead and investigate where exactly you need forge hooks inserted (as little as possible) and then submit a pull request. If the hooks make sense, it will go in.

Thanks for the advice, I will take a look at Forge's code and see where I could insert one.

 

Modifying a vanilla method is not supported by forge or this forum as that requires editing base classes which is a coremod.

I do not wish to create a coremod, I would like to modify the content of the vanilla method during application runtime. There is a forum thread about a similar idea here, and it recommends using Access Transformers. Maybe what I am doing is considered creating a coremod, but this is not my intention.

 

Access Transformers are....

• A coremod
  
• Completely unnecessary as you can use Reflection
  
• Don't modify code, only the access level (public, private, protected).

Is it possible to do what I want to do with reflection then?

[Draco18s]

Is it possible to do what I want to do with reflection then?

 

Unlikely.  But I don't know what it is you are trying to do.

[Elix_x]

In some cases when method has no forge hooks, or other clear way of taking over calls, there is a an option that might* work if:

-Method is NOT static.

-Method is NOT private.

-Method is NOT final.

-Class is NOT final.

-You have / can gain access to classes' all instances.

 

When all of these (maybe not the * one, more about it in a second) are the case for you, you can create a class extending class that has the method and override it. Then what you have to do is replace all instances of class in question with your instance. It's easy if class is used as singleton, might be a bit harder if there are multiple instaces of it (but at that point, you always have a forge hook that allows accessing all/part of these instances).

Remember a few things though:

-Inner classes are not a problem, you'll just have to repeat process with its' external classes.

-If the instance(s) is/are stored in a private or final field, that's not a problem either. You have a way around both with reflection,

-If you have to default to vanilla(?) in overriden method, store instance that you replace and call it's method. It's very important, as other wise if other mods also use same replacement way...

 

*-If there are multiple mods using this way for the same thing, and one of them does not do it properly, it will break all other mods.

 

 

 

Also, just FYI, in case it will go to this point (like it did for me), using AOP (aspect oriented programming) java based language will not work (MC environment does not allow easy integration of such, if it is not integrated by forge).

Or at least, it did not work for me as much as i tried to hook in Aspect J (you CAN hook it with a coremod, but at this point, there's no point).

[yooksi]

In some cases when method has no forge hooks, or other clear way of taking over calls, there is a an option that might* work if:

-Method is NOT static.

-Method is NOT private.

-Method is NOT final.

-Class is NOT final.

-You have / can gain access to classes' all instances.

 

When all of these (maybe not the * one, more about it in a second) are the case for you, you can create a class extending class that has the method and override it. Then what you have to do is replace all instances of class in question with your instance. It's easy if class is used as singleton, might be a bit harder if there are multiple instaces of it (but at that point, you always have a forge hook that allows accessing all/part of these instances).

Remember a few things though:

-Inner classes are not a problem, you'll just have to repeat process with its' external classes.

-If the instance(s) is/are stored in a private or final field, that's not a problem either. You have a way around both with reflection,

-If you have to default to vanilla(?) in overriden method, store instance that you replace and call it's method. It's very important, as other wise if other mods also use same replacement way...

 

*-If there are multiple mods using this way for the same thing, and one of them does not do it properly, it will break all other mods.

 

 

 

Also, just FYI, in case it will go to this point (like it did for me), using AOP (aspect oriented programming) java based language will not work (MC environment does not allow easy integration of such, if it is not integrated by forge).

Or at least, it did not work for me as much as i tried to hook in Aspect J (you CAN hook it with a coremod, but at this point, there's no point).

Replacing the instances is a difficult yet sometimes the only viable solution. Thanks for suggesting it.