Document VoxelArea

doc/VoxelArea.adoc

@@ -0,0 +1,99 @@
+= `VoxelArea`
+include::../include/config.adoc[]
+:description: Documentation for the `VoxelArea` "class"
+:keywords: voxel, area, voxelmanip
+
+The `VoxelArea` metatable provides an OOP-like utility for dealing with LuaVoxelManip (specifically, for doing the index math).
+
+== `VoxelArea.new(self, o)`
+
+Sets `self.__index` to `self` and `self` as the metatable of `o`, which can have the following fields:
+
+* `MinEdge`: Minimum position of the area, inclusive
+* `MaxEdge`: Maximum position of the area, inclusive
+
+Both positions should be `vector`s of integer numbers; each component of `MinEdge` should be smaller than the respective component of `MaxEdge` if the `VoxelArea` is to be non-empty. You can use `minp, maxp = vector.sort(minp, maxp)` to achieve this.
+
+Calculates `ystride` and `zstride` and stores both in `o`.
+
+Common usage:
+[source,lua]
+----
+local voxelmanip = minetest.get_voxel_manip(pos_min, pos_max)
+local emin, emax = voxelmanip:read_from_map(pos_min, pos_max)
+local voxelarea = VoxelArea:new{ MinEdge = emin, MaxEdge = emax }
+----
+
+WARNING: Always pass the actual emerged min & max positions. Do not pass the desired min & max positions.
+
+WARNING: Never pass fractional values as min- or max edge.
+
+TIP: You can use `vector.floor`, `vector.round` or `vector.apply(vec, math.ceil)` to guarantee integer values.
+
+The following methods can both be called in an imperative manner (`VoxelArea.<method>(self, ...)`) or an OOP manner (recommended): `self:<method>(...)`. The below examples are documented using the latter style, where `area` is a valid table with `VoxelArea` as the metatable.
+
+== `area:getExtent()`
+
+Returns the dimensions of `area` as integer `vector`.
+
+== `area:getVolume()`
+
+Returns the volume of `area` as integer.
+
+== `area:index(x, y, z)`
+
+`x`, `y`, `z` are absolute coordinates of a node within the area. Returns an integer index to be used for data tables returned by VoxelManip objects.
+
+WARNING: This will silently `floor` the returned index instead of throwing an error. Make sure that the coordinates you pass are (1) not fractional and (2) within the area.
+
+== `area:indexp(p)`
+
+Shorthand for `area:index(p.x, p.y, p.z)`.
+
+== `area:position(index)`
+
+Inverse to `area:indexp`. Returns the absolute node position corresponding to the `index` as a table with `x`, `y` and `z` fields.
+
+TIP: The returned table is missing the `vector` metatable. If it is not performance-critical, use `p = vector.new(area:position(index))` to create a copied vector with metatable.
+
+== `area:contains(x, y, z)`
+
+Returns `true` if all `x`, `y`, `z` coordinates are between the respective `MinEdge` and `MaxEdge` coordinates, both inclusive.
+
+== `area:containsp(p)`
+
+Shorthand for `area:contains(p.x, p.y, p.z)`
+
+== `area:containsi(i)`
+
+Returns `true` if `i` is between `1` and the `area` volume, both inclusive.
+
+WARNING: `area:containsi(area:indexp(p))` *is not equivalent to* `area:containsp(p)`, as `area:indexp` will happily produce valid indices for plenty out-of-area positions.
+
+== `area:iter(minx, miny, minz, maxx, maxy, maxz)`
+
+Returns an iterator (a function that returns the index of the current position and advances to the next one) that iterates in XYZ order (first incrementing X until the line has been finished, then Y until the plane has been finished, then Z until the cuboid has been finished).
+
+== `area:iterp(minp, maxp)`
+
+Shorthand for `area:iter(minp.x, minp.y, minp.z, maxp.x, maxp.y, maxp.z)`.
+
+Example:
+[source,lua]
+----
+for index in area:iterp(pos_min, pos_max) do
+	content_id_data[index] = ...
+end
+----
+which is equivalent to (but shorter & faster than):
+[source,lua]
+----
+for z = pos_min.z, pos_max.z do
+	for y = pos_min.y, pos_max.y do
+		for x = pos_min.x, pos_max.x do
+			local index = area:index(x, y, z)
+			content_id_data[index] = ...
+		end
+	end
+end
+----