How can I find the height of the ground in Lua?

[Kodiologist]

The application here is that I'm writing a game that randomly chooses node positions the player is supposed to visit. The x- and z-coordinates are chosen without regard for terrain, but I'd like to choose the y-coordinate to be 1 unit above ground level at that point. So if the mapgen happens to make a mountain there, you'd have to climb it, or if the mapgen makes a lake there, you'd have to swim to the lakebed.

The Mapgen class seems to have a getGroundLevelAtPoint method at the C++ level, but it seems inaccessible to mods.

minetest.register_on_generated seems difficult to use for this purpose because the first generated slice of map including the (x, z) coordinates in question may not include the ground-level y-coordinate.

[Nore]

There was a pull request about that, but it was not merged: https://github.com/minetest/minetest/pull/640
The other possibility is to start somewhere in the ground (like y = -100), and while the light is less than 15 (sunlight), increase y. You then have ground level... (however, you need to wait that the area is generated before doing that...)

[aldobr]

start at 0 heigth.

if node is air, walk node by node, decreasing heigth by one until node no longer is air.
z positon is current position + 1
if node is not air, walk node by node, increasng heigth by one until node is air.
z position is current position

[Kodiologist]

There was a pull request about that, but it was not merged

Rats.

Lazy map generation seems to be the chief obstacle here. (x, -100, z) may well never be generated if the player doesn't dig down there. Similar concerns apply to your solution, aldobr. Is there any way to force generation of a map chunk containing a given node position?

[Nore]

You can always know if the player is above or below the level of ground (except lakebeds) by looking at the sunlight. So: if the player is somewhere where there is no sunlight, you know he is below ground level, etc.

[paramat]

Until the terrain generates at a particular distant x z location, the y value of ground level is undefined, the only way to know that in advance is to rewrite mapgen v6 in lua and do the perlin noise calculations to see where ground level will be, this is possible (i could do it but not interested) but not easy.

[Sokomine]

It wouldn't work if you redefine water to let sunlight through it.

In such a case, checking one node above might be enough. Perhaps the original poster doesn't care about positions on water anyway.

[Kodiologist]

Great, I seem to have been able to get this to work by checking the light level (as you suggested, Nore) along with a manual check for water. Here's my implementation in MoonScript:

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Code: Select all

MAX_LIGHT = 15
NOON = .5

waypoints = for _ = 1, 1
   {created: false,
    ymin: -1/0,  -- negative infinity
    ymax: 1/0,   -- positive infinity
    pos: {x: 5, z: 5}}
--waypoints = for _ = 1, 2
--   {created: false,
--    ymin: -1/0,    -- negative infinity
--    ymax: 1/0,   -- positive infinity
--    pos: {
--        x: (if coinflip! then 1 else -1) * math.random(100, 200),
--        z: (if coinflip! then 1 else -1) * math.random(100, 200)}}

minetest.register_on_generated (minp, maxp, blockseed) ->
    for wp in *waypoints
        if not wp.created and do
                wp.pos.x >= minp.x and wp.pos.x <= maxp.x and do
                wp.pos.z >= minp.z and wp.pos.z <= maxp.z
            for y = minp.y, maxp.y
                here = {x: wp.pos.x, y: y, z: wp.pos.z}
                if minetest.get_node_light(here, NOON) == MAX_LIGHT or do
                        minetest.get_node(here).name == 'default:water_source'
                    wp.ymax = math.min wp.ymax, y
                else
                    wp.ymin = math.max wp.ymin, y + 1
            if wp.ymin == wp.ymax
                wp.pos.y = wp.ymin
                wp.created = true