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| title | layout | root |
|---|---|---|
| Basic Map Operations | default | ../../ |
Introduction
In this chapter you will learn how to perform basic actions on the map.
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 %}
Moving and swapping nodes
Moving a node is the same as swapping a node, except that one of the nodes becomes air. Here is a naive example to move a node:
{% highlight lua %} -- DO NOT ACTUALLY USE THIS local pos1 = { x = 1, y = 3, z = 4 } local pos2 = vector.add(pos, { x = 1, y = 0, z = 0 }) local node1 = minetest.get_node(pos1) local node2 = minetest.get_node(pos2) minetest.set_node(pos1, node2) minetest.set_node(pos2, node1) -- DO NOT ACTUALLY USE THIS {% endhighlight %}
This won't copy any node meta data to the new position, or delete the old meta data. Luckily Minetest has a function which you can use instead of the above:
{% highlight lua %} minetest.swap_node(pos, vector.add(pos, { x = 1, y = 0, z = 0 })) {% 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 %}
Loading and Deleting
You can use minetest.emerge_area and minetest.delete_area to load
and delete map blocks.
To Do
This section will be added soon™.