minetest_modding_book/_en/map/environment.md

title	layout	root	idx	description
Basic Map Operations	default	../../	3.1	Basic operations like set_node and get_node

Introduction

In this chapter you will learn how to perform basic actions on the map.

• Map Structure
• Reading
  • Reading Nodes
  • Finding Nodes
• Writing
  • Writing Nodes
  • Removing Nodes
• Loading Blocks
• Deleting Blocks

Map Structure

The Minetest map is split into MapBlocks, each MapBlocks being a cube of size 16. As players travel around the map, MapBlocks are created, loaded, and unloaded. Areas of the map which are not yet loaded are full of ignore nodes, an impassable unselectable placeholder node. Empty space is full of air nodes, an invisible node you can walk through.

Loaded map blocks are often refered to as active blocks. Active Blocks can be read from or written to by mods or players, have active entities. The Engine also performs operations on the map, such as performing liquid physics.

MapBlocks can either be loaded from the world database or generated. MapBlocks will be generated up to the map generation limit (mapgen_limit) which is set at its maximum value, 31000, by default. Existing MapBlocks can however be loaded from the world database outside of the generation limit.

Reading

Reading Nodes

You can read from the map once you have a position:

{% highlight lua %} local node = minetest.get_node({ x = 1, y = 3, z = 4 }) print(dump(node)) --> { name=.., param1=.., param2=.. } {% endhighlight %}

If the position is a decimal, it will be rounded to the containing node. The function will always return a table containing the node information:

• name - The node name, will be ignore when the area is unloaded.
• param1 - See the node definition, will commonly be light.
• param2 - See the node definition.

It's worth noting that the function won't load the containing block if the block is inactive, but will instead return a table with name being ignore.

You can use minetest.get_node_or_nil instead, which will return nil rather than a table with a name of ignore. It still won't load the block, however. This may still return ignore if a block actually contains ignore. This will happen near the edge of the map as defined by the map generation limit (mapgen_limit).

Finding Nodes

Minetest offers a number of helper functions to speed up common map actions. The most commonly used of these are for finding nodes.

For example, say we wanted to make a certain type of plant that grows better near mese. You would need to search for any nearby mese nodes, and adapt the growth rate accordingly.

{% highlight lua %} local grow_speed = 1 local node_pos = minetest.find_node_near(pos, 5, { "default:mese" }) if node_pos then minetest.chat_send_all("Node found at: " .. dump(node_pos)) grow_speed = 2 end {% endhighlight %}

Lets say, for example, that the growth rate increases the more mese there is nearby. You should then use a function which can find multiple nodes in area:

{% highlight lua %} local pos1 = vector.subtract(pos, { x = 5, y = 5, z = 5 }) local pos2 = vector.add(pos, { x = 5, y = 5, z = 5 }) local pos_list = minetest.find_nodes_in_area(pos1, pos2, { "default:mese" }) local grow_speed = 1 + #pos_list {% endhighlight %}

The above code doesn't quite do what we want, as it checks based on area, whereas find_node_near checks based on range. In order to fix this we will, unfortunately, need to manually check the range ourselves.

{% highlight lua %} local pos1 = vector.subtract(pos, { x = 5, y = 5, z = 5 }) local pos2 = vector.add(pos, { x = 5, y = 5, z = 5 }) local pos_list = minetest.find_nodes_in_area(pos1, pos2, { "default:mese" }) local grow_speed = 1 for i=1, #pos_list do local delta = vector.subtract(pos_list[i], pos) if delta.xdelta.x + delta.ydelta.y <= 5*5 then grow_speed = grow_speed + 1 end end {% endhighlight %}

Now your code will correctly increase grow_speed based on mese nodes in range. Note how we compared the squared distance from the position, rather than square rooting it to obtain the actual distance. This is because computers find square roots computationally expensive, so you should avoid them as much as possible.

There are more variations of the above two functions, such as find_nodes_with_meta and find_nodes_in_area_under_air, which work in a similar way and are useful in other circumstances.

Writing

Writing Nodes

You can use set_node to write to the map. Each call to set_node will cause lighting to be recalculated, which means that set_node is fairly slow for large numbers of nodes.

{% highlight lua %} minetest.set_node({ x = 1, y = 3, z = 4 }, { name = "default:mese" })

local node = minetest.get_node({ x = 1, y = 3, z = 4 }) print(node.name) --> default:mese {% endhighlight %}

set_node will remove any associated meta data or inventory from that position. This isn't desirable in all circumstances, especially if you're using multiple node definitions to represent one conceptual node. An example of this is the furnace node - whilst you think conceptually of it as one node, it's actually two.

You can set a node without deleting meta data or the inventory like so:

{% highlight lua %} minetest.swap_node({ x = 1, y = 3, z = 4 }, { name = "default:mese" }) {% endhighlight %}

Removing Nodes

A node must always be present. When someone says to remove a node, what is usually meant is they want to set the node to air.

The following two lines will both remove a node, and are both identical:

{% highlight lua %} minetest.remove_node(pos) minetest.set_node(pos, { name = "air" }) {% endhighlight %}

In fact, remove_node will call set_node with name being air.

Loading Blocks

You can use minetest.emerge_area to load map blocks. Emerge area is asynchronous, meaning the the blocks won't be loaded instantly. Instead they will be loaded soon in the future, and the callback will be called each time.

{% highlight lua %} -- Load a 20x20x20 area local halfsize = { x = 10, y = 10, z = 10 } local pos1 = vector.subtract(pos, halfsize) local pos2 = vector.add (pos, halfsize)

local context = {} -- persist data between callback calls minetest.emerge_area(pos1, pos2, emerge_callback, context) {% endhighlight %}

Minetest will call emerge_callback whenever it loads a block, with some progress information.

{% highlight lua %} local function emerge_callback(pos, action, num_calls_remaining, context) -- On first call, record number of blocks if not context.total_blocks then context.total_blocks = num_calls_remaining + 1 context.loaded_blocks = 0 end

-- Increment number of blocks loaded
context.loaded_blocks = context.loaded_blocks + 1

-- Send progress message
if context.total_blocks == context.loaded_blocks then
    minetest.chat_send_all("Finished loading blocks!")
end
    local perc = 100 * context.loaded_blocks / context.total_blocks
    minetest.chat_send_all(string.format("Loading blocks %d/%d (%.2f%%)",
        context.loaded_blocks, context.total_blocks, perc)
end

end {% endhighlight %}

This is not the only way of loading blocks; Using a LVM will also cause the encompassed blocks to be loaded synchronously.

Deleting Blocks

You can use delete_blocks to delete a range of map blocks:

{% highlight lua %} -- Delete a 20x20x20 area local halfsize = { x = 10, y = 10, z = 10 } local pos1 = vector.subtract(pos, halfsize) local pos2 = vector.add (pos, halfsize)

minetest.delete_area(pos1, pos2) {% endhighlight %}

This will delete all map blocks in that area, inclusive. This means that some nodes will be deleted outside the area as they will be on a mapblock which overlaps the area bounds.