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ABMs: Improve Introduction

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@ -9,22 +9,29 @@ redirect_from: /en/chapters/abms.html
## Introduction ## Introduction
An **A**ctive **B**lock **M**odifier (**ABM**) allows you to run code on An Active Block Modifier (ABM) is a method of periodically running a
certain nodes at specific intervals. function on nodes matching a criteria.
As the name implies, this only works on loaded MapBlocks.
Please be warned, ABMs which are too frequent or act on many nodes ABMs are best suited for nodes which are frequently found in the world,
cause massive amounts of lag. Use them sparingly. such as grass.
ABMs have a high CPU overhead, as Minetest needs to scan all Active Blocks
to find matching nodes, but they have a low memory and storage overhead.
* [Example: Growing Alien Grass](#example-growing-alien-grass) For nodes which are uncommon or already use metadata, such as furnaces
and machines, node timers should be used instead.
Node timers do not require scanning a MapBlock, but they do require slightly
more memory and storage to keep track of running timers.
* [Registering an ABM](#registering-an-abm)
* [Your Turn](#your-turn) * [Your Turn](#your-turn)
## Example: Growing Alien Grass ## Registering an ABM
Alien grass, for the purposes of this chapter, is a type of grass which Alien grass, for the purposes of this chapter, is a type of grass which
has a chance to appear near water. has a chance to appear near water.
To create it, you first need to register the grass, then
write an ABM.
```lua ```lua
minetest.register_node("aliens:grass", { minetest.register_node("aliens:grass", {
@ -48,21 +55,23 @@ minetest.register_abm({
}) })
``` ```
This ABM runs every ten seconds. There is a 1 in 5 chance of the ABM running on each This ABM runs every ten seconds.
node that has the correct name and the correct neighbours. If the ABM runs on a There is a 1 in 50 chance of the ABM running on each node that has the
node, an alien grass node is placed above it. Please be warned, this will delete any correct name and the correct neighbours.
node previously located in that position. To prevent this you should include a check If the ABM runs on a node, an alien grass node is placed above it.
using minetest.get_node to make sure there is space for the grass. Please be warned, this will delete any node previously located in that position.
To prevent this you should include a check using minetest.get_node to make sure there is space for the grass.
Specifying a neighbour is optional. If you specify multiple neighbours, only one of them Specifying a neighbour is optional.
needs to be present to meet the requirements. If you specify multiple neighbours, only one of them needs to be
present to meet the requirements.
Specifying chance is also optional. If you don't specify the chance, the ABM will Specifying chance is also optional.
always run when the other conditions are met. If you don't specify the chance, the ABM will always run when the other conditions are met.
## Your Turn ## Your Turn
* **Midas touch**: Make water turn to gold blocks with a 1 in 100 chance, every 5 seconds. * Midas touch: Make water turn to gold blocks with a 1 in 100 chance, every 5 seconds.
* **Decay**: Make wood turn into dirt when water is a neighbour. * Decay: Make wood turn into dirt when water is a neighbour.
* **Burnin'**: Make every air node catch on fire. (Tip: "air" and "fire:basic_flame"). * Burnin': Make every air node catch on fire. (Tip: "air" and "fire:basic_flame").
Warning: expect the game to crash. Warning: expect the game to crash.