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Last active Aug 29, 2015
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title: Active Block Modifiers
layout: default
root: ../
In this chapter we will learn how to create an **A**ctive **B**lock **M**odifier (**ABM**).
An active block modifier allows you to run code on certain nodes at certain
Please be warned, ABMs which are too frequent or act on too many nodes cause
massive amounts of lag. Use them lightly.
* Special Growing Grass
Special Growing Grass
We are now going to make a mod (Yay!).
It will add a type of grass called alien grass - it grows near water on grassy
{% highlight lua %}
minetest.register_node("aliens:grass", {
description = "Alien Grass",
light_source = 3, -- The node radiates light. Values can be from 1 to 15
tiles = {"aliens_grass.png"},
groups = {choppy=1},
on_use = minetest.item_eat(20)
nodenames = {"default:dirt_with_grass"},
neighbors = {"default:water_source", "default:water_flowing"},
interval = 10.0, -- Run every 10 seconds
chance = 50, -- Select every 1 in 50 nodes
action = function(pos, node, active_object_count, active_object_count_wider)
minetest.set_node({x = pos.x, y = pos.y + 1, z = pos.z}, {name = "aliens:grass"})
{% endhighlight %}
Every ten seconds the ABM is run. Each node which has the correct nodename and
the correct neighbors then has a 1 in 5 chance of being run. If a node is run on,
an alien grass block is placed above it. Please be warned, that will delete any
blocks above grass blocks - you should check there is space by doing minetest.get_node.
That's really all there is to ABMs. Specifying a neighbor is optional, so is chance.
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