Change Block gravity?

[deantonious]

Hi, I'm trying to change the gravity aceleration in minecraft. I have been looking for the class were I could change it, but I dindn't find anything... If it's not posible to change all the gravity in minecraft, maybe it's posible to change it in just one block?

 

Thanks

[Draco18s]

Gravity is not a globally referenced variable.  Every entity handles its own downward movement and acceleration.

(Blocks do not obey gravity, in any way, what so ever.  "But sand and gravel!" you say.  "Entities.  EntityFallingSand.  Not a block" I reply.)

[deantonious]

That's what I mean, how to change the acceleration of those entities.

[Draco18s]

ASM or Reflections.

 

Or base class editing.

[MineMaarten]

You could get the gravitational acceleration of every entity in the world by getting every entity in the world World#loadedEntityList. Then you get the entity type and create a fake entity of the same type you can then test on. Call Entity#onUpdate() on it and look at the motionY. That motion is it's gravitational acceleration (as no other forces apply except air drag, which is handled before the acceleration so that will have no effect). You now have the acceleration of that entity. If you want to make the entity have half the acceleration you can do Entity#motionY = -acceleration * 0.5D every tick.

 

I haven't tested this and this is quite resource intensive (as it will create a fake Entity object for every Entity every tick). This is a base concept though, and there are ways to make it more efficient (storing the accelerations of all the types of entities instead of recalculating them again and again).

[deantonious]

What I want is to simulate the real life gravity for the science class

Maybe If its easier, how could i do it editing the base classes?

[MineMaarten]

Well, then you could choose an Entity you want to perform the changes to, lets say the EntityItem. So I go to net.minecraft.entity.item.EntityItem.java.

 

On line 111 of the onUpdate() method you can see:

this.motionY -= 0.03999999910593033D;

Which is the gravity being applied to the entity, it appears to be 0.4 m/tick². If you look further in the method you see (from line 132) :

 float f = 0.98F;
(...)
this.motionX *= (double)f;
this.motionY *= 0.9800000190734863D;
this.motionZ *= (double)f;

Which is the air drag being applied. Every tick the entity loses 2% of its velocity. The code in the (...) handles the difference in slipperyness of blocks (and only applies to the X and Z motion).

 

So if you're not planning on releasing any mod, you can just change these parameters.

[deantonious]

Thank you, that's what I want